[RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.org>

Kbuild supports an architecture specific Makefile.postlink file that is
invoked for the vmlinux target after it has been built. This Makefile
takes 'vmlinux' (which has just been built) as the target, and mangles
the file and/or constructs other intermediate artifacts from it.

This violates the general philosophy of Make, which is based on rules
and dependencies, and artifacts that are rebuilt only when any of their
dependencies have been updated.

Instead, the different incarnations of vmlinux that are consumed by
different stages of the build should be emitted as distinct files, where
rules and dependencies are used to define one in terms of the other.

This also works around an error observed here [0], where vmlinux is
deleted by Make because a subsequent step that consumes it as input
throws an error.

So refactor the vmlinux shell scripts and build rules so that
architectures that rely on --emit-relocs to construct vmlinux with
static relocations preserved will get a separate vmlinux.unstripped file
carrying those relocations. This removes the need for an imperative
postlink step, given that any rules that depend on the unstripped
vmlinux can now simply depend on vmlinux.unstripped, rather than inject
a build step into Makefile.postlink

S390 should be able to do the same. MIPS and RISC-V perform some
post-build checks on vmlinux, which is reasonable in principle for a
postlink step, although deleting vmlinux when the check fails is equally
unhelpful.

[0] https://lore.kernel.org/all/Z5ARucnUgqjwBnrp@gmail.com/T/#m731ed0206949fc3f39fcc8a7b82fe348a8fc80c4

Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>

Ard Biesheuvel (4):
  Kbuild/link-vmlinux.sh: Make output file name configurable
  Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations
  Kbuild: Create intermediate vmlinux build with relocations preserved
  x86: Get rid of Makefile.postlink

 Makefile                          |  4 ++
 arch/Kconfig                      |  7 ++++
 arch/mips/Kconfig                 |  1 +
 arch/mips/Makefile                |  4 --
 arch/mips/Makefile.postlink       |  2 +-
 arch/riscv/Kconfig                |  1 +
 arch/riscv/Makefile               |  2 +-
 arch/riscv/Makefile.postlink      | 11 +-----
 arch/riscv/boot/Makefile          |  5 +--
 arch/s390/Kconfig                 |  1 +
 arch/s390/Makefile                |  2 +-
 arch/s390/Makefile.postlink       |  4 +-
 arch/x86/Kconfig                  |  1 +
 arch/x86/Makefile                 |  6 ---
 arch/x86/Makefile.postlink        | 40 --------------------
 arch/x86/boot/compressed/Makefile |  8 ++--
 scripts/Makefile.lib              |  2 +-
 scripts/Makefile.vmlinux          | 27 +++++++++----
 scripts/link-vmlinux.sh           | 11 +++---
 19 files changed, 52 insertions(+), 87 deletions(-)
 delete mode 100644 arch/x86/Makefile.postlink

-- 
2.48.1.601.g30ceb7b040-goog

[RFC PATCH 1/4] Kbuild/link-vmlinux.sh: Make output file name configurable

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.org>

In order to introduce an intermediate, non-stripped vmlinux build that
can be used by other build steps as an input, pass the output file name
to link-vmlinux.sh via its command line.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 scripts/Makefile.vmlinux |  2 +-
 scripts/link-vmlinux.sh  | 11 ++++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 873caaa55313..3523ce3ce3dc 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -69,7 +69,7 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
 
 # Final link of vmlinux with optional arch pass after final link
 cmd_link_vmlinux =							\
-	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)";		\
+	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
 targets += vmlinux
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 56a077d204cf..e55026128e05 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -31,6 +31,7 @@ set -e
 LD="$1"
 KBUILD_LDFLAGS="$2"
 LDFLAGS_vmlinux="$3"
+VMLINUX="$4"
 
 is_enabled() {
 	grep -q "^$1=y" include/config/auto.conf
@@ -278,7 +279,7 @@ fi
 
 strip_debug=
 
-vmlinux_link vmlinux
+vmlinux_link "${VMLINUX}"
 
 # fill in BTF IDs
 if is_enabled CONFIG_DEBUG_INFO_BTF; then
@@ -290,11 +291,11 @@ if is_enabled CONFIG_DEBUG_INFO_BTF; then
 	${RESOLVE_BTFIDS} ${RESOLVE_BTFIDS_ARGS} vmlinux
 fi
 
-mksysmap vmlinux System.map
+mksysmap "${VMLINUX}" System.map
 
 if is_enabled CONFIG_BUILDTIME_TABLE_SORT; then
-	info SORTTAB vmlinux
-	if ! sorttable vmlinux; then
+	info SORTTAB "${VMLINUX}"
+	if ! sorttable "${VMLINUX}"; then
 		echo >&2 Failed to sort kernel tables
 		exit 1
 	fi
@@ -310,4 +311,4 @@ if is_enabled CONFIG_KALLSYMS; then
 fi
 
 # For fixdep
-echo "vmlinux: $0" > .vmlinux.d
+echo "${VMLINUX}: $0" > ".${VMLINUX}.d"
-- 
2.48.1.601.g30ceb7b040-goog

[RFC PATCH 2/4] Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.org>

Some architectures build vmlinux with static relocations preserved, but
strip them again from the final vmlinux image. Arch specific tools
consume these static relocations in order to construct relocation tables
for KASLR.

The fact that vmlinux is created, consumed and subsequently updated goes
against the typical, declarative paradigm used by Make, which is based
on rules and dependencies. So as a first step towards cleaning this up,
introduce a Kconfig symbol to declare that the arch wants to consume the
static relocations emitted into vmlinux. This will be wired up further
in subsequent patches.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 Makefile            | 4 ++++
 arch/Kconfig        | 7 +++++++
 arch/mips/Kconfig   | 1 +
 arch/mips/Makefile  | 4 ----
 arch/riscv/Kconfig  | 1 +
 arch/riscv/Makefile | 2 +-
 arch/s390/Kconfig   | 1 +
 arch/s390/Makefile  | 2 +-
 arch/x86/Kconfig    | 1 +
 arch/x86/Makefile   | 6 ------
 10 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index 30dab4c8b012..a3302dce56de 100644
--- a/Makefile
+++ b/Makefile
@@ -1119,6 +1119,10 @@ ifdef CONFIG_LD_ORPHAN_WARN
 LDFLAGS_vmlinux += --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
 endif
 
+ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
+LDFLAGS_vmlinux	+= --emit-relocs --discard-none
+endif
+
 # Align the bit size of userspace programs with the kernel
 KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
 KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
diff --git a/arch/Kconfig b/arch/Kconfig
index b8a4ff365582..101a13fcde8e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1695,6 +1695,13 @@ config ARCH_HAS_KERNEL_FPU_SUPPORT
 	  Architectures that select this option can run floating-point code in
 	  the kernel, as described in Documentation/core-api/floating-point.rst.
 
+config ARCH_VMLINUX_NEEDS_RELOCS
+	bool
+	help
+	  Whether the architecture needs vmlinux to be built with static
+	  relocations preserved. This is used by some architectures to
+	  construct bespoke relocation tables for KASLR.
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 1924f2d83932..5aedbd7afadb 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2617,6 +2617,7 @@ config RELOCATABLE
 		   CPU_MIPS32_R6 || CPU_MIPS64_R6 || \
 		   CPU_P5600 || CAVIUM_OCTEON_SOC || \
 		   CPU_LOONGSON64
+	select ARCH_VMLINUX_NEEDS_RELOCS
 	help
 	  This builds a kernel image that retains relocation information
 	  so it can be loaded someplace besides the default 1MB.
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index be8cb44a89fd..d9057e29bc62 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -100,10 +100,6 @@ LDFLAGS_vmlinux			+= -G 0 -static -n -nostdlib
 KBUILD_AFLAGS_MODULE		+= -mlong-calls
 KBUILD_CFLAGS_MODULE		+= -mlong-calls
 
-ifeq ($(CONFIG_RELOCATABLE),y)
-LDFLAGS_vmlinux			+= --emit-relocs
-endif
-
 cflags-y += -ffreestanding
 
 cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= -EB
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7612c52e9b1e..6f5800114416 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -1077,6 +1077,7 @@ config RELOCATABLE
 	bool "Build a relocatable kernel"
 	depends on MMU && 64BIT && !XIP_KERNEL
 	select MODULE_SECTIONS if MODULES
+	select ARCH_VMLINUX_NEEDS_RELOCS
 	help
           This builds a kernel as a Position Independent Executable (PIE),
           which retains all relocation metadata required to relocate the
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 13fbc0f94238..6ef0d10e0c50 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -8,7 +8,7 @@
 
 LDFLAGS_vmlinux := -z norelro
 ifeq ($(CONFIG_RELOCATABLE),y)
-	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext --emit-relocs
+	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext
 	KBUILD_CFLAGS += -fPIE
 endif
 ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9c9ec08d78c7..ea67b7317138 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -630,6 +630,7 @@ endchoice
 
 config RELOCATABLE
 	def_bool y
+	select ARCH_VMLINUX_NEEDS_RELOCS
 	help
 	  This builds a kernel image that retains relocation information
 	  so it can be loaded at an arbitrary address.
diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index 5fae311203c2..d5f4be440879 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -15,7 +15,7 @@ KBUILD_CFLAGS_MODULE += -fPIC
 KBUILD_AFLAGS	+= -m64
 KBUILD_CFLAGS	+= -m64
 KBUILD_CFLAGS	+= -fPIC
-LDFLAGS_vmlinux	:= -no-pie --emit-relocs --discard-none
+LDFLAGS_vmlinux	:= -no-pie
 extra_tools	:= relocs
 aflags_dwarf	:= -Wa,-gdwarf-2
 KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index be2c311f5118..2005d80ff8d1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2199,6 +2199,7 @@ config RANDOMIZE_BASE
 config X86_NEED_RELOCS
 	def_bool y
 	depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE)
+	select ARCH_VMLINUX_NEEDS_RELOCS
 
 config PHYSICAL_ALIGN
 	hex "Alignment value to which kernel should be aligned"
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b773b34768d..f65ed6dcd6fb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -251,12 +251,6 @@ endif
 
 KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
 
-ifdef CONFIG_X86_NEED_RELOCS
-LDFLAGS_vmlinux := --emit-relocs --discard-none
-else
-LDFLAGS_vmlinux :=
-endif
-
 #
 # The 64-bit kernel must be aligned to 2MB.  Pass -z max-page-size=0x200000 to
 # the linker to force 2MB page size regardless of the default page size used
-- 
2.48.1.601.g30ceb7b040-goog

Re: [RFC PATCH 2/4] Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations

[Masahiro Yamada]

On Mon, Feb 24, 2025 at 10:21 PM Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> Some architectures build vmlinux with static relocations preserved, but
> strip them again from the final vmlinux image. Arch specific tools
> consume these static relocations in order to construct relocation tables
> for KASLR.
>
> The fact that vmlinux is created, consumed and subsequently updated goes
> against the typical, declarative paradigm used by Make, which is based
> on rules and dependencies. So as a first step towards cleaning this up,
> introduce a Kconfig symbol to declare that the arch wants to consume the
> static relocations emitted into vmlinux. This will be wired up further
> in subsequent patches.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

I have no objection to this patch.

The code diff seems a good clean-up.


> ---
>  Makefile            | 4 ++++
>  arch/Kconfig        | 7 +++++++
>  arch/mips/Kconfig   | 1 +
>  arch/mips/Makefile  | 4 ----
>  arch/riscv/Kconfig  | 1 +
>  arch/riscv/Makefile | 2 +-
>  arch/s390/Kconfig   | 1 +
>  arch/s390/Makefile  | 2 +-
>  arch/x86/Kconfig    | 1 +
>  arch/x86/Makefile   | 6 ------
>  10 files changed, 17 insertions(+), 12 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 30dab4c8b012..a3302dce56de 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1119,6 +1119,10 @@ ifdef CONFIG_LD_ORPHAN_WARN
>  LDFLAGS_vmlinux += --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
>  endif
>
> +ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
> +LDFLAGS_vmlinux        += --emit-relocs --discard-none
> +endif
> +
>  # Align the bit size of userspace programs with the kernel
>  KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
>  KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
> diff --git a/arch/Kconfig b/arch/Kconfig
> index b8a4ff365582..101a13fcde8e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1695,6 +1695,13 @@ config ARCH_HAS_KERNEL_FPU_SUPPORT
>           Architectures that select this option can run floating-point code in
>           the kernel, as described in Documentation/core-api/floating-point.rst.
>
> +config ARCH_VMLINUX_NEEDS_RELOCS
> +       bool
> +       help
> +         Whether the architecture needs vmlinux to be built with static
> +         relocations preserved. This is used by some architectures to
> +         construct bespoke relocation tables for KASLR.
> +
>  source "kernel/gcov/Kconfig"
>
>  source "scripts/gcc-plugins/Kconfig"
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 1924f2d83932..5aedbd7afadb 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -2617,6 +2617,7 @@ config RELOCATABLE
>                    CPU_MIPS32_R6 || CPU_MIPS64_R6 || \
>                    CPU_P5600 || CAVIUM_OCTEON_SOC || \
>                    CPU_LOONGSON64
> +       select ARCH_VMLINUX_NEEDS_RELOCS
>         help
>           This builds a kernel image that retains relocation information
>           so it can be loaded someplace besides the default 1MB.
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index be8cb44a89fd..d9057e29bc62 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -100,10 +100,6 @@ LDFLAGS_vmlinux                    += -G 0 -static -n -nostdlib
>  KBUILD_AFLAGS_MODULE           += -mlong-calls
>  KBUILD_CFLAGS_MODULE           += -mlong-calls
>
> -ifeq ($(CONFIG_RELOCATABLE),y)
> -LDFLAGS_vmlinux                        += --emit-relocs
> -endif
> -
>  cflags-y += -ffreestanding
>
>  cflags-$(CONFIG_CPU_BIG_ENDIAN)                += -EB
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 7612c52e9b1e..6f5800114416 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -1077,6 +1077,7 @@ config RELOCATABLE
>         bool "Build a relocatable kernel"
>         depends on MMU && 64BIT && !XIP_KERNEL
>         select MODULE_SECTIONS if MODULES
> +       select ARCH_VMLINUX_NEEDS_RELOCS
>         help
>            This builds a kernel as a Position Independent Executable (PIE),
>            which retains all relocation metadata required to relocate the
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 13fbc0f94238..6ef0d10e0c50 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -8,7 +8,7 @@
>
>  LDFLAGS_vmlinux := -z norelro
>  ifeq ($(CONFIG_RELOCATABLE),y)
> -       LDFLAGS_vmlinux += -shared -Bsymbolic -z notext --emit-relocs
> +       LDFLAGS_vmlinux += -shared -Bsymbolic -z notext
>         KBUILD_CFLAGS += -fPIE
>  endif
>  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 9c9ec08d78c7..ea67b7317138 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -630,6 +630,7 @@ endchoice
>
>  config RELOCATABLE
>         def_bool y
> +       select ARCH_VMLINUX_NEEDS_RELOCS
>         help
>           This builds a kernel image that retains relocation information
>           so it can be loaded at an arbitrary address.
> diff --git a/arch/s390/Makefile b/arch/s390/Makefile
> index 5fae311203c2..d5f4be440879 100644
> --- a/arch/s390/Makefile
> +++ b/arch/s390/Makefile
> @@ -15,7 +15,7 @@ KBUILD_CFLAGS_MODULE += -fPIC
>  KBUILD_AFLAGS  += -m64
>  KBUILD_CFLAGS  += -m64
>  KBUILD_CFLAGS  += -fPIC
> -LDFLAGS_vmlinux        := -no-pie --emit-relocs --discard-none
> +LDFLAGS_vmlinux        := -no-pie
>  extra_tools    := relocs
>  aflags_dwarf   := -Wa,-gdwarf-2
>  KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index be2c311f5118..2005d80ff8d1 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2199,6 +2199,7 @@ config RANDOMIZE_BASE
>  config X86_NEED_RELOCS
>         def_bool y
>         depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE)
> +       select ARCH_VMLINUX_NEEDS_RELOCS
>
>  config PHYSICAL_ALIGN
>         hex "Alignment value to which kernel should be aligned"
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 5b773b34768d..f65ed6dcd6fb 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -251,12 +251,6 @@ endif
>
>  KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
>
> -ifdef CONFIG_X86_NEED_RELOCS
> -LDFLAGS_vmlinux := --emit-relocs --discard-none
> -else
> -LDFLAGS_vmlinux :=
> -endif
> -
>  #
>  # The 64-bit kernel must be aligned to 2MB.  Pass -z max-page-size=0x200000 to
>  # the linker to force 2MB page size regardless of the default page size used
> --
> 2.48.1.601.g30ceb7b040-goog
>
>


-- 
Best Regards
Masahiro Yamada

[RFC PATCH 3/4] Kbuild: Create intermediate vmlinux build with relocations preserved

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.org>

The imperative paradigm used to build vmlinux, extract some info from it
or perform some checks on it, and subsequently modify it again goes
against the declarative paradigm that is usually employed for defining
make rules.

In particular, the Makefile.postlink files that consume their input via
an output rule result in some dodgy logic in the decompressor makefiles
for RISC-V and x86, given that the vmlinux.relocs input file needed to
generate the arch-specific relocation tables may not exist or be out of
date, but cannot be constructed using the ordinary Make dependency based
rules, because the info needs to be extracted while vmlinux is in its
ephemeral, non-stripped form.

So instead, for architectures that require the static relocations that
are emitted into vmlinux when passing --emit-relocs to the linker, and
are subsequently stripped out again, introduce an intermediate vmlinux
target called vmlinux.unstripped, and organize the reset of the build
logic accordingly:

- vmlinux.unstripped is created only once, and not updated again
- build rules under arch/*/boot can depend on vmlinux.unstripped without
  running the risk of the data disappearing or being out of date
- the final vmlinux generated by the build is not bloated with static
  relocations that are never needed again after the build completes.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/mips/Makefile.postlink  |  2 +-
 arch/riscv/Makefile.postlink | 11 +--------
 arch/riscv/boot/Makefile     |  5 +---
 arch/s390/Makefile.postlink  |  4 +---
 arch/x86/Makefile.postlink   |  8 +++----
 scripts/Makefile.lib         |  2 +-
 scripts/Makefile.vmlinux     | 25 ++++++++++++++------
 7 files changed, 26 insertions(+), 31 deletions(-)

diff --git a/arch/mips/Makefile.postlink b/arch/mips/Makefile.postlink
index 6cfdc149d3bc..ea0add7d56b2 100644
--- a/arch/mips/Makefile.postlink
+++ b/arch/mips/Makefile.postlink
@@ -22,7 +22,7 @@ quiet_cmd_relocs = RELOCS  $@
 
 # `@true` prevents complaint when there is nothing to be done
 
-vmlinux: FORCE
+vmlinux vmlinux.unstripped: FORCE
 	@true
 ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y)
 	$(call if_changed,ls3_llsc)
diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
index 6b0580949b6a..0e4cf8ad2f14 100644
--- a/arch/riscv/Makefile.postlink
+++ b/arch/riscv/Makefile.postlink
@@ -10,26 +10,17 @@ __archpost:
 
 -include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
-include $(srctree)/scripts/Makefile.lib
 
 quiet_cmd_relocs_check = CHKREL  $@
 cmd_relocs_check = 							\
 	$(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
 
-ifdef CONFIG_RELOCATABLE
-quiet_cmd_cp_vmlinux_relocs = CPREL   vmlinux.relocs
-cmd_cp_vmlinux_relocs = cp vmlinux vmlinux.relocs
-
-endif
-
 # `@true` prevents complaint when there is nothing to be done
 
-vmlinux: FORCE
+vmlinux vmlinux.unstripped: FORCE
 	@true
 ifdef CONFIG_RELOCATABLE
 	$(call if_changed,relocs_check)
-	$(call if_changed,cp_vmlinux_relocs)
-	$(call if_changed,strip_relocs)
 endif
 
 clean:
diff --git a/arch/riscv/boot/Makefile b/arch/riscv/boot/Makefile
index b25d524ce5eb..bfc3d0b75b9b 100644
--- a/arch/riscv/boot/Makefile
+++ b/arch/riscv/boot/Makefile
@@ -32,10 +32,7 @@ $(obj)/xipImage: vmlinux FORCE
 endif
 
 ifdef CONFIG_RELOCATABLE
-vmlinux.relocs: vmlinux
-	@ (! [ -f vmlinux.relocs ] && echo "vmlinux.relocs can't be found, please remove vmlinux and try again") || true
-
-$(obj)/Image: vmlinux.relocs FORCE
+$(obj)/Image: vmlinux.unstripped FORCE
 else
 $(obj)/Image: vmlinux FORCE
 endif
diff --git a/arch/s390/Makefile.postlink b/arch/s390/Makefile.postlink
index 1ae5478cd6ac..c2b737500a91 100644
--- a/arch/s390/Makefile.postlink
+++ b/arch/s390/Makefile.postlink
@@ -11,7 +11,6 @@ __archpost:
 
 -include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
-include $(srctree)/scripts/Makefile.lib
 
 CMD_RELOCS=arch/s390/tools/relocs
 OUT_RELOCS = arch/s390/boot
@@ -20,9 +19,8 @@ quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/relocs.S
 	mkdir -p $(OUT_RELOCS); \
 	$(CMD_RELOCS) $@ > $(OUT_RELOCS)/relocs.S
 
-vmlinux: FORCE
+vmlinux.unstripped: FORCE
 	$(call cmd,relocs)
-	$(call cmd,strip_relocs)
 
 clean:
 	@rm -f $(OUT_RELOCS)/relocs.S
diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink
index 8b8a68162c94..445fce66630f 100644
--- a/arch/x86/Makefile.postlink
+++ b/arch/x86/Makefile.postlink
@@ -11,23 +11,21 @@ __archpost:
 
 -include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
-include $(srctree)/scripts/Makefile.lib
 
 CMD_RELOCS = arch/x86/tools/relocs
 OUT_RELOCS = arch/x86/boot/compressed
-quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/$@.relocs
+quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/vmlinux.relocs
       cmd_relocs = \
 	mkdir -p $(OUT_RELOCS); \
-	$(CMD_RELOCS) $@ > $(OUT_RELOCS)/$@.relocs; \
+	$(CMD_RELOCS) $@ > $(OUT_RELOCS)/vmlinux.relocs; \
 	$(CMD_RELOCS) --abs-relocs $@
 
 # `@true` prevents complaint when there is nothing to be done
 
-vmlinux: FORCE
+vmlinux vmlinux.unstripped: FORCE
 	@true
 ifeq ($(CONFIG_X86_NEED_RELOCS),y)
 	$(call cmd,relocs)
-	$(call cmd,strip_relocs)
 endif
 
 clean:
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index cad20f0e66ee..7a023f17a21d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -377,7 +377,7 @@ quiet_cmd_objcopy = OBJCOPY $@
 cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
 
 quiet_cmd_strip_relocs = RSTRIP  $@
-cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $@
+cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $< $@
 
 # Gzip
 # ---------------------------------------------------------------------------
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 3523ce3ce3dc..1e3ea8e4b4b0 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -9,6 +9,17 @@ include $(srctree)/scripts/Makefile.lib
 
 targets :=
 
+ifdef CONFIG_ARCH_VMLINUX_NEEDS_RELOCS
+vmlinux-final := vmlinux.unstripped
+
+vmlinux: $(vmlinux-final) FORCE
+	$(call if_changed,strip_relocs)
+
+targets += vmlinux
+else
+vmlinux-final := vmlinux
+endif
+
 %.o: %.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
@@ -47,7 +58,7 @@ targets += .builtin-dtbs-list
 
 ifdef CONFIG_GENERIC_BUILTIN_DTB
 targets += .builtin-dtbs.S .builtin-dtbs.o
-vmlinux: .builtin-dtbs.o
+$(vmlinux-final): .builtin-dtbs.o
 endif
 
 # vmlinux
@@ -55,11 +66,11 @@ endif
 
 ifdef CONFIG_MODULES
 targets += .vmlinux.export.o
-vmlinux: .vmlinux.export.o
+$(vmlinux-final): .vmlinux.export.o
 endif
 
 ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
-vmlinux: arch/$(SRCARCH)/tools/vmlinux.arch.o
+$(vmlinux-final): arch/$(SRCARCH)/tools/vmlinux.arch.o
 
 arch/$(SRCARCH)/tools/vmlinux.arch.o: vmlinux.o FORCE
 	$(Q)$(MAKE) $(build)=arch/$(SRCARCH)/tools $@
@@ -72,11 +83,11 @@ cmd_link_vmlinux =							\
 	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
-targets += vmlinux
-vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
+targets += $(vmlinux-final)
+$(vmlinux-final): scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
 	+$(call if_changed_dep,link_vmlinux)
 ifdef CONFIG_DEBUG_INFO_BTF
-vmlinux: $(RESOLVE_BTFIDS)
+$(vmlinux-final): $(RESOLVE_BTFIDS)
 endif
 
 # module.builtin.ranges
@@ -92,7 +103,7 @@ modules.builtin.ranges: $(srctree)/scripts/generate_builtin_ranges.awk \
 			modules.builtin vmlinux.map vmlinux.o.map FORCE
 	$(call if_changed,modules_builtin_ranges)
 
-vmlinux.map: vmlinux
+vmlinux.map: $(vmlinux-final)
 	@:
 
 endif
-- 
2.48.1.601.g30ceb7b040-goog

Re: [RFC PATCH 3/4] Kbuild: Create intermediate vmlinux build with relocations preserved

[Masahiro Yamada]

On Mon, Feb 24, 2025 at 10:22 PM Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> The imperative paradigm used to build vmlinux, extract some info from it
> or perform some checks on it, and subsequently modify it again goes
> against the declarative paradigm that is usually employed for defining
> make rules.
>
> In particular, the Makefile.postlink files that consume their input via
> an output rule result in some dodgy logic in the decompressor makefiles
> for RISC-V and x86, given that the vmlinux.relocs input file needed to
> generate the arch-specific relocation tables may not exist or be out of
> date, but cannot be constructed using the ordinary Make dependency based
> rules, because the info needs to be extracted while vmlinux is in its
> ephemeral, non-stripped form.
>
> So instead, for architectures that require the static relocations that
> are emitted into vmlinux when passing --emit-relocs to the linker, and
> are subsequently stripped out again, introduce an intermediate vmlinux
> target called vmlinux.unstripped, and organize the reset of the build
> logic accordingly:
>
> - vmlinux.unstripped is created only once, and not updated again
> - build rules under arch/*/boot can depend on vmlinux.unstripped without
>   running the risk of the data disappearing or being out of date
> - the final vmlinux generated by the build is not bloated with static
>   relocations that are never needed again after the build completes.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---

I already expressed my concern in the cover-letter.

Other than that, there are some nits:

 - You need to update .gitignore to ignore vmlinux.unstripped
  and the 'clean' target to clean up vmlinux.unstripped.

- cmd_strip_relocs can be moved to scripts/Makefile.vmlinux
  from scripts/Makefile.lib




>  arch/mips/Makefile.postlink  |  2 +-
>  arch/riscv/Makefile.postlink | 11 +--------
>  arch/riscv/boot/Makefile     |  5 +---
>  arch/s390/Makefile.postlink  |  4 +---
>  arch/x86/Makefile.postlink   |  8 +++----
>  scripts/Makefile.lib         |  2 +-
>  scripts/Makefile.vmlinux     | 25 ++++++++++++++------
>  7 files changed, 26 insertions(+), 31 deletions(-)
>
> diff --git a/arch/mips/Makefile.postlink b/arch/mips/Makefile.postlink
> index 6cfdc149d3bc..ea0add7d56b2 100644
> --- a/arch/mips/Makefile.postlink
> +++ b/arch/mips/Makefile.postlink
> @@ -22,7 +22,7 @@ quiet_cmd_relocs = RELOCS  $@
>
>  # `@true` prevents complaint when there is nothing to be done
>
> -vmlinux: FORCE
> +vmlinux vmlinux.unstripped: FORCE
>         @true
>  ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y)
>         $(call if_changed,ls3_llsc)
> diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
> index 6b0580949b6a..0e4cf8ad2f14 100644
> --- a/arch/riscv/Makefile.postlink
> +++ b/arch/riscv/Makefile.postlink
> @@ -10,26 +10,17 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> -include $(srctree)/scripts/Makefile.lib
>
>  quiet_cmd_relocs_check = CHKREL  $@
>  cmd_relocs_check =                                                     \
>         $(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
>
> -ifdef CONFIG_RELOCATABLE
> -quiet_cmd_cp_vmlinux_relocs = CPREL   vmlinux.relocs
> -cmd_cp_vmlinux_relocs = cp vmlinux vmlinux.relocs
> -
> -endif
> -
>  # `@true` prevents complaint when there is nothing to be done
>
> -vmlinux: FORCE
> +vmlinux vmlinux.unstripped: FORCE
>         @true
>  ifdef CONFIG_RELOCATABLE
>         $(call if_changed,relocs_check)
> -       $(call if_changed,cp_vmlinux_relocs)
> -       $(call if_changed,strip_relocs)
>  endif
>
>  clean:
> diff --git a/arch/riscv/boot/Makefile b/arch/riscv/boot/Makefile
> index b25d524ce5eb..bfc3d0b75b9b 100644
> --- a/arch/riscv/boot/Makefile
> +++ b/arch/riscv/boot/Makefile
> @@ -32,10 +32,7 @@ $(obj)/xipImage: vmlinux FORCE
>  endif
>
>  ifdef CONFIG_RELOCATABLE
> -vmlinux.relocs: vmlinux
> -       @ (! [ -f vmlinux.relocs ] && echo "vmlinux.relocs can't be found, please remove vmlinux and try again") || true
> -
> -$(obj)/Image: vmlinux.relocs FORCE
> +$(obj)/Image: vmlinux.unstripped FORCE
>  else
>  $(obj)/Image: vmlinux FORCE
>  endif
> diff --git a/arch/s390/Makefile.postlink b/arch/s390/Makefile.postlink
> index 1ae5478cd6ac..c2b737500a91 100644
> --- a/arch/s390/Makefile.postlink
> +++ b/arch/s390/Makefile.postlink
> @@ -11,7 +11,6 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> -include $(srctree)/scripts/Makefile.lib
>
>  CMD_RELOCS=arch/s390/tools/relocs
>  OUT_RELOCS = arch/s390/boot
> @@ -20,9 +19,8 @@ quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/relocs.S
>         mkdir -p $(OUT_RELOCS); \
>         $(CMD_RELOCS) $@ > $(OUT_RELOCS)/relocs.S
>
> -vmlinux: FORCE
> +vmlinux.unstripped: FORCE
>         $(call cmd,relocs)
> -       $(call cmd,strip_relocs)
>
>  clean:
>         @rm -f $(OUT_RELOCS)/relocs.S
> diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink
> index 8b8a68162c94..445fce66630f 100644
> --- a/arch/x86/Makefile.postlink
> +++ b/arch/x86/Makefile.postlink
> @@ -11,23 +11,21 @@ __archpost:
>
>  -include include/config/auto.conf
>  include $(srctree)/scripts/Kbuild.include
> -include $(srctree)/scripts/Makefile.lib
>
>  CMD_RELOCS = arch/x86/tools/relocs
>  OUT_RELOCS = arch/x86/boot/compressed
> -quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/$@.relocs
> +quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/vmlinux.relocs
>        cmd_relocs = \
>         mkdir -p $(OUT_RELOCS); \
> -       $(CMD_RELOCS) $@ > $(OUT_RELOCS)/$@.relocs; \
> +       $(CMD_RELOCS) $@ > $(OUT_RELOCS)/vmlinux.relocs; \
>         $(CMD_RELOCS) --abs-relocs $@
>
>  # `@true` prevents complaint when there is nothing to be done
>
> -vmlinux: FORCE
> +vmlinux vmlinux.unstripped: FORCE
>         @true
>  ifeq ($(CONFIG_X86_NEED_RELOCS),y)
>         $(call cmd,relocs)
> -       $(call cmd,strip_relocs)
>  endif
>
>  clean:
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index cad20f0e66ee..7a023f17a21d 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -377,7 +377,7 @@ quiet_cmd_objcopy = OBJCOPY $@
>  cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
>
>  quiet_cmd_strip_relocs = RSTRIP  $@
> -cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $@
> +cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $< $@
>
>  # Gzip
>  # ---------------------------------------------------------------------------
> diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
> index 3523ce3ce3dc..1e3ea8e4b4b0 100644
> --- a/scripts/Makefile.vmlinux
> +++ b/scripts/Makefile.vmlinux
> @@ -9,6 +9,17 @@ include $(srctree)/scripts/Makefile.lib
>
>  targets :=
>
> +ifdef CONFIG_ARCH_VMLINUX_NEEDS_RELOCS
> +vmlinux-final := vmlinux.unstripped
> +
> +vmlinux: $(vmlinux-final) FORCE
> +       $(call if_changed,strip_relocs)
> +
> +targets += vmlinux
> +else
> +vmlinux-final := vmlinux
> +endif
> +
>  %.o: %.c FORCE
>         $(call if_changed_rule,cc_o_c)
>
> @@ -47,7 +58,7 @@ targets += .builtin-dtbs-list
>
>  ifdef CONFIG_GENERIC_BUILTIN_DTB
>  targets += .builtin-dtbs.S .builtin-dtbs.o
> -vmlinux: .builtin-dtbs.o
> +$(vmlinux-final): .builtin-dtbs.o
>  endif
>
>  # vmlinux
> @@ -55,11 +66,11 @@ endif
>
>  ifdef CONFIG_MODULES
>  targets += .vmlinux.export.o
> -vmlinux: .vmlinux.export.o
> +$(vmlinux-final): .vmlinux.export.o
>  endif
>
>  ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
> -vmlinux: arch/$(SRCARCH)/tools/vmlinux.arch.o
> +$(vmlinux-final): arch/$(SRCARCH)/tools/vmlinux.arch.o
>
>  arch/$(SRCARCH)/tools/vmlinux.arch.o: vmlinux.o FORCE
>         $(Q)$(MAKE) $(build)=arch/$(SRCARCH)/tools $@
> @@ -72,11 +83,11 @@ cmd_link_vmlinux =                                                  \
>         $< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";       \
>         $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
>
> -targets += vmlinux
> -vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
> +targets += $(vmlinux-final)
> +$(vmlinux-final): scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
>         +$(call if_changed_dep,link_vmlinux)
>  ifdef CONFIG_DEBUG_INFO_BTF
> -vmlinux: $(RESOLVE_BTFIDS)
> +$(vmlinux-final): $(RESOLVE_BTFIDS)
>  endif
>
>  # module.builtin.ranges
> @@ -92,7 +103,7 @@ modules.builtin.ranges: $(srctree)/scripts/generate_builtin_ranges.awk \
>                         modules.builtin vmlinux.map vmlinux.o.map FORCE
>         $(call if_changed,modules_builtin_ranges)
>
> -vmlinux.map: vmlinux
> +vmlinux.map: $(vmlinux-final)
>         @:
>
>  endif
> --
> 2.48.1.601.g30ceb7b040-goog
>
>


-- 
Best Regards
Masahiro Yamada

[RFC PATCH 4/4] x86: Get rid of Makefile.postlink

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb@kernel.org>

Instead of generating the vmlinux.relocs file (needed by the
decompressor build to construct the KASLR relocation tables) as a
vmlinux postlink step, which is dubious because it depends on data that
is stripped from vmlinux before the build completes, generate it from
vmlinux.unstripped, which has been introduced specifically for this
purpose.

This ensures that each artifact is rebuilt as needed, rather than as a
side effect of another build rule.

This effectively reverts commit

  9d9173e9ceb6 ("x86/build: Avoid relocation information in final vmlinux")

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/Makefile.postlink        | 38 --------------------
 arch/x86/boot/compressed/Makefile |  8 +++--
 2 files changed, 5 insertions(+), 41 deletions(-)

diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink
deleted file mode 100644
index 445fce66630f..000000000000
--- a/arch/x86/Makefile.postlink
+++ /dev/null
@@ -1,38 +0,0 @@
-# SPDX-License-Identifier: GPL-2.0
-# ===========================================================================
-# Post-link x86 pass
-# ===========================================================================
-#
-# 1. Separate relocations from vmlinux into vmlinux.relocs.
-# 2. Strip relocations from vmlinux.
-
-PHONY := __archpost
-__archpost:
-
--include include/config/auto.conf
-include $(srctree)/scripts/Kbuild.include
-
-CMD_RELOCS = arch/x86/tools/relocs
-OUT_RELOCS = arch/x86/boot/compressed
-quiet_cmd_relocs = RELOCS  $(OUT_RELOCS)/vmlinux.relocs
-      cmd_relocs = \
-	mkdir -p $(OUT_RELOCS); \
-	$(CMD_RELOCS) $@ > $(OUT_RELOCS)/vmlinux.relocs; \
-	$(CMD_RELOCS) --abs-relocs $@
-
-# `@true` prevents complaint when there is nothing to be done
-
-vmlinux vmlinux.unstripped: FORCE
-	@true
-ifeq ($(CONFIG_X86_NEED_RELOCS),y)
-	$(call cmd,relocs)
-endif
-
-clean:
-	@rm -f $(OUT_RELOCS)/vmlinux.relocs
-
-PHONY += FORCE clean
-
-FORCE:
-
-.PHONY: $(PHONY)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 606c74f27459..8b7da3fc3f03 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -117,9 +117,11 @@ $(obj)/vmlinux.bin: vmlinux FORCE
 
 targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs
 
-# vmlinux.relocs is created by the vmlinux postlink step.
-$(obj)/vmlinux.relocs: vmlinux
-	@true
+CMD_RELOCS = arch/x86/tools/relocs
+quiet_cmd_relocs = RELOCS  $@
+      cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
+$(obj)/vmlinux.relocs: vmlinux.unstripped FORCE
+	$(call if_changed,relocs)
 
 vmlinux.bin.all-y := $(obj)/vmlinux.bin
 vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs
-- 
2.48.1.601.g30ceb7b040-goog

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ingo Molnar]

* Ard Biesheuvel <ardb+git@google.com> wrote:

> From: Ard Biesheuvel <ardb@kernel.org>
> 
> Kbuild supports an architecture specific Makefile.postlink file that is
> invoked for the vmlinux target after it has been built. This Makefile
> takes 'vmlinux' (which has just been built) as the target, and mangles
> the file and/or constructs other intermediate artifacts from it.
> 
> This violates the general philosophy of Make, which is based on rules
> and dependencies, and artifacts that are rebuilt only when any of their
> dependencies have been updated.
> 
> Instead, the different incarnations of vmlinux that are consumed by
> different stages of the build should be emitted as distinct files, where
> rules and dependencies are used to define one in terms of the other.
> 
> This also works around an error observed here [0], where vmlinux is
> deleted by Make because a subsequent step that consumes it as input
> throws an error.
> 
> So refactor the vmlinux shell scripts and build rules so that
> architectures that rely on --emit-relocs to construct vmlinux with
> static relocations preserved will get a separate vmlinux.unstripped file
> carrying those relocations. This removes the need for an imperative
> postlink step, given that any rules that depend on the unstripped
> vmlinux can now simply depend on vmlinux.unstripped, rather than inject
> a build step into Makefile.postlink

Nice! Does this also result in any measurable speedup of the build, or 
are the steps still similar?

But in terms of justification for upstreaming, the reduction in 
complexity alone makes it worth it IMO:

  19 files changed, 52 insertions(+), 87 deletions(-)

Thanks,

	Ingo

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Linus Torvalds]

On Mon, 24 Feb 2025 at 10:51, Ingo Molnar <mingo@kernel.org> wrote:
>
> But in terms of justification for upstreaming, the reduction in
> complexity alone makes it worth it IMO:
>
>   19 files changed, 52 insertions(+), 87 deletions(-)

Yeah, absolutely. Our fancy make build rules still have too many of
the phony forced targets, but this is a few less of them and makes the
build confirm (more) to the usual rules.

I do wonder if we could just get rid of that
CONFIG_ARCH_VMLINUX_NEEDS_RELOCS entirely and make it just be how all
architectures do it.

Yes, it was apparently "just" riscv/s390/x86/mips that did that
'strip_relocs' hack, but at the same time that whole pass *feels*
entirely generic.

IOW, this all makes me just wonder why other architectures don't do it?

              Linus

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Mon, 24 Feb 2025 at 21:00, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, 24 Feb 2025 at 10:51, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > But in terms of justification for upstreaming, the reduction in
> > complexity alone makes it worth it IMO:
> >
> >   19 files changed, 52 insertions(+), 87 deletions(-)
>
> Yeah, absolutely. Our fancy make build rules still have too many of
> the phony forced targets, but this is a few less of them and makes the
> build confirm (more) to the usual rules.
>
> I do wonder if we could just get rid of that
> CONFIG_ARCH_VMLINUX_NEEDS_RELOCS entirely and make it just be how all
> architectures do it.
>
> Yes, it was apparently "just" riscv/s390/x86/mips that did that
> 'strip_relocs' hack, but at the same time that whole pass *feels*
> entirely generic.
>

TL;DR it is not

It is only needed on architectures that use --emit-relocs in the first
place, e.g., to construct bespoke KASLR tables. This is actually a
somewhat dubious practice, because these are static relocations, i.e.,
what the linker consumes as input, and they are emitted along with
vmlinux as output. [*] This feature was (AFAIK) never really intended
for constructing dynamic relocation tables as some architectures in
Linux do.

On those architectures, these static relocations need to be stripped
again, to avoid bloating vmlinux with useless data.

On architectures that rely on PIE linking (such as arm64), the linker
will emit a dynamic relocation table that is more suitable for use at
boot time, i.e., it only contains absolute relocations (as
RIP-relative ones never require any fixing up at boot), and uses RELR
format to pack them very densely, removing the need for our own
special format.

Architectures that do not implement KASLR in the first place have no
need for these static relocations either.

PIE linking is generally a better choice than relying on
--emit-relocs, but it is highly ISA dependent whether that requires a
costlier kind of codegen. On arm64, we don't even bother generating
-fPIE code because ordinary code can be linked in PIE mode. OTOH, on
x86, we'd need full 64-bit PIC/PIE codegen in order to link with PIE,
whereas we currently rely on the 'kernel' code model to generate
32-bit wide absolute symbol references that can only refer to the top
2G of the 64-bit address space.

[*] Using static relocations to describe a fully linked binary such as
vmlinux is problematic because a) it covers all external symbol
references, including relative ones that don't need fixing up, but
more importantly, b) the linker may perform relaxations that result in
the code going out of sync with the relocation that annotates it (this
is not entirely avoidable if the relaxed version of the code cannot
even be described by any relocation specified by the ELF psABI)

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Mon, 24 Feb 2025 at 19:51, Ingo Molnar <mingo@kernel.org> wrote:
>
...
> >
> > So refactor the vmlinux shell scripts and build rules so that
> > architectures that rely on --emit-relocs to construct vmlinux with
> > static relocations preserved will get a separate vmlinux.unstripped file
> > carrying those relocations. This removes the need for an imperative
> > postlink step, given that any rules that depend on the unstripped
> > vmlinux can now simply depend on vmlinux.unstripped, rather than inject
> > a build step into Makefile.postlink
>
> Nice! Does this also result in any measurable speedup of the build, or
> are the steps still similar?
>

The steps are essentially the same, only described in a slightly
better way (and with an additional artifact so the used disk space
goes up slightly too)

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Mon, 24 Feb 2025 at 14:21, Ard Biesheuvel <ardb+git@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> Kbuild supports an architecture specific Makefile.postlink file that is
> invoked for the vmlinux target after it has been built. This Makefile
> takes 'vmlinux' (which has just been built) as the target, and mangles
> the file and/or constructs other intermediate artifacts from it.
>
> This violates the general philosophy of Make, which is based on rules
> and dependencies, and artifacts that are rebuilt only when any of their
> dependencies have been updated.
>
> Instead, the different incarnations of vmlinux that are consumed by
> different stages of the build should be emitted as distinct files, where
> rules and dependencies are used to define one in terms of the other.
>
> This also works around an error observed here [0], where vmlinux is
> deleted by Make because a subsequent step that consumes it as input
> throws an error.
>
> So refactor the vmlinux shell scripts and build rules so that
> architectures that rely on --emit-relocs to construct vmlinux with
> static relocations preserved will get a separate vmlinux.unstripped file
> carrying those relocations. This removes the need for an imperative
> postlink step, given that any rules that depend on the unstripped
> vmlinux can now simply depend on vmlinux.unstripped, rather than inject
> a build step into Makefile.postlink
>
> S390 should be able to do the same. MIPS and RISC-V perform some
> post-build checks on vmlinux, which is reasonable in principle for a
> postlink step, although deleting vmlinux when the check fails is equally
> unhelpful.
>
> [0] https://lore.kernel.org/all/Z5ARucnUgqjwBnrp@gmail.com/T/#m731ed0206949fc3f39fcc8a7b82fe348a8fc80c4
>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Ingo Molnar <mingo@kernel.org>
>
> Ard Biesheuvel (4):
>   Kbuild/link-vmlinux.sh: Make output file name configurable
>   Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations
>   Kbuild: Create intermediate vmlinux build with relocations preserved
>   x86: Get rid of Makefile.postlink
>

Ping?

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Masahiro Yamada]

On Fri, Mar 7, 2025 at 1:47 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 24 Feb 2025 at 14:21, Ard Biesheuvel <ardb+git@google.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@kernel.org>
> >
> > Kbuild supports an architecture specific Makefile.postlink file that is
> > invoked for the vmlinux target after it has been built. This Makefile
> > takes 'vmlinux' (which has just been built) as the target, and mangles
> > the file and/or constructs other intermediate artifacts from it.
> >
> > This violates the general philosophy of Make, which is based on rules
> > and dependencies, and artifacts that are rebuilt only when any of their
> > dependencies have been updated.
> >
> > Instead, the different incarnations of vmlinux that are consumed by
> > different stages of the build should be emitted as distinct files, where
> > rules and dependencies are used to define one in terms of the other.


In my understanding, the build rule of vmlinux is atomic
because vmlinux embeds a timestamp and a build version.

Now, you are splitting it into two stages.

vmlinux.unstripped (this includes timestamp and the build version)
  --(cmd_strip_relocs)-->  vmlinux


When cmd_strip_relocs is changed, only vmlinux is updated.
This changes the content of vmlinux, but its timestamp and build version
remain the same.

So, I am not sure if this is the right direction.


You can see more steps for updating vmlinux.
Do you believe the build rule should be further split into
more fine-grained stages?

For example,

vmlinux.pre-sort  (this includes timestamp and the build version)
   --(scripts/sortable)-->
vmlinux.unstripped
   --(cmd_strip_relocs)-->
vmlinux

But, again, even when sorttable is changed,
the timestamp and the build version remain the same.


Yeah, arch/*/Makefile.postlink is a crap
where arch maintainers build a fence
and start whatever they want to do.

If they completely disappear, I would love it.

However, this seems a partial clean-up
within the scope you are interested in.
(more specifically your motivation is because Linus pointed out
a failure in arch/x86/Makefile.postlink deleted vmlinux)






> > This also works around an error observed here [0], where vmlinux is
> > deleted by Make because a subsequent step that consumes it as input
> > throws an error.
> >
> > So refactor the vmlinux shell scripts and build rules so that
> > architectures that rely on --emit-relocs to construct vmlinux with
> > static relocations preserved will get a separate vmlinux.unstripped file
> > carrying those relocations. This removes the need for an imperative
> > postlink step, given that any rules that depend on the unstripped
> > vmlinux can now simply depend on vmlinux.unstripped, rather than inject
> > a build step into Makefile.postlink
> >
> > S390 should be able to do the same. MIPS and RISC-V perform some
> > post-build checks on vmlinux, which is reasonable in principle for a
> > postlink step, although deleting vmlinux when the check fails is equally
> > unhelpful.
> >
> > [0] https://lore.kernel.org/all/Z5ARucnUgqjwBnrp@gmail.com/T/#m731ed0206949fc3f39fcc8a7b82fe348a8fc80c4
> >
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: Ingo Molnar <mingo@kernel.org>
> >
> > Ard Biesheuvel (4):
> >   Kbuild/link-vmlinux.sh: Make output file name configurable
> >   Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations
> >   Kbuild: Create intermediate vmlinux build with relocations preserved
> >   x86: Get rid of Makefile.postlink
> >
>
> Ping?




-- 
Best Regards
Masahiro Yamada

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Fri, 7 Mar 2025 at 19:54, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Fri, Mar 7, 2025 at 1:47 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Mon, 24 Feb 2025 at 14:21, Ard Biesheuvel <ardb+git@google.com> wrote:
> > >
> > > From: Ard Biesheuvel <ardb@kernel.org>
> > >
> > > Kbuild supports an architecture specific Makefile.postlink file that is
> > > invoked for the vmlinux target after it has been built. This Makefile
> > > takes 'vmlinux' (which has just been built) as the target, and mangles
> > > the file and/or constructs other intermediate artifacts from it.
> > >
> > > This violates the general philosophy of Make, which is based on rules
> > > and dependencies, and artifacts that are rebuilt only when any of their
> > > dependencies have been updated.
> > >
> > > Instead, the different incarnations of vmlinux that are consumed by
> > > different stages of the build should be emitted as distinct files, where
> > > rules and dependencies are used to define one in terms of the other.
>
>
> In my understanding, the build rule of vmlinux is atomic
> because vmlinux embeds a timestamp and a build version.
>
> Now, you are splitting it into two stages.
>
> vmlinux.unstripped (this includes timestamp and the build version)
>   --(cmd_strip_relocs)-->  vmlinux
>
>
> When cmd_strip_relocs is changed, only vmlinux is updated.
> This changes the content of vmlinux, but its timestamp and build version
> remain the same.
>
> So, I am not sure if this is the right direction.
>

You are saying that, when we change the contents of the
cmd_strip_relocs build rule and rebuild without cleaning, vmlinux will
have an older timestamp? I think there are many more cases where the
version is not updated, so I don't see this as a problem at all.

>
> You can see more steps for updating vmlinux.
> Do you believe the build rule should be further split into
> more fine-grained stages?
>

No.

The problem is that vmlinux.relocs (in arch/x86/boot/compressed)
depends on vmlinux, but not the version of vmlinux that is ultimately
produced.

It should depend on an artifact that is always suitable to generate
the relocation table, not only during the short time between the
initial creation of vmlinux and the point during the execution of
Makefile.postlink where the relocations that are needed to generate
vmlinux.relocs are stripped from vmlinux.

> For example,
>
> vmlinux.pre-sort  (this includes timestamp and the build version)
>    --(scripts/sortable)-->

Why? Which other artifact depends on the unsorted tables, and can no
longer be generated correctly after the tables have been sorted?

> vmlinux.unstripped
>    --(cmd_strip_relocs)-->
> vmlinux
>
> But, again, even when sorttable is changed,
> the timestamp and the build version remain the same.
>

Again, there are many other ways in which the final vmlinux can be
newer than the internal version fields suggest. I really don't think
this is an issue.

>
> Yeah, arch/*/Makefile.postlink is a crap
> where arch maintainers build a fence
> and start whatever they want to do.
>
> If they completely disappear, I would love it.
>

Good.

> However, this seems a partial clean-up
> within the scope you are interested in.
> (more specifically your motivation is because Linus pointed out
> a failure in arch/x86/Makefile.postlink deleted vmlinux)
>

Yes. Makefile.postlink failures propagate back to the build rule that
generates vmlinux, and so the file is deleted again.

For sanity checks performed on vmlinux, this is fine. But for
generating another file that takes vmlinux as its input, this is
completely broken.

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Masahiro Yamada]

On Sat, Mar 8, 2025 at 7:49 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Fri, 7 Mar 2025 at 19:54, Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Fri, Mar 7, 2025 at 1:47 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Mon, 24 Feb 2025 at 14:21, Ard Biesheuvel <ardb+git@google.com> wrote:
> > > >
> > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > >
> > > > Kbuild supports an architecture specific Makefile.postlink file that is
> > > > invoked for the vmlinux target after it has been built. This Makefile
> > > > takes 'vmlinux' (which has just been built) as the target, and mangles
> > > > the file and/or constructs other intermediate artifacts from it.
> > > >
> > > > This violates the general philosophy of Make, which is based on rules
> > > > and dependencies, and artifacts that are rebuilt only when any of their
> > > > dependencies have been updated.
> > > >
> > > > Instead, the different incarnations of vmlinux that are consumed by
> > > > different stages of the build should be emitted as distinct files, where
> > > > rules and dependencies are used to define one in terms of the other.
> >
> >
> > In my understanding, the build rule of vmlinux is atomic
> > because vmlinux embeds a timestamp and a build version.
> >
> > Now, you are splitting it into two stages.
> >
> > vmlinux.unstripped (this includes timestamp and the build version)
> >   --(cmd_strip_relocs)-->  vmlinux
> >
> >
> > When cmd_strip_relocs is changed, only vmlinux is updated.
> > This changes the content of vmlinux, but its timestamp and build version
> > remain the same.
> >
> > So, I am not sure if this is the right direction.
> >
>
> You are saying that, when we change the contents of the
> cmd_strip_relocs build rule and rebuild without cleaning, vmlinux will
> have an older timestamp? I think there are many more cases where the
> version is not updated, so I don't see this as a problem at all.

For example please?


>
> >
> > You can see more steps for updating vmlinux.
> > Do you believe the build rule should be further split into
> > more fine-grained stages?
> >
>
> No.
>
> The problem is that vmlinux.relocs (in arch/x86/boot/compressed)
> depends on vmlinux, but not the version of vmlinux that is ultimately
> produced.

Why?

Is there any case where vmlinux and vmlinux.relocs become
out of sync?


> It should depend on an artifact that is always suitable to generate
> the relocation table, not only during the short time between the
> initial creation of vmlinux and the point during the execution of
> Makefile.postlink where the relocations that are needed to generate
> vmlinux.relocs are stripped from vmlinux.

I still do not understand why this is a problem.

arch/*/Makefile.postlink is invoked from
$(call if_changed_dep,link_vmlinux)

From Make's perspective, this is a single build rule
to generate vmlinux. For x86, vmlinux.relocs is
a byproduct. I do not see this as a problem.



> > For example,
> >
> > vmlinux.pre-sort  (this includes timestamp and the build version)
> >    --(scripts/sortable)-->
>
> Why? Which other artifact depends on the unsorted tables, and can no
> longer be generated correctly after the tables have been sorted?
>
> > vmlinux.unstripped
> >    --(cmd_strip_relocs)-->
> > vmlinux
> >
> > But, again, even when sorttable is changed,
> > the timestamp and the build version remain the same.
> >
>
> Again, there are many other ways in which the final vmlinux can be
> newer than the internal version fields suggest. I really don't think
> this is an issue.

Again, for example please.

The build rule of vmlinux is atomic.
When vmlinux is updated, its timestamp is updated.
When any part of the build rule fails, vmlinux is deleted
because we cannot keep an invalid vmlinux.
This process is quite simple.



>
> >
> > Yeah, arch/*/Makefile.postlink is a crap
> > where arch maintainers build a fence
> > and start whatever they want to do.
> >
> > If they completely disappear, I would love it.
> >
>
> Good.
>
> > However, this seems a partial clean-up
> > within the scope you are interested in.
> > (more specifically your motivation is because Linus pointed out
> > a failure in arch/x86/Makefile.postlink deleted vmlinux)
> >
>
> Yes. Makefile.postlink failures propagate back to the build rule that
> generates vmlinux, and so the file is deleted again.
>
> For sanity checks performed on vmlinux, this is fine. But for
> generating another file that takes vmlinux as its input, this is
> completely broken.

I do not think it is broken.
As I mentioned above, I regard vmlinux.relocs as a byproduct
of the atomic build rule of vmlinux. This works.



--
Best Regards
Masahiro Yamada

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
...
> I do not think it is broken.
> As I mentioned above, I regard vmlinux.relocs as a byproduct
> of the atomic build rule of vmlinux. This works.
>

There is no make rule for vmlinux.relocs, and so

- if it gets deleted, it cannot be rebuilt and even though the build
does not break, the relocation data is missing from the compressed
image, and this could potentially break the kaslr startup code,
- it vmlinux.relocs is older than vmlinux for some reason, make will
not notice and silently reuse the outdated version,
- when creating vmlinux.relocs from vmlinux and an error occurs,
vmlinux is deleted, making it difficult to diagnose the problem.

I think this is badly broken, but if you think this is all working as
it should, I am not going to debate this further, and you can consider
the patch series withdrawn.

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ingo Molnar]

* Ard Biesheuvel <ardb@kernel.org> wrote:

> On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> ...
> > I do not think it is broken.
> > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > of the atomic build rule of vmlinux. This works.

Except when it doesn't work, such as when an intermediate linking step 
fails, and intermediate build products are lost and cannot be recreated 
easily (or at all without modifying the source)?

And the thing is, there should be no such thing as an 'atomic build 
rule of vmlinux' if it means lost information when the build is broken 
at an intermediate step. What purpose does it have?

> There is no make rule for vmlinux.relocs, and so
> 
> - if it gets deleted, it cannot be rebuilt and even though the build
> does not break, the relocation data is missing from the compressed
> image, and this could potentially break the kaslr startup code,
> - it vmlinux.relocs is older than vmlinux for some reason, make will
> not notice and silently reuse the outdated version,
> - when creating vmlinux.relocs from vmlinux and an error occurs,
> vmlinux is deleted, making it difficult to diagnose the problem.
> 
> I think this is badly broken, but if you think this is all working as
> it should, I am not going to debate this further, and you can consider
> the patch series withdrawn.

That's very sad, as both the simplification is substantial:

  19 files changed, 52 insertions(+), 87 deletions(-)

and the increase in debuggability is substantial as well.

Thanks,

	Ingo

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Masahiro Yamada]

On Sun, Mar 9, 2025 at 6:48 PM Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Ard Biesheuvel <ardb@kernel.org> wrote:
>
> > On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > ...
> > > I do not think it is broken.
> > > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > > of the atomic build rule of vmlinux. This works.
>
> Except when it doesn't work, such as when an intermediate linking step
> fails, and intermediate build products are lost and cannot be recreated
> easily (or at all without modifying the source)?
>
> And the thing is, there should be no such thing as an 'atomic build
> rule of vmlinux' if it means lost information when the build is broken
> at an intermediate step. What purpose does it have?
>
> > There is no make rule for vmlinux.relocs, and so
> >
> > - if it gets deleted, it cannot be rebuilt and even though the build
> > does not break, the relocation data is missing from the compressed
> > image, and this could potentially break the kaslr startup code,
> > - it vmlinux.relocs is older than vmlinux for some reason, make will
> > not notice and silently reuse the outdated version,
> > - when creating vmlinux.relocs from vmlinux and an error occurs,
> > vmlinux is deleted, making it difficult to diagnose the problem.
> >
> > I think this is badly broken, but if you think this is all working as
> > it should, I am not going to debate this further, and you can consider
> > the patch series withdrawn.
>
> That's very sad, as both the simplification is substantial:
>
>   19 files changed, 52 insertions(+), 87 deletions(-)
>
> and the increase in debuggability is substantial as well.
>
> Thanks,
>
>         Ingo

When a byproduct is accidentally lost
(for example, manually deleted), it is not automatically restored.
Running 'rm vmlinux' or 'make clean' is needed.

vmlinux.relocs is one such byproduct.
Another is the map file when CONFIG_VMLINUX_MAP=y is enabled.

I am a bit concerned about having more and more
intermediate vmlinux.* files, but maybe only me.
I hope vmlinux.unstripped is the only/last one.


OK, let's do this.

Ard, please send v2 with .gitignore and 'clean' target updates.


--
Best Regards
Masahiro Yamada

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Ard Biesheuvel]

On Tue, 11 Mar 2025 at 03:39, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sun, Mar 9, 2025 at 6:48 PM Ingo Molnar <mingo@kernel.org> wrote:
> >
> >
> > * Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > > On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > >
> > > ...
> > > > I do not think it is broken.
> > > > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > > > of the atomic build rule of vmlinux. This works.
> >
> > Except when it doesn't work, such as when an intermediate linking step
> > fails, and intermediate build products are lost and cannot be recreated
> > easily (or at all without modifying the source)?
> >
> > And the thing is, there should be no such thing as an 'atomic build
> > rule of vmlinux' if it means lost information when the build is broken
> > at an intermediate step. What purpose does it have?
> >
> > > There is no make rule for vmlinux.relocs, and so
> > >
> > > - if it gets deleted, it cannot be rebuilt and even though the build
> > > does not break, the relocation data is missing from the compressed
> > > image, and this could potentially break the kaslr startup code,
> > > - it vmlinux.relocs is older than vmlinux for some reason, make will
> > > not notice and silently reuse the outdated version,
> > > - when creating vmlinux.relocs from vmlinux and an error occurs,
> > > vmlinux is deleted, making it difficult to diagnose the problem.
> > >
> > > I think this is badly broken, but if you think this is all working as
> > > it should, I am not going to debate this further, and you can consider
> > > the patch series withdrawn.
> >
> > That's very sad, as both the simplification is substantial:
> >
> >   19 files changed, 52 insertions(+), 87 deletions(-)
> >
> > and the increase in debuggability is substantial as well.
> >
> > Thanks,
> >
> >         Ingo
>
> When a byproduct is accidentally lost
> (for example, manually deleted), it is not automatically restored.
> Running 'rm vmlinux' or 'make clean' is needed.
>

Exactly. Make cannot detect this situation, and so the build breaks in some way.

> vmlinux.relocs is one such byproduct.
> Another is the map file when CONFIG_VMLINUX_MAP=y is enabled.
>

The linker map is not depended upon by other build targets, and is
typically for human debug consumption, so while not ideal, it is not
as broken as for the unstripped vmlinux.


> I am a bit concerned about having more and more
> intermediate vmlinux.* files, but maybe only me.
> I hope vmlinux.unstripped is the only/last one.
>

Maybe we should not strip vmlinux at all, but only remove any static
relocations when packaging? E.g., tar-pkg, etc

>
> OK, let's do this.
>
> Ard, please send v2 with .gitignore and 'clean' target updates.
>

Thanks, I'll prepare a v2, but in the meantime, can we think about not
removing the relocations in the first place?

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Masahiro Yamada]

On Tue, Mar 11, 2025 at 3:40 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Tue, 11 Mar 2025 at 03:39, Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Sun, Mar 9, 2025 at 6:48 PM Ingo Molnar <mingo@kernel.org> wrote:
> > >
> > >
> > > * Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > > On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > >
> > > > ...
> > > > > I do not think it is broken.
> > > > > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > > > > of the atomic build rule of vmlinux. This works.
> > >
> > > Except when it doesn't work, such as when an intermediate linking step
> > > fails, and intermediate build products are lost and cannot be recreated
> > > easily (or at all without modifying the source)?
> > >
> > > And the thing is, there should be no such thing as an 'atomic build
> > > rule of vmlinux' if it means lost information when the build is broken
> > > at an intermediate step. What purpose does it have?
> > >
> > > > There is no make rule for vmlinux.relocs, and so
> > > >
> > > > - if it gets deleted, it cannot be rebuilt and even though the build
> > > > does not break, the relocation data is missing from the compressed
> > > > image, and this could potentially break the kaslr startup code,
> > > > - it vmlinux.relocs is older than vmlinux for some reason, make will
> > > > not notice and silently reuse the outdated version,
> > > > - when creating vmlinux.relocs from vmlinux and an error occurs,
> > > > vmlinux is deleted, making it difficult to diagnose the problem.
> > > >
> > > > I think this is badly broken, but if you think this is all working as
> > > > it should, I am not going to debate this further, and you can consider
> > > > the patch series withdrawn.
> > >
> > > That's very sad, as both the simplification is substantial:
> > >
> > >   19 files changed, 52 insertions(+), 87 deletions(-)
> > >
> > > and the increase in debuggability is substantial as well.
> > >
> > > Thanks,
> > >
> > >         Ingo
> >
> > When a byproduct is accidentally lost
> > (for example, manually deleted), it is not automatically restored.
> > Running 'rm vmlinux' or 'make clean' is needed.
> >
>
> Exactly. Make cannot detect this situation, and so the build breaks in some way.
>
> > vmlinux.relocs is one such byproduct.
> > Another is the map file when CONFIG_VMLINUX_MAP=y is enabled.
> >
>
> The linker map is not depended upon by other build targets, and is
> typically for human debug consumption, so while not ideal, it is not
> as broken as for the unstripped vmlinux.
>
>
> > I am a bit concerned about having more and more
> > intermediate vmlinux.* files, but maybe only me.
> > I hope vmlinux.unstripped is the only/last one.
> >
>
> Maybe we should not strip vmlinux at all, but only remove any static
> relocations when packaging? E.g., tar-pkg, etc
> >
> > OK, let's do this.
> >
> > Ard, please send v2 with .gitignore and 'clean' target updates.
> >
>
> Thanks, I'll prepare a v2, but in the meantime, can we think about not
> removing the relocations in the first place?

OK, let's try this approach.


--
Best Regards
Masahiro Yamada

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Petr Pavlu]

On 3/11/25 07:40, Ard Biesheuvel wrote:
> On Tue, 11 Mar 2025 at 03:39, Masahiro Yamada <masahiroy@kernel.org> wrote:
>> I am a bit concerned about having more and more
>> intermediate vmlinux.* files, but maybe only me.
>> I hope vmlinux.unstripped is the only/last one.
>>
> 
> Maybe we should not strip vmlinux at all, but only remove any static
> relocations when packaging? E.g., tar-pkg, etc

Distributions typically have their own package recipes. The idea of
stripping these relocations from vmlinux in one place was that everyone
would trivially benefit from it. I'm not sure what you have exactly in
mind implementation-wise here, but I think this would be useful to keep.

-- 
Thanks,
Petr

Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

[Masahiro Yamada]

On Tue, Mar 11, 2025 at 3:40 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Tue, 11 Mar 2025 at 03:39, Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Sun, Mar 9, 2025 at 6:48 PM Ingo Molnar <mingo@kernel.org> wrote:
> > >
> > >
> > > * Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > > On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > >
> > > > ...
> > > > > I do not think it is broken.
> > > > > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > > > > of the atomic build rule of vmlinux. This works.
> > >
> > > Except when it doesn't work, such as when an intermediate linking step
> > > fails, and intermediate build products are lost and cannot be recreated
> > > easily (or at all without modifying the source)?
> > >
> > > And the thing is, there should be no such thing as an 'atomic build
> > > rule of vmlinux' if it means lost information when the build is broken
> > > at an intermediate step. What purpose does it have?
> > >
> > > > There is no make rule for vmlinux.relocs, and so
> > > >
> > > > - if it gets deleted, it cannot be rebuilt and even though the build
> > > > does not break, the relocation data is missing from the compressed
> > > > image, and this could potentially break the kaslr startup code,
> > > > - it vmlinux.relocs is older than vmlinux for some reason, make will
> > > > not notice and silently reuse the outdated version,
> > > > - when creating vmlinux.relocs from vmlinux and an error occurs,
> > > > vmlinux is deleted, making it difficult to diagnose the problem.
> > > >
> > > > I think this is badly broken, but if you think this is all working as
> > > > it should, I am not going to debate this further, and you can consider
> > > > the patch series withdrawn.
> > >
> > > That's very sad, as both the simplification is substantial:
> > >
> > >   19 files changed, 52 insertions(+), 87 deletions(-)
> > >
> > > and the increase in debuggability is substantial as well.
> > >
> > > Thanks,
> > >
> > >         Ingo
> >
> > When a byproduct is accidentally lost
> > (for example, manually deleted), it is not automatically restored.
> > Running 'rm vmlinux' or 'make clean' is needed.
> >
>
> Exactly. Make cannot detect this situation, and so the build breaks in some way.
>
> > vmlinux.relocs is one such byproduct.
> > Another is the map file when CONFIG_VMLINUX_MAP=y is enabled.
> >
>
> The linker map is not depended upon by other build targets, and is
> typically for human debug consumption, so while not ideal, it is not
> as broken as for the unstripped vmlinux.

Now you learned this statement is wrong.


-- 
Best Regards
Masahiro Yamada