[tip: x86/core] arch: Introduce CONFIG_FUNCTION_ALIGNMENT

tip-bot2 for Peter Zijlstra
2022-10-17T14:59:18Z

The following commit has been merged into the x86/core branch of tip:

Commit-ID: d49a0626216b95cd4bf696f6acf55f39a16ab0bb
Gitweb: https://git.kernel.org/tip/d49a0626216b95cd4bf696f6acf55f39a16ab0bb
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 15 Sep 2022 13:10:47 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 17 Oct 2022 16:40:58 +02:00

arch: Introduce CONFIG_FUNCTION_ALIGNMENT

Generic function-alignment infrastructure.

Architectures can select FUNCTION_ALIGNMENT_xxB symbols; the
FUNCTION_ALIGNMENT symbol is then set to the largest such selected
size, 0 otherwise.

>From this the -falign-functions compiler argument and __ALIGN macro
are set.

This incorporates the DEBUG_FORCE_FUNCTION_ALIGN_64B knob and future
alignment requirements for x86_64 (later in this series) into a single
place.

NOTE: also removes the 0x90 filler byte from the generic __ALIGN
primitive, that value makes no sense outside of x86.

NOTE: .balign 0 reverts to a no-op.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111143.719248727@infradead.org
---
Makefile | 4 ++--
arch/Kconfig | 24 ++++++++++++++++++++++++
arch/ia64/Kconfig | 1 +
arch/ia64/Makefile | 2 +-
arch/x86/Kconfig | 2 ++
arch/x86/boot/compressed/head_64.S | 8 ++++++++
arch/x86/include/asm/linkage.h | 4 +---
include/asm-generic/vmlinux.lds.h | 4 ++--
include/linux/linkage.h | 4 ++--
lib/Kconfig.debug | 1 +
10 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index f41ec8c..141e1bc 100644
--- a/Makefile
+++ b/Makefile
@@ -1004,8 +1004,8 @@ KBUILD_CFLAGS += $(CC_FLAGS_CFI)
export CC_FLAGS_CFI
endif

-ifdef CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B
-KBUILD_CFLAGS += -falign-functions=64
+ifneq ($(CONFIG_FUNCTION_ALIGNMENT),0)
+KBUILD_CFLAGS += -falign-functions=$(CONFIG_FUNCTION_ALIGNMENT)
endif

# arch Makefile may override CC so keep this after arch Makefile is included
diff --git a/arch/Kconfig b/arch/Kconfig
index 8f138e5..4025802 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1428,4 +1428,28 @@ source "kernel/gcov/Kconfig"

source "scripts/gcc-plugins/Kconfig"

+config FUNCTION_ALIGNMENT_4B
+ bool
+
+config FUNCTION_ALIGNMENT_8B
+ bool
+
+config FUNCTION_ALIGNMENT_16B
+ bool
+
+config FUNCTION_ALIGNMENT_32B
+ bool
+
+config FUNCTION_ALIGNMENT_64B
+ bool
+
+config FUNCTION_ALIGNMENT
+ int
+ default 64 if FUNCTION_ALIGNMENT_64B
+ default 32 if FUNCTION_ALIGNMENT_32B
+ default 16 if FUNCTION_ALIGNMENT_16B
+ default 8 if FUNCTION_ALIGNMENT_8B
+ default 4 if FUNCTION_ALIGNMENT_4B
+ default 0
+
endmenu
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index c6e06cd..d7e4a24 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -63,6 +63,7 @@ config IA64
select NUMA if !FLATMEM
select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
select ZONE_DMA32
+ select FUNCTION_ALIGNMENT_32B
default y
help
The Itanium Processor Family is Intel's 64-bit successor to
diff --git a/arch/ia64/Makefile b/arch/ia64/Makefile
index 56c4bb2..d553ab7 100644
--- a/arch/ia64/Makefile
+++ b/arch/ia64/Makefile
@@ -23,7 +23,7 @@ KBUILD_AFLAGS_KERNEL := -mconstant-gp
EXTRA :=

cflags-y := -pipe $(EXTRA) -ffixed-r13 -mfixed-range=f12-f15,f32-f127 \
- -falign-functions=32 -frename-registers -fno-optimize-sibling-calls
+ -frename-registers -fno-optimize-sibling-calls
KBUILD_CFLAGS_KERNEL := -mconstant-gp

GAS_STATUS = $(shell $(srctree)/arch/ia64/scripts/check-gas "$(CC)" "$(OBJDUMP)")
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6d1879e..f408fa8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -290,6 +290,8 @@ config X86
select X86_FEATURE_NAMES if PROC_FS
select PROC_PID_ARCH_STATUS if PROC_FS
select HAVE_ARCH_NODE_DEV_GROUP if X86_SGX
+ select FUNCTION_ALIGNMENT_16B if X86_64 || X86_ALIGNMENT_16
+ select FUNCTION_ALIGNMENT_4B
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index d33f060..190b803 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -38,6 +38,14 @@
#include "pgtable.h"

/*
+ * Fix alignment at 16 bytes. Following CONFIG_FUNCTION_ALIGNMENT will result
+ * in assembly errors due to trying to move .org backward due to the excessive
+ * alignment.
+ */
+#undef __ALIGN
+#define __ALIGN .balign 16, 0x90
+
+/*
* Locally defined symbols should be marked hidden:
*/
.hidden _bss
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index f484d65..9ee0e28 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -14,10 +14,8 @@

#ifdef __ASSEMBLY__

-#if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
-#define __ALIGN .p2align 4, 0x90
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT, 0x90;
#define __ALIGN_STR __stringify(__ALIGN)
-#endif

#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
#define RET jmp __x86_return_thunk
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c15de16..335b571 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -81,8 +81,8 @@
#define RO_EXCEPTION_TABLE
#endif

-/* Align . to a 8 byte boundary equals to maximum function alignment. */
-#define ALIGN_FUNCTION() . = ALIGN(8)
+/* Align . function alignment. */
+#define ALIGN_FUNCTION() . = ALIGN(CONFIG_FUNCTION_ALIGNMENT)

/*
* LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections, which
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index 1feab61..5c8865b 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -69,8 +69,8 @@
#endif

#ifndef __ALIGN
-#define __ALIGN .align 4,0x90
-#define __ALIGN_STR ".align 4,0x90"
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT
+#define __ALIGN_STR __stringify(__ALIGN)
#endif

#ifdef __ASSEMBLY__
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 3fc7abf..e90dc67 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -467,6 +467,7 @@ config SECTION_MISMATCH_WARN_ONLY
config DEBUG_FORCE_FUNCTION_ALIGN_64B
bool "Force all function address 64B aligned"
depends on EXPERT && (X86_64 || ARM64 || PPC32 || PPC64 || ARC)
+ select FUNCTION_ALIGNMENT_64B
help
There are cases that a commit from one domain changes the function
address alignment of other domains, and cause magic performance