[PATCH v2 11/28] kbuild: lto: postpone objtool

Sami Tolvanen
2020-09-03T20:38:05Z

With LTO, LLVM bitcode won't be compiled into native code until
modpost_link, or modfinal for modules. This change postpones calls
to objtool until after these steps.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
arch/Kconfig | 2 +-
scripts/Makefile.build | 2 ++
scripts/Makefile.modfinal | 24 ++++++++++++++++++++++--
scripts/link-vmlinux.sh | 23 ++++++++++++++++++++++-
4 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 71392e4a8900..7a418907e686 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -599,7 +599,7 @@ config LTO_CLANG
depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
depends on ARCH_SUPPORTS_LTO_CLANG
- depends on !FTRACE_MCOUNT_RECORD
+ depends on HAVE_OBJTOOL_MCOUNT || !(X86_64 && DYNAMIC_FTRACE)
depends on !KASAN
depends on !GCOV_KERNEL
select LTO
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index c348e6d6b436..b8f1f0d65a73 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -218,6 +218,7 @@ cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)),
endif # USE_RECORDMCOUNT

ifdef CONFIG_STACK_VALIDATION
+ifndef CONFIG_LTO_CLANG
ifneq ($(SKIP_STACK_VALIDATION),1)

__objtool_obj := $(objtree)/tools/objtool/objtool
@@ -253,6 +254,7 @@ objtool_obj = $(if $(patsubst y%,, \
$(__objtool_obj))

endif # SKIP_STACK_VALIDATION
+endif # CONFIG_LTO_CLANG
endif # CONFIG_STACK_VALIDATION

# Rebuild all objects when objtool changes, or is enabled/disabled.
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 1005b147abd0..909bd509edb4 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -34,10 +34,30 @@ ifdef CONFIG_LTO_CLANG
# With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to
# avoid a second slow LTO link
prelink-ext := .lto
-endif
+
+# ELF processing was skipped earlier because we didn't have native code,
+# so let's now process the prelinked binary before we link the module.
+
+ifdef CONFIG_STACK_VALIDATION
+ifneq ($(SKIP_STACK_VALIDATION),1)
+cmd_ld_ko_o += \
+ $(objtree)/tools/objtool/objtool \
+ $(if $(CONFIG_UNWINDER_ORC),orc generate,check) \
+ --module \
+ $(if $(CONFIG_FRAME_POINTER),,--no-fp) \
+ $(if $(CONFIG_GCOV_KERNEL),--no-unreachable,) \
+ $(if $(CONFIG_RETPOLINE),--retpoline,) \
+ $(if $(CONFIG_X86_SMAP),--uaccess,) \
+ $(if $(USE_OBJTOOL_MCOUNT),--mcount,) \
+ $(@:.ko=$(prelink-ext).o);
+
+endif # SKIP_STACK_VALIDATION
+endif # CONFIG_STACK_VALIDATION
+
+endif # CONFIG_LTO_CLANG

quiet_cmd_ld_ko_o = LD [M] $@
- cmd_ld_ko_o = \
+ cmd_ld_ko_o += \
$(LD) -r $(KBUILD_LDFLAGS) \
$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
$(addprefix -T , $(KBUILD_LDS_MODULE)) \
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 3e99a19b9195..a352a5ad9ef7 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -93,8 +93,29 @@ objtool_link()
{
local objtoolopt;

+ if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then
+ # Don't perform vmlinux validation unless explicitly requested,
+ # but run objtool on vmlinux.o now that we have an object file.
+ if [ -n "${CONFIG_UNWINDER_ORC}" ]; then
+ objtoolopt="orc generate"
+ else
+ objtoolopt="check"
+ fi
+
+ if [ -n ${USE_OBJTOOL_MCOUNT} ]; then
+ objtoolopt="${objtoolopt} --mcount"
+ fi
+ fi
+
if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then
- objtoolopt="check --vmlinux"
+ if [ -z "${objtoolopt}" ]; then
+ objtoolopt="check --vmlinux"
+ else
+ objtoolopt="${objtoolopt} --vmlinux"
+ fi
+ fi
+
+ if [ -n "${objtoolopt}" ]; then
if [ -z "${CONFIG_FRAME_POINTER}" ]; then
objtoolopt="${objtoolopt} --no-fp"
fi
--
2.28.0.402.g5ffc5be6b7-goog