Commit 4ab7674f authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Peter Zijlstra
Browse files

objtool: Make jump label hack optional 



Objtool secretly does a jump label hack to overcome the limitations of
the toolchain.  Make the hack explicit (and optional for other arches)
by turning it into a cmdline option and kernel config option.

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/3bdcbfdd27ecb01ddec13c04bdf756a583b13d24.1650300597.git.jpoimboe@redhat.com
parent 26e17689

arch/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ config JUMP_LABEL 
	bool "Optimize very unlikely/likely branches"

	depends on HAVE_ARCH_JUMP_LABEL

	depends on CC_HAS_ASM_GOTO

	select OBJTOOL if HAVE_JUMP_LABEL_HACK

	help

	 This option enables a transparent branch optimization that

	 makes certain almost-always-true or almost-always-false branch
@@ -1031,6 +1032,9 @@ config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT 
config HAVE_OBJTOOL

	bool



config HAVE_JUMP_LABEL_HACK

	bool



config HAVE_STACK_VALIDATION

	bool

	help

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -212,6 +212,7 @@ config X86 
	select HAVE_IOREMAP_PROT

	select HAVE_IRQ_EXIT_ON_IRQ_STACK	if X86_64

	select HAVE_IRQ_TIME_ACCOUNTING

	select HAVE_JUMP_LABEL_HACK		if HAVE_OBJTOOL

	select HAVE_KERNEL_BZIP2

	select HAVE_KERNEL_GZIP

	select HAVE_KERNEL_LZ4

arch/x86/include/asm/jump_label.h

+3 −3
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ 
	_ASM_PTR "%c0 + %c1 - .\n\t"			\

	".popsection \n\t"



#ifdef CONFIG_OBJTOOL

#ifdef CONFIG_HAVE_JUMP_LABEL_HACK



static __always_inline bool arch_static_branch(struct static_key *key, bool branch)

{
@@ -34,7 +34,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran 
	return true;

}



#else /* !CONFIG_OBJTOOL */

#else /* !CONFIG_HAVE_JUMP_LABEL_HACK */



static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch)

{
@@ -48,7 +48,7 @@ static __always_inline bool arch_static_branch(struct static_key * const key, co 
	return true;

}



#endif /* CONFIG_OBJTOOL */

#endif /* CONFIG_HAVE_JUMP_LABEL_HACK */



static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch)

{

scripts/Makefile.build

+1 −0
Original line number Diff line number Diff line
@@ -227,6 +227,7 @@ ifdef CONFIG_OBJTOOL 
objtool := $(objtree)/tools/objtool/objtool



objtool_args =								\

	$(if $(CONFIG_HAVE_JUMP_LABEL_HACK), --hacks=jump_label)	\

	$(if $(CONFIG_X86_KERNEL_IBT), --lto --ibt)			\

	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\

	$(if $(CONFIG_UNWINDER_ORC), --orc)				\

scripts/link-vmlinux.sh

+4 −0
Original line number Diff line number Diff line
@@ -117,6 +117,10 @@ objtool_link() 
		# Don't perform vmlinux validation unless explicitly requested,

		# but run objtool on vmlinux.o now that we have an object file.



		if is_enabled CONFIG_HAVE_JUMP_LABEL_HACK; then

			objtoolopt="${objtoolopt} --hacks=jump_label"

		fi



		if is_enabled CONFIG_X86_KERNEL_IBT; then

			objtoolopt="${objtoolopt} --ibt"

		fi