https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84908
--- Comment #13 from Andy Lutomirski <luto at kernel dot org> ---
I find this whole discussion very confusing. The problem has nothing to do
with relocations AFAICT. The problem is that gcc is (as requested) generating
retpolines, and it's set up to do it by calling __x86_indirect_thunk_*, and
those helpers don't exist in the vDSO.
I also think that static inlines have anything to do with it. Nor so I see why
any function attributes make any sense.
The trivial fix is:
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 261802b1cc50..8140176b8b41 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -74,7 +74,7 @@ CFL := $(PROFILING) -mcmodel=small -fPIC -O2
-fasynchronous-unwind-tables -m64 \
-fno-omit-frame-pointer -foptimize-sibling-calls \
-DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
-$(vobjs): KBUILD_CFLAGS := $(filter-out
$(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
+$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS)
$(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
#
# vDSO code runs in userspace and -pg doesn't help with profiling anyway.
@@ -138,6 +138,7 @@ KBUILD_CFLAGS_32 := $(filter-out
-mcmodel=kernel,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
+KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
but it might be better to use the internal thunk mechanism.
You said that Andi Kleen had a comment. Can you point me to it?
