Re: [PATCH v3 06/19] x86/vdso: Enable sframe generation in VDSO

[Josh Poimboeuf]

On Wed, Oct 30, 2024 at 07:20:08PM +0100, Jens Remus wrote:
> > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > index c9216ac4fb1e..75ae9e093a2d 100644
> > --- a/arch/x86/entry/vdso/Makefile
> > +++ b/arch/x86/entry/vdso/Makefile
> > @@ -47,13 +47,15 @@ quiet_cmd_vdso2c = VDSO2C  $@
> >   $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> >   	$(call if_changed,vdso2c)
> > +SFRAME_CFLAGS := $(call as-option,-Wa$(comma)-gsframe,)
> 
> I have the impression this test might not work as expected.

I suspect it works fine on x86-64, since that was the first arch
supported, so --gsframe being supported also means x86-64 is supported.

But yeah, other arches (and x86-32) are a different story.

> Maybe the following would be an alternative test in the Makefile?
> 
> SFRAME_CFLAGS := $(call as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_SFRAME=1)
> ifneq ($(SFRAME_CFLAGS),)
>        SFRAME_CFLAGS += -Wa,--gsframe
> endif

Looks good, though the ifneq isn't needed:

SFRAME_CFLAGS := $(call as-instr, \
		   .cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc, \
		   Wa$(comma)--gsframe -DCONFIG_AS_SFRAME=1)


Though, if multiple arches are going to be using that, maybe it should
just be a config option:


diff --git a/arch/Kconfig b/arch/Kconfig
index 33449485eafd..676dd45a7255 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -446,6 +446,9 @@ config HAVE_UNWIND_USER_SFRAME
 	bool
 	select UNWIND_USER
 
+config AS_SFRAME
+	def_bool $(as-instr,.cfi_sections .sframe\n.cfi_startproc\n.cfi_endproc)
+
 config HAVE_PERF_CALLCHAIN_DEFERRED
 	bool