On 2/6/2026 8:36 PM, Jens Remus wrote:
> From: Josh Poimboeuf <[email protected]>
>
> Enable sframe generation in the VDSO library so kernel and user space
> can unwind through it.
>
> SFrame isn't supported for x32 or x86-32. Discard .sframe sections for
> those VDSOs.
>
> [ Jens Remus: Add support for SFrame V3. Prevent GNU_SFRAME program
> table entry to empty .sframe section. ]
>
> Signed-off-by: Josh Poimboeuf <[email protected]>
> Signed-off-by: Steven Rostedt (Google) <[email protected]>
> Signed-off-by: Jens Remus <[email protected]>
> diff --git a/arch/Kconfig b/arch/Kconfig
> @@ -479,6 +479,13 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
> It uses the same command line parameters, and sysctl interface,
> as the generic hardlockup detectors.
>
> +config AS_SFRAME
> + bool
> +
> +config AS_SFRAME3
> + def_bool $(as-instr,.cfi_startproc\n.cfi_endproc,-Wa$(comma)--gsframe-3)
Above tests whether the assembler supports --gsframe-3 to generate
.sframe in SFrame V3 format. GNU assembler only supports to generate
SFrame for x86-64. If the assembler is built for i386 (x86-32) the test
will fail unless option --64 is specified. I wonder whether that could
happen in (the rather hypothetical?) case, when the kernel is cross built
for x86-64 on i386? Should this therefore be changed to the following?
config AS_SFRAME_64
def_bool $(as-instr,.cfi_startproc\n.cfi_endproc,$(m64-flag)
-Wa$(comma)--gsframe)
An alternative would be to enable as-instr64 to accept an optional flag
operand, similar to as-instr, and use as-instr64 instead of as-instr.
Or is this not required, as in a cross build for 64-bit on a 32-bit
platform (or inverse) a respective cross toolchain is a prerequisite and
the m64-flag (or m32-flag) is not used?
I tried to simulate this using docker and an i386 image and then using
the i386 tool in the container to switch "uname -m" to "i686". But both
of my following attempts to build for x86-64 on i386 fail with fixdep
not found:
$ docker run -it --rm -v "$HOME/linux:$HOME/linux" --platform i386
public.ecr.aws/docker/library/debian:13.3
# sed -i -s 's/^Types: deb/& deb-src/' /etc/apt/sources.list.d/debian.sources
# apt update
# apt -y build-dep linux
# make mrproper
# i386 make ARCH=x86_64 defconfig
# i386 make ARCH=x86_64 arch/x86/entry/vdso/
# make mrproper
# apt -y install gcc-x86-64-linux-gnu
# i386 make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- defconfig
# i386 make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- arch/x86/entry/vdso/
> + select AS_SFRAME
> +
> config UNWIND_USER
> bool
> diff --git a/arch/x86/entry/vdso/vdso64/Makefile
> b/arch/x86/entry/vdso/vdso64/Makefile
> @@ -14,6 +14,7 @@ vobjs-$(CONFIG_X86_SGX) += vsgx.o
>
> # Compilation flags
> flags-y := -DBUILD_VDSO64 -m64 -mcmodel=small
> +flags-$(CONFIG_AS_SFRAME3) += -Wa,--gsframe-3
flags-$(CONFIG_AS_SFRAME3_64) += -Wa,--gsframe-3
>
> # The location of this include matters!
> include $(src)/../common/Makefile.include
Thanks and regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
[email protected] / [email protected]
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