Re: [PATCH v8 6/6] x86/vdso: Enable sframe generation in VDSO

On Tue, Feb 10, 2026 at 05:46:33PM +0100, Jens Remus wrote:

On 2/6/2026 8:36 PM, Jens Remus wrote:

quoted

From: Josh Poimboeuf <jpoimboe@kernel.org>

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 <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Jens Remus <redacted>

quoted

diff --git a/arch/Kconfig b/arch/Kconfig

quoted

@@ -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/

Hm, I think I broke that with

  a808a2b35f66 ("tools build: Fix fixdep dependencies")

... though it's been broken almost a year, maybe nobody cares.

Regardless, we do need to fix "make clean" and "make mrproper" for
objtool, which would be something like so:

diff --git a/Makefile b/Makefile
index d3a8482bdbd0..ed850044491d 100644
--- a/Makefile
+++ b/Makefile

@@ -1474,6 +1474,15 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
 	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
 endif
 
+PHONY += objtool_clean
+
+objtool_O = $(abspath $(objtree))/tools/objtool
+
+objtool_clean:
+ifneq ($(wildcard $(objtool_O)),)
+	$(Q)$(MAKE) -sC $(abs_srctree)/tools/objtool O=$(objtool_O) srctree=$(abs_srctree) clean
+endif
+
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
 	$(Q)$(MAKE) O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/

@@ -1637,7 +1646,7 @@ vmlinuxclean:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
 	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)
 
-clean: archclean vmlinuxclean resolve_btfids_clean
+clean: archclean vmlinuxclean resolve_btfids_clean objtool_clean
 
 # mrproper - Delete all generated files, including .config
 #

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index a40f30232929..6964175abdfd 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile

@@ -29,6 +29,8 @@ srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
 
+RM ?= rm -f
+
 LIBSUBCMD_DIR = $(srctree)/tools/lib/subcmd/
 ifneq ($(OUTPUT),)
   LIBSUBCMD_OUTPUT = $(abspath $(OUTPUT))/libsubcmd