[PATCH v6 6/6] x86/vdso: Enable sframe generation in VDSO

Jens Remus
2026-01-29T11:28:21Z

Enable sframe generation in the VDSO library so kernel and user space
can unwind through it.

[ 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 <jremus@linux.ibm.com>
---
arch/Kconfig | 7 +++++++
arch/x86/entry/vdso/Makefile | 10 +++++++---
arch/x86/entry/vdso/vdso-layout.lds.S | 7 +++++++
arch/x86/include/asm/dwarf2.h | 5 ++++-
4 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index dcb553136e0c..b5b3a83072f7 100644
--- 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)
+ select AS_SFRAME
+
config UNWIND_USER
bool

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index f247f5f5cb44..748e0a630e81 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -47,13 +47,17 @@ quiet_cmd_vdso2c = VDSO2C $@
$(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
$(call if_changed,vdso2c)

+ifeq ($(CONFIG_AS_SFRAME3),y)
+ SFRAME_CFLAGS := -Wa,--gsframe-3
+endif
+
#
# Don't omit frame pointers for ease of userspace debugging, but do
# optimize sibling calls.
#
CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
$(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
- -fno-omit-frame-pointer -foptimize-sibling-calls \
+ -fno-omit-frame-pointer $(SFRAME_CFLAGS) -foptimize-sibling-calls \
-DDISABLE_BRANCH_PROFILING -DBUILD_VDSO

ifdef CONFIG_MITIGATION_RETPOLINE
@@ -63,7 +67,7 @@ endif
endif

$(vobjs): KBUILD_CFLAGS := $(filter-out $(PADDING_CFLAGS) $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(RANDSTRUCT_CFLAGS) $(KSTACK_ERASE_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
-$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO
+$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO $(SFRAME_CFLAGS)

#
# vDSO code runs in userspace and -pg doesn't help with profiling anyway.
@@ -104,7 +108,7 @@ $(obj)/%-x32.o: $(obj)/%.o FORCE

targets += vdsox32.lds $(vobjx32s-y)

-$(obj)/%.so: OBJCOPYFLAGS := -S --remove-section __ex_table
+$(obj)/%.so: OBJCOPYFLAGS := -g --remove-section __ex_table
$(obj)/%.so: $(obj)/%.so.dbg FORCE
$(call if_changed,objcopy)

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 60747905de2b..acdc55435d99 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -59,6 +59,9 @@ SECTIONS
.eh_frame_hdr : { *(.eh_frame_hdr) } :text :eh_frame_hdr
.eh_frame : { KEEP (*(.eh_frame)) } :text

+#ifdef CONFIG_AS_SFRAME
+ .sframe : { *(.sframe) } :text :sframe
+#endif

/*
* Text is well-separated from actual data: there's plenty of
@@ -87,6 +90,7 @@ SECTIONS
* Very old versions of ld do not recognize this name token; use the constant.
*/
#define PT_GNU_EH_FRAME 0x6474e550
+#define PT_GNU_SFRAME 0x6474e554

/*
* We must supply the ELF program headers explicitly to get just one
@@ -98,4 +102,7 @@ PHDRS
dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
note PT_NOTE FLAGS(4); /* PF_R */
eh_frame_hdr PT_GNU_EH_FRAME;
+#ifdef CONFIG_AS_SFRAME
+ sframe PT_GNU_SFRAME;
+#endif
}
diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
index 65d958ef1178..ce294e6c9017 100644
--- a/arch/x86/include/asm/dwarf2.h
+++ b/arch/x86/include/asm/dwarf2.h
@@ -12,8 +12,11 @@
* For the vDSO, emit both runtime unwind information and debug
* symbols for the .dbg file.
*/
-
+#if defined(__x86_64__) && defined(CONFIG_AS_SFRAME)
+ .cfi_sections .eh_frame, .debug_frame, .sframe
+#else
.cfi_sections .eh_frame, .debug_frame
+#endif

#define CFI_STARTPROC .cfi_startproc
#define CFI_ENDPROC .cfi_endproc
--
2.51.0