[RFC PATCH v3 07/17] s390/vdso: Keep function symbols in vDSO

Jens Remus
2025-12-08T17:16:33Z

Keep all function symbols in the vDSO .symtab for stack trace purposes.
This enables a stack tracer, such as perf, to lookup these function
symbols in addition to those already exported in vDSO .dynsym.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
Changes in RFC v2:
- Use objcopy flag "-g" instead of "-S" with the cumbersome filter
"-w -K "__arch_*" -K "__cvdso_*" -K "__s390_vdso_*" to keep the
function symbols, as Josh did in "x86/vdso: Enable sframe
generation in VDSO":
https://lore.kernel.org/all/20250425024023.173709192@goodmis.org/
- Reword commit message.

Note that unlike Josh I did not squash this into the subsequent patch
"s390/vdso: Enable SFrame generation in vDSO", as this change is
unrelated to enabling the use of SFrame. perf report/script do also
benefit from this change when using perf record --call-graph dwarf.

Note that this change does not cause the vDSO build-id to change.
perf record may therefore not dump an updated copy of the vDSO to
~/.debug/[vdso]/<build-id>/vdso, so that perf report/script may
use a stale copy without .symtab. Resolve by deleting ~/.debug/.

arch/s390/kernel/vdso64/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
index d8f0df742809..8e78dc3ba025 100644
--- a/arch/s390/kernel/vdso64/Makefile
+++ b/arch/s390/kernel/vdso64/Makefile
@@ -53,7 +53,7 @@ $(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) $(obj-cvdso64) FORCE
$(call if_changed,vdso_and_check)

# strip rule for the .so file
-$(obj)/%.so: OBJCOPYFLAGS := -S
+$(obj)/%.so: OBJCOPYFLAGS := -g
$(obj)/%.so: $(obj)/%.so.dbg FORCE
$(call if_changed,objcopy)

--
2.51.0