linux-kernel - [RFC PATCH v2 06/15] s390/vdso: Keep function symbols in vDSO

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Message-ID: <20251205171446.2814872-7-jremus@linux.ibm.com>
Date: Fri,  5 Dec 2025 18:14:37 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...nel.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
        "Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
        Dylan Hatch <dylanbhatch@...gle.com>
Subject: [RFC PATCH v2 06/15] s390/vdso: Keep function symbols in vDSO

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@...ux.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