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Message-ID: <4d2f1ada-2f31-4b44-a30d-dbccb97feba1@yandex.ru>
Date: Mon, 24 Feb 2025 16:35:54 +0300
From: Ivan Trofimov <i.trofimow@...dex.ru>
To: musl@...ts.openwall.com
Subject: [PATCH] x86_64: Generate an eh-frame entry for syscall_cp
Some eBPF-based profilers (open-telemetry/opentelemetry-ebpf-profiler,
yandex/perforator, parca-dev/parca etc. at github.com) leverage eh-frame
section to unwind the stacks of native executables in kernel context.
This approach works pretty well most of the time, but sometimes fails to
unwind through hand-written assembly due to it missing cfi-* directives.
Usually it's not that big of a deal and doesn't change the whole picture
much, however with musl things are different, since these unwinders fail
to unwind syscalls back to userspace, as musl doesn't generate an
eh-frame entry for __syscall_cp function.
Imagine a flamegraph, where all (or most) of the syscalls are completely
out of place: this is the problem this patch aims to fix for x86-64.
Signed-off-by: Ivan Trofimov <i.trofimow@...dex.ru>
---
src/thread/x86_64/syscall_cp.s | 3 +++
1 file changed, 3 insertions(+)
diff --git a/src/thread/x86_64/syscall_cp.s b/src/thread/x86_64/syscall_cp.s
index 4f101716..296415d7 100644
--- a/src/thread/x86_64/syscall_cp.s
+++ b/src/thread/x86_64/syscall_cp.s
@@ -10,6 +10,7 @@
.hidden __syscall_cp_asm
.type __syscall_cp_asm,@function
__syscall_cp_asm:
+.cfi_startproc
__cp_begin:
mov (%rdi),%eax
@@ -29,3 +30,5 @@ __cp_end:
ret
__cp_cancel:
jmp __cancel
+
+.cfi_endproc
--
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