On Tue, 18 Aug 2026 16:49:29 +0200
Jens Remus <[email protected]> wrote:
> This series adds support for parsing DWARF Call Frame Information (CFI)
> from the .eh_frame_hdr and .eh_frame sections of user space ELF files.
Very nice! I don't have time this week to look at it, but I just
applied the series and tried it out with:
perf record --call-graph fp,defer trace-cmd report ~/trace.dat
And did a: perf -D script
And found this:
264990534603 0x19370 [0x78]: PERF_RECORD_CALLCHAIN_DEFERRED(IP, 0x2):
1165/1165: 0x105700000005
... FP chain: nr:10
..... 0: 00007f5feafd362a
..... 1: 00007f5feb249781
..... 2: 00007f5feb2498de
..... 3: 000055935526fbdc
..... 4: 00005593552649e6
..... 5: 000055935523c2d0
..... 6: 000055935523d24c
..... 7: 0000559355227bfe
..... 8: 00007f5feaef9f75
..... 9: 00007ffdaf879d38
... thread: trace-cmd:1165
...... dso: /proc/kcore
trace-cmd 1165 264.990473: 395990 cpu/cycles/P:
ffffffff8477d8d3 check_preemption_disabled+0x13 ([kernel.kallsyms])
ffffffff819aa495 rcu_is_watching+0x15 ([kernel.kallsyms])
ffffffff816dbcff unwind_next_frame+0x45f ([kernel.kallsyms])
ffffffff81642e91 arch_stack_walk+0xa1 ([kernel.kallsyms])
ffffffff81a2e633 stack_trace_save+0x93 ([kernel.kallsyms])
ffffffff82251210 kasan_save_stack+0x30 ([kernel.kallsyms])
ffffffff822541b0 kasan_record_aux_stack+0xb0 ([kernel.kallsyms])
ffffffff819c1e2a __call_rcu_common+0xca ([kernel.kallsyms])
ffffffff821be05f kmem_cache_free+0x2ef ([kernel.kallsyms])
ffffffff8233e4a7 vfs_fstatat+0x57 ([kernel.kallsyms])
ffffffff8233e573 __do_sys_newfstatat+0x83 ([kernel.kallsyms])
ffffffff84772a8e do_syscall_64+0x7e ([kernel.kallsyms])
ffffffff8100012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])
7f5feafd362a __GI___fstatat64+0xa
(/usr/lib/x86_64-linux-gnu/libc.so.6)
7f5feb249781 tep_load_plugins_hook+0xd1
(/usr/local/lib64/libtraceevent.so.1.9.0)
7f5feb2498de tep_load_plugins+0x35
(/usr/local/lib64/libtraceevent.so.1.9.0)
55935526fbdc tcmd_load_plugins+0x85 (/usr/local/bin/trace-cmd)
5593552649e6 tracecmd_alloc_fd+0x2da (/usr/local/bin/trace-cmd)
55935523c2d0 read_trace_header+0x62 (/usr/local/bin/trace-cmd)
55935523d24c trace_report+0x869 (/usr/local/bin/trace-cmd)
559355227bfe main+0x90 (/usr/local/bin/trace-cmd)
7f5feaef9f75 __libc_start_call_main+0x75
(/usr/lib/x86_64-linux-gnu/libc.so.6)
7ffdaf879d38 [unknown] ([unknown])
I injected trace_printk() into the code to make sure it was using the
eh_frame unwinding:
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 85fc82252af1..585f022bcabe 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -200,6 +200,7 @@ static int unwind_user_next(struct unwind_user_state *state)
case UNWIND_USER_TYPE_EH_FRAME:
switch (unwind_user_next_eh_frame(state)) {
case 0:
+ trace_printk("USE EH_FRAME\n");
return 0;
case -ENOENT:
continue; /* Try next method. */
@@ -208,8 +209,9 @@ static int unwind_user_next(struct unwind_user_state *state)
}
break;
case UNWIND_USER_TYPE_FP:
- if (!unwind_user_next_fp(state))
- return 0;
+ if (!unwind_user_next_fp(state)) {
+ trace_printk("USE FRAME POINTER\n");
+ return 0; }
continue;
default:
WARN_ONCE(1, "Undefined unwind bit %d", bit);
And have this:
# trace-cmd show
[..]
trace-cmd-1136 [001] ..... 239.482498: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482501: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482504: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482507: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482821: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482825: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482828: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482831: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.482834: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483004: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483007: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483010: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483013: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483016: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483230: unwind_user: USE FRAME
POINTER
trace-cmd-1136 [001] ..... 239.483234: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483238: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483240: unwind_user: USE EH_FRAME
trace-cmd-1136 [001] ..... 239.483243: unwind_user: USE EH_FRAME
[..]
Note, the compile had one warning (with all patches applied):
vmlinux.o: warning: objtool: eh_frame_find+0x270c: call to
eh_frame_do_expression.isra.0() with UACCESS enabled
I'll try to get time when I get back from my travels next week to look
at each of the patches.
I also do not think this makes sframe obsolete. I believe there's holes
with eh_frame and some may not like the complexity of it. But this
gives us an honest look at what options are available to us.
Thanks for doing this!
-- Steve
