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Message-ID: <c8fef007dd694d0993cd007c44f458ff@huawei.com>
Date: Mon, 22 Jul 2024 12:19:31 +0000
From: duchangbin <changbin.du@...wei.com>
To: Adrian Hunter <adrian.hunter@...el.com>
CC: duchangbin <changbin.du@...wei.com>, Peter Zijlstra
<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Arnaldo Carvalho de
Melo" <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Nathan
Chancellor <nathan@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa
<jolsa@...nel.org>, "Ian Rogers" <irogers@...gle.com>, "Liang, Kan"
<kan.liang@...ux.intel.com>, "Nick Desaulniers" <ndesaulniers@...gle.com>,
Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>, "Wanghui (OS Kernel Lab,
Beijing)" <hw.huiwang@...wei.com>
Subject: Re: [PATCH v5 1/8] perf: support specify vdso path in cmdline
On Thu, Jul 18, 2024 at 08:02:16PM +0300, Adrian Hunter wrote:
> On 2/07/24 07:18, Changbin Du wrote:
> > The vdso dumped from process memory (in buildid-cache) lacks debugging
> > info. To annotate vdso symbols with source lines we need specify a
> > debugging version.
> >
> > For x86, we can find them from your local build as
> > arch/x86/entry/vdso/vdso{32,64}.so.dbg. Or they may reside in
> > /lib/modules/<version>/vdso/vdso{32,64}.so on Ubuntu. But notice that
> > the buildid has to match.
> >
> > $ sudo perf record -a
> > $ sudo perf report --objdump=llvm-objdump \
> > --vdso arch/x86/entry/vdso/vdso64.so.dbg,arch/x86/entry/vdso/vdso32.so.dbg
> >
> > Samples: 17K of event 'cycles:P', 4000 Hz, Event count (approx.): 1760
> > __vdso_clock_gettime /work/linux-host/arch/x86/entry/vdso/vdso64.so.d
> > Percent│ movq -48(%rbp),%rsi
> > │ testq %rax,%rax
> > │ ; return vread_hvclock();
> > │ movq %rax,%rdx
> > │ ; if (unlikely(!vdso_cycles_ok(cycles)))
> > │ ↑ js eb
> > │ ↑ jmp 74
> > │ ; ts->tv_sec = vdso_ts->sec;
> > 0.02 │147: leaq 2(%rbx),%rax
> > │ shlq $4, %rax
> > │ addq %r10,%rax
> > │ ; while ((seq = READ_ONCE(vd->seq)) & 1) {
> > 9.38 │152: movl (%r10),%ecx
> >
> > When doing cross platform analysis, we also need specify the vdso path if
> > we are interested in its symbols.
> >
>
> Just realized this is about objdump. Sorry for not getting that
> earlier.
>
> Like perf tools, objdump follows the paradigm of attempting to
> locate and use debug info transparently. However, objdump looks
> at the installed debug info in /usr/lib/debug/.build-id/
>
> For example, if the debug file is copied (or linked) there, then
> objdump or llvm-objdump will find it:
>
> $ llvm-objdump-18 -dS ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso | head -20
>
> ~/.debug/[vdso]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 00000000000006d0 <.text>:
> 6d0: 48 8d 3d 29 d9 ff ff leaq -0x26d7(%rip), %rdi # 0xffffffffffffe000
> 6d7: eb 19 jmp 0x6f2 <.text+0x22>
> 6d9: 4c 8b 0d 28 d9 ff ff movq -0x26d8(%rip), %r9 # 0xffffffffffffe008
> 6e0: 4c 8b 05 29 d9 ff ff movq -0x26d7(%rip), %r8 # 0xffffffffffffe010
> 6e7: 0f 01 f9 rdtscp
> 6ea: 66 90 nop
> 6ec: 8b 0f movl (%rdi), %ecx
> 6ee: 39 ce cmpl %ecx, %esi
> 6f0: 74 0e je 0x700 <.text+0x30>
> 6f2: 8b 37 movl (%rdi), %esi
> 6f4: 85 f6 testl %esi, %esi
> 6f6: 75 e1 jne 0x6d9 <.text+0x9>
> 6f8: 48 c7 c0 ff ff ff ff movq $-0x1, %rax
> 6ff: c3 retq
> $ sudo ln -s /lib/modules/6.9.2-local/build/arch/x86/entry/vdso/vdso64.so.dbg /usr/lib/debug/.build-id/cf/702469f4637840fd6ba1a8d8a628ff83253d04.debug
> $ llvm-objdump-18 -dS ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso | head -20
>
> ~/.debug/[vdso]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 00000000000006d0 <vread_hvclock>:
> ; hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
> 6d0: 48 8d 3d 29 d9 ff ff leaq -0x26d7(%rip), %rdi # 0xffffffffffffe000 <hvclock_page>
> 6d7: eb 19 jmp 0x6f2 <vread_hvclock+0x22>
> ; scale = READ_ONCE(tsc_pg->tsc_scale);
> 6d9: 4c 8b 0d 28 d9 ff ff movq -0x26d8(%rip), %r9 # 0xffffffffffffe008 <hvclock_page+0x8>
> ; offset = READ_ONCE(tsc_pg->tsc_offset);
> 6e0: 4c 8b 05 29 d9 ff ff movq -0x26d7(%rip), %r8 # 0xffffffffffffe010 <hvclock_page+0x10>
> ; asm volatile(ALTERNATIVE_2("rdtsc",
> 6e7: 0f 31 rdtsc
> 6e9: 90 nop
> 6ea: 90 nop
> 6eb: 90 nop
> ; } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
> 6ec: 8b 0f movl (%rdi), %ecx
> $
>
> Would that solve your problem?
>
> Notably, later versions of llvm-objdump have an option
> --debug-file-directory which makes it possible to
> have the debug info in a directory owned by the user,
> for example:
>
> $ sudo rm /usr/lib/debug/.build-id/cf/702469f4637840fd6ba1a8d8a628ff83253d04.debug
> $ llvm-objdump-18 -dS ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso | head -20
>
> ~/.debug/[vdso]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 00000000000006d0 <.text>:
> 6d0: 48 8d 3d 29 d9 ff ff leaq -0x26d7(%rip), %rdi # 0xffffffffffffe000
> 6d7: eb 19 jmp 0x6f2 <.text+0x22>
> 6d9: 4c 8b 0d 28 d9 ff ff movq -0x26d8(%rip), %r9 # 0xffffffffffffe008
> 6e0: 4c 8b 05 29 d9 ff ff movq -0x26d7(%rip), %r8 # 0xffffffffffffe010
> 6e7: 0f 01 f9 rdtscp
> 6ea: 66 90 nop
> 6ec: 8b 0f movl (%rdi), %ecx
> 6ee: 39 ce cmpl %ecx, %esi
> 6f0: 74 0e je 0x700 <.text+0x30>
> 6f2: 8b 37 movl (%rdi), %esi
> 6f4: 85 f6 testl %esi, %esi
> 6f6: 75 e1 jne 0x6d9 <.text+0x9>
> 6f8: 48 c7 c0 ff ff ff ff movq $-0x1, %rax
> 6ff: c3 retq
> $ mkdir -p /tmp/debug/.build-id/cf/
> $ ln -s /lib/modules/6.9.2-local/build/arch/x86/entry/vdso/vdso64.so.dbg /tmp/debug/.build-id/cf/702469f4637840fd6ba1a8d8a628ff83253d04.debug
> $ llvm-objdump-18 --debug-file-directory /tmp/debug -dS ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso | head -20
>
> ~/.debug/[vdso]/cf702469f4637840fd6ba1a8d8a628ff83253d04/vdso: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 00000000000006d0 <vread_hvclock>:
> ; hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
> 6d0: 48 8d 3d 29 d9 ff ff leaq -0x26d7(%rip), %rdi # 0xffffffffffffe000 <hvclock_page>
> 6d7: eb 19 jmp 0x6f2 <vread_hvclock+0x22>
> ; scale = READ_ONCE(tsc_pg->tsc_scale);
> 6d9: 4c 8b 0d 28 d9 ff ff movq -0x26d8(%rip), %r9 # 0xffffffffffffe008 <hvclock_page+0x8>
> ; offset = READ_ONCE(tsc_pg->tsc_offset);
> 6e0: 4c 8b 05 29 d9 ff ff movq -0x26d7(%rip), %r8 # 0xffffffffffffe010 <hvclock_page+0x10>
> ; asm volatile(ALTERNATIVE_2("rdtsc",
> 6e7: 0f 31 rdtsc
> 6e9: 90 nop
> 6ea: 90 nop
> 6eb: 90 nop
> ; } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
> 6ec: 8b 0f movl (%rdi), %ecx
> $
>
Yes, not only llvm-objdump. I can see other tools also can handle this and even
can download from online by Debuginfod.
- perf can search debugging info there if HAVE_DEBUGINFOD_SUPPORT.
- gdb can search debugging info there and download via Debuginfod if not exist.
While above requires debugging files are placed correctly in
/usr/lib/debug/.build-id/. For vdso mostly you need to copy it manully.
The target of this series is to handle it transparently, espacially for locally
built kernels.
>
>
--
Cheers,
Changbin Du
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