| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Fri, 28 Jun 2024 04:21:54 +0000
From: duchangbin <changbin.du@...wei.com>
To: Namhyung Kim <namhyung@...nel.org>, Adrian Hunter
<adrian.hunter@...el.com>
CC: Adrian Hunter <adrian.hunter@...el.com>, duchangbin
<changbin.du@...wei.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar
<mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...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>
Subject: Re: [PATCH v4 1/5] perf: support specify vdso path in cmdline
On Thu, Jun 27, 2024 at 04:53:18PM -0700, Namhyung Kim wrote:
> Hello guys,
>
> On Wed, Jun 26, 2024 at 01:32:42PM +0300, Adrian Hunter wrote:
> > On 26/06/24 05:26, duchangbin wrote:
> > > On Tue, Jun 25, 2024 at 04:20:49PM +0300, Adrian Hunter wrote:
> > >> On 25/06/24 06:37, 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.
> > >>
> > >> Would it be possible to add vdso and vdso debug to the build-id
> > >> cache and ensure perf can find it there?
> > >>
> > >> Typically, getting dsos from another machine is handled via
> > >> build-id cache e.g. what perf-archive does
> > >>
> > > Hmm. I agree this is better alternative approach for cross-machine analysis.
> > > When collecting vdsos to buildid cache, I think we can use the local searched
> > > objects (with debug symbols) instead if its build-id matches vdsos from process
> > > dumping (the real code ran).
> > >
> > > Currently I just follow what perf does for vmlinux so to reuse most of existing
> > > code. Maybe vmlinux is too big to add to buildid-cahce?
> > >
> > > Can we keep our current strategy for now? I'll think about above options when
> > > I have more time.
> > >
> >
> > I tried adding vdso via perf buildid-cache. It doesn't work only
> > because the lookup expects the basename to be "vdso" but it is
> > "elf".
> >
> > Adding a link from "vdso" to "elf" made it work e.g.
> >
> > $ cat gettimeofday-test.c
> > #include <stdio.h>
> > #include <sys/time.h>
> >
> > int main()
> > {
> > struct timeval tv;
> > int ret;
> >
> > ret = gettimeofday(&tv, NULL);
> > if (ret == -1) {
> > fprintf(stderr, "gettimeofday failed\n");
> > return 1;
> > }
> >
> > printf("%lu.%lu\n", (unsigned long)tv.tv_sec, (unsigned long)tv.tv_usec);
> >
> > return 0;
> > $ perf record -e intel_pt//u ./gettimeofday-test
> > 1719397042.892837
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.026 MB perf.data ]
> > $ perf script --itrace=e
> > $ perf buildid-cache --remove /lib/modules/6.5.0-41-generic/vdso/vdso64.so
> > $ perf script --itrace=e
> > Warning:
> > 2 instruction trace errors
> > instruction trace error type 1 time 525345.386424204 cpu 4 pid 198976 tid 198976 ip 0x7ffddb0e8e00 code 5: Failed to get instruction
> > instruction trace error type 1 time 525345.386424829 cpu 4 pid 198976 tid 198976 ip 0x7ffddb0e884d code 5: Failed to get instruction
> > $ perf buildid-cache --add /lib/modules/6.5.0-41-generic/vdso/vdso64.so
> > $ perf script --itrace=e
> > Warning:
> > 2 instruction trace errors
> > instruction trace error type 1 time 525345.386424204 cpu 4 pid 198976 tid 198976 ip 0x7ffddb0e8e00 code 5: Failed to get instruction
> > instruction trace error type 1 time 525345.386424829 cpu 4 pid 198976 tid 198976 ip 0x7ffddb0e884d code 5: Failed to get instruction
> > $ cd ~/.debug/.build-id/c3/530aed66e71bfd10af66039f58cc7c4d2eaba8
> > ~/.debug/.build-id/c3/530aed66e71bfd10af66039f58cc7c4d2eaba8$ ln -s elf vdso
> > ~/.debug/.build-id/c3/530aed66e71bfd10af66039f58cc7c4d2eaba8$ ls -l
> > total 36
> > -rw-r--r-- 1 ahunter ahunter 33272 Jun 26 13:17 elf
> > -rw-r----- 1 ahunter ahunter 0 Jun 26 13:17 probes
> > lrwxrwxrwx 1 ahunter ahunter 3 Jun 26 13:18 vdso -> elf
> > /.debug/.build-id/c3/530aed66e71bfd10af66039f58cc7c4d2eaba8$ cd
> > $ perf script --itrace=e
> > $
> >
> > So maybe a change could be made to build_id_cache__add() to add
> > the extra link if the file name matches vdso
>
> Thanks for doing this! I noticed buildid_cache__basename() will handle
> the name properly once it realizes the file is a vdso. Maybe we can
> check the filepath with some patterns, or simply add an command line
> option to say it's a vdso.
>
> Thanks,
> Namhyung
>
I added some tricks for vdso in build_id_cache__add(). It replace vdso object
with debugging one if found. Is this okay?
+static char *build_id_cache__find_debug_vdso(const char *sbuild_id)
+{
+ char sbuild_id_tmp[SBUILD_ID_SIZE];
+ struct build_id bid;
+ int i, ret = 0;
+
+ printf("Looking at the vdso_path (%d entries long)\n",
+ vdso_paths.nr_entries + 1);
+
+ for (i = 0; i < vdso_paths.nr_entries; ++i) {
+ ret = filename__read_build_id(vdso_paths.paths[i], &bid);
+ if (ret < 0)
+ continue;
+
+ build_id__sprintf(&bid, sbuild_id_tmp);
+ if (!strcmp(sbuild_id, sbuild_id_tmp)) {
+ printf("Found debugging vdso %s\n", vdso_paths.paths[i]);
+ return strdup(vdso_paths.paths[i]);
+ }
+ }
+
+ return NULL;
+}
+
int
build_id_cache__add(const char *sbuild_id, const char *name, const char *realname,
struct nsinfo *nsi, bool is_kallsyms, bool is_vdso,
const char *proper_name, const char *root_dir)
{
const size_t size = PATH_MAX;
- char *filename = NULL, *dir_name = NULL, *linkname = zalloc(size), *tmp;
+ char *filename = NULL, *dir_name = NULL, *vdso_name = NULL, *linkname = zalloc(size), *tmp;
char *debugfile = NULL;
int err = -1;
+ /* replace vdso object with debugging one if found */
+ if (is_vdso) {
+ vdso_name = build_id_cache__find_debug_vdso(sbuild_id);
+ if (vdso_name)
+ name = realname = vdso_name;
+ }
+
if (!proper_name)
proper_name = name;
>
--
Cheers,
Changbin Du
Powered by blists - more mailing lists