Re: [PATCH 1/1 perf-tools] perf machine: Initialize machine->env to address a segfault

[Michael Petlan <mpetlan@redhat.com>]

On Tue, 26 Nov 2024, Arnaldo Carvalho de Melo wrote:
> Its used from trace__run(), for the 'perf trace' live mode, i.e. its
> strace-like, non-perf.data file processing mode, the most common one.
> 
> The trace__run() function will set trace->host using machine__new_host()
> that is supposed to give a machine instance representing the running
> machine, and since we'll use perf_env__arch_strerrno() to get the right
> errno -> string table, we need to use machine->env, so initialize it in
> machine__new_host().
> 
> Before the patch:
> 
>   (gdb) run trace --errno-summary -a sleep 1
>   <SNIP>
>    Summary of events:
> 
>    gvfs-afc-volume (3187), 2 events, 0.0%
> 
>      syscall            calls  errors  total       min       avg       max       stddev
>                                        (msec)    (msec)    (msec)    (msec)        (%)
>      --------------- --------  ------ -------- --------- --------- ---------     ------
>      pselect6               1      0     0.000     0.000     0.000     0.000      0.00%
> 
>    GUsbEventThread (3519), 2 events, 0.0%
> 
>      syscall            calls  errors  total       min       avg       max       stddev
>                                        (msec)    (msec)    (msec)    (msec)        (%)
>      --------------- --------  ------ -------- --------- --------- ---------     ------
>      poll                   1      0     0.000     0.000     0.000     0.000      0.00%
>   <SNIP>
>   Program received signal SIGSEGV, Segmentation fault.
>   0x00000000005caba0 in perf_env__arch_strerrno (env=0x0, err=110) at util/env.c:478
>   478		if (env->arch_strerrno == NULL)
>   (gdb) bt
>   #0  0x00000000005caba0 in perf_env__arch_strerrno (env=0x0, err=110) at util/env.c:478
>   #1  0x00000000004b75d2 in thread__dump_stats (ttrace=0x14f58f0, trace=0x7fffffffa5b0, fp=0x7ffff6ff74e0 <_IO_2_1_stderr_>) at builtin-trace.c:4673
>   #2  0x00000000004b78bf in trace__fprintf_thread (fp=0x7ffff6ff74e0 <_IO_2_1_stderr_>, thread=0x10fa0b0, trace=0x7fffffffa5b0) at builtin-trace.c:4708
>   #3  0x00000000004b7ad9 in trace__fprintf_thread_summary (trace=0x7fffffffa5b0, fp=0x7ffff6ff74e0 <_IO_2_1_stderr_>) at builtin-trace.c:4747
>   #4  0x00000000004b656e in trace__run (trace=0x7fffffffa5b0, argc=2, argv=0x7fffffffde60) at builtin-trace.c:4456
>   #5  0x00000000004ba43e in cmd_trace (argc=2, argv=0x7fffffffde60) at builtin-trace.c:5487
>   #6  0x00000000004c0414 in run_builtin (p=0xec3068 <commands+648>, argc=5, argv=0x7fffffffde60) at perf.c:351
>   #7  0x00000000004c06bb in handle_internal_command (argc=5, argv=0x7fffffffde60) at perf.c:404
>   #8  0x00000000004c0814 in run_argv (argcp=0x7fffffffdc4c, argv=0x7fffffffdc40) at perf.c:448
>   #9  0x00000000004c0b5d in main (argc=5, argv=0x7fffffffde60) at perf.c:560
>   (gdb)
> 
> After:
> 
>   root@number:~# perf trace -a --errno-summary sleep 1
>   <SNIP>
>      pw-data-loop (2685), 1410 events, 16.0%
> 
>      syscall            calls  errors  total       min       avg       max       stddev
>                                        (msec)    (msec)    (msec)    (msec)        (%)
>      --------------- --------  ------ -------- --------- --------- ---------     ------
>      epoll_wait           188      0   983.428     0.000     5.231    15.595      8.68%
>      ioctl                 94      0     0.811     0.004     0.009     0.016      2.82%
>      read                 188      0     0.322     0.001     0.002     0.006      5.15%
>      write                141      0     0.280     0.001     0.002     0.018      8.39%
>      timerfd_settime       94      0     0.138     0.001     0.001     0.007      6.47%
> 
>    gnome-control-c (179406), 1848 events, 20.9%
> 
>      syscall            calls  errors  total       min       avg       max       stddev
>                                        (msec)    (msec)    (msec)    (msec)        (%)
>      --------------- --------  ------ -------- --------- --------- ---------     ------
>      poll                 222      0   959.577     0.000     4.322    21.414     11.40%
>      recvmsg              150      0     0.539     0.001     0.004     0.013      5.12%
>      write                300      0     0.442     0.001     0.001     0.007      3.29%
>      read                 150      0     0.183     0.001     0.001     0.009      5.53%
>      getpid               102      0     0.101     0.000     0.001     0.008      7.82%
> 
>   root@number:~#
> 
> Fixes: 54373b5d53c1f6aa ("perf env: Introduce perf_env__arch_strerrno()")
> Reported-by: Veronika Molnarova <vmolnaro@redhat.com>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: Ian Rogers <irogers@google.com>
> Cc: James Clark <james.clark@linaro.org>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Kan Liang <kan.liang@linux.intel.com>
> Cc: Michael Petlan <mpetlan@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Thanks for fixing the segfault!

Acked-by: Michael Petlan <mpetlan@redhat.com>
Tested-by: Michael Petlan <mpetlan@redhat.com>

> ---
>  tools/perf/util/machine.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 4f0ac998b0ccfd7a..27d5345d2b307a97 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -134,6 +134,8 @@ struct machine *machine__new_host(void)
>  
>  		if (machine__create_kernel_maps(machine) < 0)
>  			goto out_delete;
> +
> +		machine->env = &perf_env;
>  	}
>  
>  	return machine;
> -- 
> 2.47.0
> 
>