Re: [PATCH v2] trace-cmd: open code execvp routine to avoid multiple execve syscalls

[Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>]

On Sat, Jan 14, 2023 at 11:58:41AM +1300, Paulo Miguel Almeida wrote:
> In tracecmd/trace-record.c:<run_cmd>, trace-cmd record -F <executable>
> is launched via the libc's execvp() routine. The way that execvp() routine
> works is by invoking execve syscall for every entry on the $PATH if
> command specified is neither absolute nor relative which can come across
> as a bit cryptic to untrained eyes.
> 
> - absolute path example:
> 
>         # trace-cmd record -p function_graph \
>                 -g __x64_sys_execve -O nofuncgraph-irqs \
>                 -n __cond_resched --max-graph-depth 1  \
>                 -F /usr/bin/echo "ftrace" > /dev/null
> 
>         # trace-cmd report
>         echo-172994 [000] 185539.798539: funcgraph_entry:      ! 803.376 us |  __x64_sys_execve();
> 
> - PATH-dependent path example:
> 
>         # trace-cmd record -p function_graph \
>                 -g __x64_sys_execve -O nofuncgraph-irqs \
>                 -n __cond_resched --max-graph-depth 1  \
>                 -F echo "ftrace" > /dev/null
> 
>         # trace-cmd report
>         echo-172656 [002] 185009.671586: funcgraph_entry:      ! 288.732 us |  __x64_sys_execve();
>         echo-172656 [002] 185009.671879: funcgraph_entry:      ! 158.337 us |  __x64_sys_execve();
>         echo-172656 [002] 185009.672042: funcgraph_entry:      ! 161.843 us |  __x64_sys_execve();
>         echo-172656 [002] 185009.672207: funcgraph_entry:      ! 157.656 us |  __x64_sys_execve();
>         echo-172656 [002] 185009.672369: funcgraph_entry:      ! 156.343 us |  __x64_sys_execve();
>         echo-172656 [002] 185009.672529: funcgraph_entry:      ! 863.629 us |  __x64_sys_execve();
> 
> Open code the libc's execvp routine into trace-cmd so ftrace will only
> start recording once the command is found when it needs to be found in
> PATH.
> 
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
> ---
> Changelog:
> 
> - v2: open code execvp routine into trace-cmd. (Req. Steve Rostedt)
> - v1: https://lore.kernel.org/linux-trace-devel/Y7dUo6woh9Y31cdl@mail.google.com/
> ---

Ignore this patch. I just realised that I didn't tweak the CUnit tests.
I will submit another patch shortly.

- Paulo A.