Re: [PATCH v7 09/16] elf: Avoid unnecessary slowdown from profiling with audit (BZ#15533)

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella:

> The rtld-audit interfaces introduces a slowdown due to enabling
> profiling instrumentation (as if LD_AUDIT implied LD_PROFILE).
> However, instrumenting is only necessary if one of audit libraries
> provides PLT callbacks (la_pltenter or la_pltexit symbols).  Otherwise,
> the slowdown can be avoided.
>
> The following patch adjusts the logic that enables profiling to iterate
> over all audit modules and check if any of those provides a PLT hook.
> To keep la_symbind to work even without PLT callbacks, _dl_fixup now
> calls the audit callback if the modules implements it.
>
> Co-authored-by: Alexander Monakov <amonakov@ispras.ru>
>
> Checked on x86_64-linux-gnu, i686-linux-gnu, and aarch64-linux-gnu.
> ---
>  NEWS                  |  3 ++
>  elf/Makefile          | 14 ++++++-
>  elf/dl-reloc.c        | 20 ++++++++-
>  elf/dl-runtime.c      | 31 ++++++++++++++
>  elf/rtld.c            |  8 +---
>  elf/tst-audit19a.c    | 38 +++++++++++++++++
>  elf/tst-audit19b.c    | 94 +++++++++++++++++++++++++++++++++++++++++++
>  elf/tst-audit19bmod.c | 23 +++++++++++
>  elf/tst-auditmod19a.c | 25 ++++++++++++
>  elf/tst-auditmod19b.c | 46 +++++++++++++++++++++
>  include/link.h        |  2 +
>  11 files changed, 294 insertions(+), 10 deletions(-)
>  create mode 100644 elf/tst-audit19a.c
>  create mode 100644 elf/tst-audit19b.c
>  create mode 100644 elf/tst-audit19bmod.c
>  create mode 100644 elf/tst-auditmod19a.c
>  create mode 100644 elf/tst-auditmod19b.c

I like the version with the l_reloc_result check much better.

> diff --git a/elf/tst-audit19b.c b/elf/tst-audit19b.c
> new file mode 100644
> index 0000000000..da015734f2
> --- /dev/null
> +++ b/elf/tst-audit19b.c
> @@ -0,0 +1,94 @@

> +  setenv ("LD_AUDIT", "tst-auditmod18b.so", 0);
> +  struct support_capture_subprocess result
> +    = support_capture_subprogram (spargv[0], spargv);
> +  support_capture_subprocess_check (&result, "tst-audit18b", 0, sc_allow_stderr);
> +
> +  bool find_symbind = false;
> +
> +  FILE *out = fmemopen (result.err.buffer, result.err.length, "r");
> +  TEST_VERIFY (out != NULL);
> +  char *buffer = NULL;
> +  size_t buffer_length = 0;
> +  while (xgetline (&buffer, &buffer_length, out))
> +    if (startswith (buffer, "la_symbind: tst_audit18bmod1_func") == 0)
> +      find_symbind = true;
> +
> +  TEST_COMPARE (find_symbind, true);
> +
> +  free (buffer);
> +  xfclose (out);

You could use strstr to find the "\nla_symbind: tst_audit18bmod1_func"
string (possibly after altering the output so that the \n is always
there).  But the version above works for me as well.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian