Re: [PATCH v2 2/6] elf: Avoid unnecessary slowdown from profiling with audit (BZ#15533)

[Alexander Monakov via Libc-alpha <libc-alpha@sourceware.org>]

On Mon, 19 Jul 2021, Adhemerval Zanella via Libc-alpha wrote:

> The rtld-audit interfaces introduces a slowdown due to enabling profiling

"interface" (my original message had "using the audit interfaces introduces").

> instrumentation (as if LD_AUDIT implied LD_PROFILE).  However, instrumenting
> is only necessary if one of audit libraries provides PLT (la_plt{enter,exit}
> 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.
> 
> Co-authored-by: Alexander Monakov <amonakov@ispras.dot.ru>

Please use my correct email here and in the Cc list (it's ispras.ru, not
ispras.dot.ru).

> ---
>  NEWS                 |  4 ++++
>  elf/Makefile         |  6 +++++-
>  elf/dl-reloc.c       | 12 +++++++++++-
>  elf/rtld.c           |  8 +-------
>  elf/tst-audit18.c    | 39 +++++++++++++++++++++++++++++++++++++++
>  elf/tst-auditmod18.c | 24 ++++++++++++++++++++++++
>  include/link.h       |  2 ++
>  7 files changed, 86 insertions(+), 9 deletions(-)
>  create mode 100644 elf/tst-audit18.c
>  create mode 100644 elf/tst-auditmod18.c
> 
> diff --git a/NEWS b/NEWS
> index 13ffe627da..8fde312ec6 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -76,6 +76,10 @@ Major new features:
>    equal to a giver integer.  This function is a GNU extension, although
>    Solaris also provides a similar function.
>  
> +* The audit libraries will avoid unnecessary slowdown if it is not required

"required for" or "... by"?

> +  either PLT tracking or symbol binding profiling (enabled with LA_FLG_BINDFROM
> +  or LA_FLG_BINDTO from la_objopen() callback).

It seems the part about binding needs to be updated, because the commit message
and the patch itself does not change anything for binding hooks? My
understanding always was that no change is necessary w.r.t la_symbind
callbacks: the loader invokes them when doing symbol resolution, and presence
of PLT does not matter.

Alexander