Re: [PATCH v2] docs: Suggest options to improve ASAN stack traces

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Dec 08, 2022 at 09:34:34AM -0500, Marek Polacek wrote:
> I got a complaint that while Clang docs suggest options that improve
> the quality of the backtraces ASAN prints (cf.
> <https://clang.llvm.org/docs/AddressSanitizer.html#usage>), our docs
> don't say anything to that effect.  This patch amends that with a new
> paragraph.  (It deliberately doesn't mention -fno-omit-frame-pointer.)
> 
> gcc/ChangeLog:
> 
> 	* doc/invoke.texi (-fsanitize=address): Suggest options to improve
> 	stack traces.
> ---
>  gcc/doc/invoke.texi | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 726392409b6..1641efecf18 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -16510,6 +16510,15 @@ The option cannot be combined with @option{-fsanitize=thread} or
>  @option{-fsanitize=hwaddress}.  Note that the only target
>  @option{-fsanitize=hwaddress} is currently supported on is AArch64.
>  
> +To get more accurate stack traces, it is possible to use options such as
> +@option{-O} (which, for instance, prevents most function inlining),

Still not sure about this part.  For one, I wonder if we shouldn't
recommend -O0, -O1 or -Og instead of just one of them, and I'm also not sure
how much function inlining is prevented with -O1.
always_inline functions are certainly inlined even at -O0 or -Og (at least
when called directly), -O1 adds
    { OPT_LEVELS_1_PLUS_NOT_DEBUG, OPT_finline_functions_called_once, NULL, 1 },
to that, -O2 adds
    { OPT_LEVELS_2_PLUS, OPT_findirect_inlining, NULL, 1 },
    { OPT_LEVELS_2_PLUS, OPT_finline_small_functions, NULL, 1 },
    { OPT_LEVELS_2_PLUS, OPT_fpartial_inlining, NULL, 1 },
    { OPT_LEVELS_2_PLUS, OPT_finline_functions, NULL, 1 },
and -O3 further bumps some parameters:
    { OPT_LEVELS_3_PLUS, OPT__param_max_inline_insns_auto_, NULL, 30 },
    { OPT_LEVELS_3_PLUS, OPT__param_early_inlining_insns_, NULL, 14 },
    { OPT_LEVELS_3_PLUS, OPT__param_inline_heuristics_hint_percent_, NULL, 600 },
    { OPT_LEVELS_3_PLUS, OPT__param_inline_min_speedup_, NULL, 15 },
    { OPT_LEVELS_3_PLUS, OPT__param_max_inline_insns_single_, NULL, 200 },

> +@option{-fno-optimize-sibling-calls} (which prevents optimizing sibling

-fno-optimize-sibling-calls is the default for -O0/-O1/-Og; dunno if we
want to reiterate it.

> +and tail recursive calls), or @option{-fno-ipa-icf} (which disables Identical
> +Code Folding for functions).  Since multiple runs of the program may yield
> +backtraces with different addresses due to ASLR (Address Space Layout
> +Randomization), it may be desirable to turn ASLR off.  On Linux, this can be
> +achieved with @samp{setarch `uname -m` -R ./prog}.
> +
>  @item -fsanitize=kernel-address
>  @opindex fsanitize=kernel-address
>  Enable AddressSanitizer for Linux kernel.

	Jakub