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

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Dec 08, 2022 at 09:11:54AM -0500, Marek Polacek via Gcc-patches wrote:
> On Thu, Dec 08, 2022 at 08:25:26AM +0100, Florian Weimer wrote:
> > * Marek Polacek via Gcc-patches:
> > 
> > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > > index 726392409b6..2de14466dd3 100644
> > > --- a/gcc/doc/invoke.texi
> > > +++ b/gcc/doc/invoke.texi
> > > @@ -16510,6 +16510,14 @@ 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),
> > > +@option{-fno-optimize-sibling-calls} (which prevents optimizing sibling
> > > +and tail recursive calls), or @option{-fno-ipa-icf} (which disables Identical
> > > +Code Folding for functions and read-only variables).  Since multiple runs
> > > +of the program may yield backtraces with different addresses due to ASLR,
> > > +it may be desirable to turn off ASLR: @samp{setarch `uname -m` -R ./prog}.
> > 
> > What about -fasynchronous-unwind-tables?  It should help if ASAN ever
> > reports stray segmentation faults.  Whether it also helps in general
> > depends on whether ASAN maintains ABI around its instrumentation.
> 
> I'm not sure.  Someone else will have to decide if we want to mention
> that option as well.

-fasynchronous-unwind-tables is on by default on many targets, so I wouldn't
mention it:
grep asynchronous_unwind_tables common/*/*/* config/*/*
common/config/aarch64/aarch64-common.cc:    { OPT_LEVELS_ALL, OPT_fasynchronous_unwind_tables, NULL, 1 },
common/config/i386/i386-common.cc:  opts->x_flag_asynchronous_unwind_tables = 2;
common/config/loongarch/loongarch-common.cc:  { OPT_LEVELS_ALL, OPT_fasynchronous_unwind_tables, NULL, 1 },
common/config/rs6000/rs6000-common.cc:  opts->x_flag_asynchronous_unwind_tables = 1;
common/config/s390/s390-common.cc:  opts->x_flag_asynchronous_unwind_tables = 1;
config/i386/i386-options.cc:      if (opts->x_flag_asynchronous_unwind_tables == 2)
config/i386/i386-options.cc:	opts->x_flag_asynchronous_unwind_tables = !USE_IX86_FRAME_POINTER;
config/mips/mips.cc:      && !global_options_set.x_flag_asynchronous_unwind_tables)
config/mips/mips.cc:    flag_asynchronous_unwind_tables = 1;
config/rs6000/rs6000.cc:      && !OPTION_SET_P (flag_asynchronous_unwind_tables))
config/rs6000/rs6000.cc:    flag_asynchronous_unwind_tables = 1;

On the other side, the @samp{setarch `uname -m` -R ./prog} suggestion is
very Linux specific, so if we mention it at all, it should mention that
"e.g. on Linux through ..." or something similar.
I also wouldn't mention the "and read-only variables" part, that is
irrelevant for stack traces.

	Jakub