Re: [PATCH 14/14] perf annotate-data: Add stack canary type

[Ian Rogers <irogers@xxxxxxxxxx>]

On Tue, Feb 6, 2024 at 3:19 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Fri, Feb 2, 2024 at 7:21 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > On Fri, Feb 2, 2024 at 2:05 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> > >
> > > When the stack protector is enabled, compiler would generate code to
> > > check stack overflow with a special value called 'stack carary' at
> > > runtime.  On x86_64, GCC hard-codes the stack canary as %gs:40.
> > >
> > > While there's a definition of fixed_percpu_data in asm/processor.h,
> > > it seems that the header is not included everywhere and many places
> > > it cannot find the type info.  As it's in the well-known location (at
> > > %gs:40), let's add a pseudo stack canary type to handle it specially.
> >
> > I wonder if cases like this can be handled by debug info rather than
> > special cases in the tool. Special cases are fine too, but are
> > potentially less portable.
>
> Agreed, but I couldn't find anything special in DWARF.

The fs and gs selectors are commonly used for thread local storage, so
could something like DW_OP_form_tls_address be used?
https://dwarfstd.org/issues/110803.1.html

Thanks,
Ian

> Thanks,
> Namhyung