[PATCH v2 3/5] elf: Replace alloca with dl_scratch_buffer in _dl_load_cache_lookup

[H.J. Lu]

On Tue, May 19, 2026 at 1:26 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 15/05/26 19:00, H.J. Lu wrote:
> >> +
> >> +static int
> >> +do_test (void)
> >> +{
> >> +  /* Sanity: from the main thread (no stack pressure needed).  */
> >> +  dlopen_via_cache (NULL);
> >> +
> >> +  /* The motivating scenario: from a PTHREAD_STACK_MIN thread.  Before
> >> +     _dl_load_cache_lookup was converted to dl_scratch_buffer this would
> >> +     have alloca'd ~3 KB mid-dlopen and risked overflowing.  */
> >> +  size_t stacksize =
> >> +#ifdef PTHREAD_STACK_MIN
> >> +    PTHREAD_STACK_MIN;
> >> +#else
> >> +    support_small_thread_stack_size ();
> >
> > Shouldn't we use support_small_thread_stack_size unconditionally?
> The main issue with support_small_thread_stack_size is it defines a quite large
> thread stack, which would require to add a 'slack' stack usage on each test
> to triggers the stack overflow on unpatched libc.
>
> Also, from the original commit (36ada9ee2cd3b686df6952446b92816584eacbb8) it
> is not clear what exactly does not work with PTHREAD_STACK_MIN. I guess that
> would be some features that add some under the hood allocation like
> pthread_cancel (through libgcc_s.so dlopen), but I think we should also check
> whether the support_small_thread_stack_size is really required for some tests.

How about updating support_small_thread_stack_size to use
PTHREAD_STACK_MIN if defined?  Like this?

-- 
H.J.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: p.diff
Type: text/x-patch
Size: 2546 bytes
Desc: not available
URL: <https://sourceware.org/pipermail/libc-alpha/attachments/20260519/77f8b95b/attachment.bin>