Re: [PATCH v2 5/5] Linux: Consolidate auxiliary vector parsing

[Florian Weimer <fweimer@redhat.com>]

* Szabolcs Nagy:

> this seems to use memset now on aarch64 before irelative
> relocs are resolved in static binaries.
>
> which causes infinite loops in the iplt (i've also seen
> segfaults in the build log).
>
> i wonder what is a clean fix...

I've reverted this for now.  I missed the “static” part before; I think
our build environment is not really set up for such redirects.  Maybe
the easiest/cleanest way for now is to use an explicit initialization
loop for !SHARED, plus -fno-tree-loop-distribute-patterns.

> char seen_auxval[AT_MINSIGSTKSZ+1] = {0};
> 
> would not trigger memset (on aarch64).
> 
> as a bonus with such an array we can distinguish auxv unset and auxv 0.

The current code does not need that because it writes the default
values first:

  auxv_values[AT_ENTRY] = (ElfW(Addr)) ENTRY_POINT;
  auxv_values[AT_PAGESZ] = EXEC_PAGESIZE;
  auxv_values[AT_FPUCW] = _FPU_DEFAULT;

On the reader side, we would need to write

  if (seen_auxval[AT_CLKTCK])
    GLRO(dl_clktck) = auxv_values[AT_CLKTCK];

and

  if (seen_auxval[AT_FPUCW])
    auxv_values[AT_FPUCW] = auxv_values[AT_FPUCW];
  else
    auxv_values[AT_FPUCW] = _FPU_DEFAULT;

, which does not look like an improvement to me (neither
maintenance-wise nor code-size-wise).

Thanks,
Florian