Re: [COMMITTED] Remove useless comment from sysdeps/sparc/sparc32/dl-machine.h

[Zack Weinberg <zackw at panix dot com>]

On Mon, May 22, 2017 at 3:47 PM, Siddhesh Poyarekar
<siddhesh@sourceware.org> wrote:
> -      /* XXX The following is wrong!  Dave Miller rejected to implement it
> -        correctly.  If this causes problems shoot *him*!  */

You got me curious, so I did some archaeology.  This comment was
introduced in 1999, and unfortunately Drepper seems to have been in
the habit of copying changes out of what I assume was a Cygnus Inc
internal CVS repository in large batches, so the commit message is
unhelpful, but the original patch to this file
(https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=sysdeps/sparc/sparc32/dl-machine.h;h=8750791fe0cf20f55250ad4c2147ebb992cadb93;hp=e6debe05ac511232cad7856be66298359f32e7b4;hb=63ae7b6309964400c6289d9030c7d336a33b304f;hpb=b4cbd37109d882aa052e7973684774eaa887071b)
was

--- a/sysdeps/sparc/sparc32/dl-machine.h
+++ b/sysdeps/sparc/sparc32/dl-machine.h
@@ -56,7 +56,9 @@ elf_machine_matches_host (Elf32_Half e_machine)
       weak_extern (_dl_hwcap_mask);

       hwcap = WEAKADDR(_dl_hwcap);
-      return hwcap && (*hwcap & _dl_hwcap_mask & HWCAP_SPARC_V9);
+      /* XXX The following is wrong!  Dave Miller rejected to implement it
+        correctly.  If this causes problems shoot *him*!  */
+      return hwcap == NULL || (*hwcap & _dl_hwcap_mask & HWCAP_SPARC_V9);
     }
   else
     return 0;

and, if I'm reading the ChangeLog correctly, the true author was Jakub
Jelinek, who I've cc:ed just on the offchance he remembers what was
going on.

Note that this changes the sense of the test from "the hwcap is
available AND the flag HWCAP_SPARC_V9 is set" to "the hwcap is NOT
available OR the flag HWCAP_SPARC_V9 is set".  I do not know for sure,
but what this smells like to me is there may have been a bunch of
SPARCv9 binaries that were generated before hwcaps were introduced, so
they stopped working when ld.so started paying attention to hwcaps, so
Miller wanted to relax the rules and Jelinek didn't like that.

What's in the file *now* appears to have reverted to the old logic
(and that happened in 2003), so if my nose is correct, then the
comment is indeed completely obsolete.

zw