Re: [committed] Return to caller when _dl_fixup fails on hppa

[John David Anglin <dave.anglin@bell.net>]

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On 2017-07-17, at 7:11 AM, Carlos O'Donell wrote:

> On 07/17/2017 03:10 AM, Andreas Schwab wrote:
>> This information should be added in a comment.
> 
> Dave, Thanks for all the fixes. I agree with Andreas, this should be
> documented with a comment.

I committed the attached comment update.  I tied it to the BZ report so it's clear what we
are trying to fix.

At this time, Debian has a local patch which removes __gmon_start__ from crtn.S on hppa.

Dave
--
John David Anglin	dave.anglin@bell.net



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2017-07-23  John David Anglin  <danglin@gcc.gnu.org>

	[BZ 19170]
	* sysdeps/hppa/dl-trampoline.S (_dl_runtime_resolve): Revise comment.

diff --git a/sysdeps/hppa/dl-trampoline.S b/sysdeps/hppa/dl-trampoline.S
index f1294a931f..3165c6f0e2 100644
--- a/sysdeps/hppa/dl-trampoline.S
+++ b/sysdeps/hppa/dl-trampoline.S
@@ -82,9 +82,19 @@ _dl_runtime_resolve:
 	bl	_dl_fixup,%rp
 	copy	%r21,%r19		/* set fixup func ltp */
 
-	/* Sometimes a final executable may attempt to call an undefined
-	   weak function (e.g., __gmon_start__).  Return if the function
-	   was not resolved by _dl_fixup */
+	/* While the linker will set a function pointer to NULL when it
+	   encounters an undefined weak function, we need to dynamically
+	   detect removed weak functions.  The issue arises because a weak
+	   __gmon_start__ function was added to shared executables to work
+	   around issues in _init that are now resolved.  The presence of
+	   __gmon_start__ in every shared library breaks the linker
+	   `--as-needed' option.  This __gmon_start__ function does nothing
+	   but removal is tricky.  Depending on the binding, removal can
+	   cause an application using it to fault.  The call to _dl_fixup
+	   returns NULL when a function isn't resolved.  In order to help
+	   with __gmon_start__ removal, we return directly to the caller
+	   when _dl_fixup returns NULL.  This check could be removed when
+	   BZ 19170 is fixed.  */
 	comib,=	0,%r28,1f
 
 	/* Load up the returned func descriptor */