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[committed] Return to caller when _dl_fixup fails on hppa

Message ID 3C95024E-2059-4D16-B135-EFB4A57D5591@bell.net
State New
Headers show

Commit Message

John David Anglin July 16, 2017, 5:50 p.m. UTC 
The attached change modifies _dl_runtime_resolve to return to its caller when _dl_fixup
fails.  This can occur on hppa when the caller attempts to call an undefined weak function.
The old code would fault when _dl_fixup fails.

The most problematic function in this regard is __gmon_start__.  Currently, it is linked into
every shared object.  This breaks the --as-needed ld option.

On Debian, we have an additional patch to treat __gmon_start__ as a true weak symbol.
I don't plan to apply this change as it becomes tricky to rebuild a distribution.  Rebuilding
a shared library removes __gmon_start__ and this may break a package using the library.
This isn't a problem after everything is rebuilt.

Dave
--
John David Anglin	dave.anglin@bell.net
2017-07-16  John David Anglin  <danglin@gcc.gnu.org>

	* sysdeps/hppa/dl-trampoline.S (_dl_runtime_resolve): Return to caller
	if _dl_fixup fails.

Comments

Andreas Schwab July 16, 2017, 6:52 p.m. UTC | #1 
On Jul 16 2017, John David Anglin <dave.anglin@bell.net> wrote:

> The most problematic function in this regard is __gmon_start__.

The caller needs to check for NULL before calling it.

Andreas.
John David Anglin July 16, 2017, 7:46 p.m. UTC | #2 
On 2017-07-16, at 2:52 PM, Andreas Schwab wrote:

> On Jul 16 2017, John David Anglin <dave.anglin@bell.net> wrote:
> 
>> The most problematic function in this regard is __gmon_start__.
> 
> The caller needs to check for NULL before calling it.


That's assumed.  However, it doesn't work on hppa.  The caller has access to a non NULL pointer
to a function descriptor.  In the typical case with deferred binding, the function pointer is not resolved
until _dl_fixup is called.

Dave
--
John David Anglin	dave.anglin@bell.net
Andreas Schwab July 16, 2017, 9:31 p.m. UTC | #3 
On Jul 16 2017, John David Anglin <dave.anglin@bell.net> wrote:

> That's assumed.  However, it doesn't work on hppa.  The caller has access to a non NULL pointer
> to a function descriptor.

It works well on ia64 and ppc64, why not on hppa?

Andreas.
John David Anglin July 16, 2017, 10:02 p.m. UTC | #4 
On 2017-07-16, at 5:31 PM, Andreas Schwab wrote:

>> That's assumed.  However, it doesn't work on hppa.  The caller has access to a non NULL pointer
>> to a function descriptor.
> 
> It works well on ia64 and ppc64, why not on hppa?

32-bit hppa doesn't have official procedure descriptors (OPDs).  Carlos at one time indicated that
he wanted to rework  binutils elf32-hppa.c to use OPDs but it never happened.  As a result, undefined
weak symbols are poorly supported.

It was a bad design and HP recognized it when they created the 64-bit hppa and ia64 runtimes.  The
32-bit hpux linker doesn't support undefined weak symbols at all.  We worked around it with one-only
support in gcc.

Anyway, one compare instruction checking the return of _dl_fixup doesn't affect performance much.
It could be removed if the problems with undefined weak functions are resolved.

Dave
--
John David Anglin	dave.anglin@bell.net
Andreas Schwab July 17, 2017, 7:10 a.m. UTC | #5 
This information should be added in a comment.

Andreas.
Carlos O'Donell July 17, 2017, 11:11 a.m. UTC | #6 
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.
John David Anglin July 17, 2017, 11:52 a.m. UTC | #7 
On 2017-07-17, at 7:11 AM, Carlos O'Donell wrote:

> Dave, Thanks for all the fixes. I agree with Andreas, this should be
> documented with a comment.

No problem.  Probably next weekend.

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

Patch

diff --git a/sysdeps/hppa/dl-trampoline.S b/sysdeps/hppa/dl-trampoline.S
index 856339bffe..f1294a931f 100644
--- a/sysdeps/hppa/dl-trampoline.S
+++ b/sysdeps/hppa/dl-trampoline.S
@@ -82,6 +82,11 @@  _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 */
+	comib,=	0,%r28,1f
+
 	/* Load up the returned func descriptor */
 	copy	%r28, %r22
 	copy	%r29, %r19
@@ -107,6 +112,13 @@  _dl_runtime_resolve:
 	/* Jump to new function, but return to previous function */
 	bv	%r0(%r22)
 	ldw	-20(%sp),%rp
+
+1:
+	/* Return to previous function */
+	ldw	-148(%sp),%rp
+	bv	%r0(%rp)
+	ldo	-128(%sp),%sp
+
         .EXIT
         .PROCEND
 	cfi_endproc