[PATCH] Fix PLT call stub for ppc64

[PATCH] Fix PLT call stub for ppc64

[Edjunior Barbosa Machado]

Hi,

GDB was unable to 'step' into a c/c++ function from a shared library on ppc64
due to a change in linker that removes a load
instruction from the PLT call stub
(http://sourceware.org/ml/binutils/2011-07/msg00141.html). This patch fixes this
on GDB, marking the mentioned instruction as optional, since it still might
appear if the linker is called with '--plt-static-chain'.

It also solves some unexpected failures in the testuite on ppc64 (verified on
fedora 17):

-FAIL: gdb.base/gdb1555.exp: Step into shared lib function
-FAIL: gdb.base/gdb1555.exp: Next while in a shared lib function
-FAIL: gdb.base/gnu-ifunc.exp: step
-FAIL: gdb.base/skip-solib.exp: step
-FAIL: gdb.base/skip-solib.exp: bt
-FAIL: gdb.base/so-impl-ld.exp: step into solib call
-FAIL: gdb.base/so-impl-ld.exp: step in solib call
-FAIL: gdb.base/so-impl-ld.exp: step out of solib call

Ok to commit?

Thanks,
--
Edjunior

gdb/ChangeLog
2012-11-07  Edjunior Machado  <emachado@linux.vnet.ibm.com>

	* ppc-linux-tdep.c (ppc64_standard_linkage3): Mark ld r11 instruction as
	optional, following the change in PLT call stub on linker.

---
 gdb/ppc-linux-tdep.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index ccded83..fcffa7d 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -446,8 +446,8 @@ static struct insn_pattern ppc64_standard_linkage3[] =
     /* mtctr r11 */
     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
 
-    /* ld r11, <any>(r2) */
-    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 0 },
+    /* ld r11, <any>(r2) <optional> */
+    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 1 },
       
     /* ld r2, <any>(r2) */
     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 2, 0, 0), 0 },
-- 
1.7.10.1

Re: [PATCH] Fix PLT call stub for ppc64

[Ulrich Weigand]

Edjunior Machado wrote:

> GDB was unable to 'step' into a c/c++ function from a shared library on ppc64
> due to a change in linker that removes a load
> instruction from the PLT call stub
> (http://sourceware.org/ml/binutils/2011-07/msg00141.html). This patch fixes this
> on GDB, marking the mentioned instruction as optional, since it still might
> appear if the linker is called with '--plt-static-chain'.

Hmm, looking at the binutils patch, it seems to me that the static chain load
in the *other* PLT stubs (ppc64_standard_linkage1, ppc64_standard_linkage2)
should now also be marked as optional, shouldn't it?

Otherwise looks good to me.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [PATCH] Fix PLT call stub for ppc64

[Edjunior Barbosa Machado]

On 11/07/2012 05:21 PM, Ulrich Weigand wrote:
> Hmm, looking at the binutils patch, it seems to me that the static chain load
> in the *other* PLT stubs (ppc64_standard_linkage1, ppc64_standard_linkage2)
> should now also be marked as optional, shouldn't it?
> 

Thanks a lot for the comment, Ulrich.
Here's the new version of the patch, updating the other PLT stubs patterns
accordingly.

-- 
Edjunior

gdb/ChangeLog
2012-11-07  Edjunior Machado  <emachado@linux.vnet.ibm.com>

	* ppc-linux-tdep.c: Mark ld r11 instructions as optional, following the
	change in PLT call stubs on linker.

---
 gdb/ppc-linux-tdep.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index ccded83..f88d697 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -390,8 +390,8 @@ static struct insn_pattern ppc64_standard_linkage1[] =
     /* mtctr r11 */
     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
 
-    /* ld r11, <any>(r12) */
-    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 0 },
+    /* ld r11, <any>(r12) <optional> */
+    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 1 },
       
     /* bctr */
     { -1, 0x4e800420, 0 },
@@ -421,8 +421,8 @@ static struct insn_pattern ppc64_standard_linkage2[] =
     /* ld r2, <any>(r12) */
     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 12, 0, 0), 0 },
 
-    /* ld r11, <any>(r12) */
-    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 0 },
+    /* ld r11, <any>(r12) <optional> */
+    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 1 },
       
     /* bctr */
     { -1, 0x4e800420, 0 },
@@ -446,8 +446,8 @@ static struct insn_pattern ppc64_standard_linkage3[] =
     /* mtctr r11 */
     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
 
-    /* ld r11, <any>(r2) */
-    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 0 },
+    /* ld r11, <any>(r2) <optional> */
+    { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 1 },
       
     /* ld r2, <any>(r2) */
     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 2, 0, 0), 0 },
-- 
1.7.10.1

Re: [PATCH] Fix PLT call stub for ppc64

[Ulrich Weigand]

Edjunior Machado wrote:

> gdb/ChangeLog
> 2012-11-07  Edjunior Machado  <emachado@linux.vnet.ibm.com>
> 
> 	* ppc-linux-tdep.c: Mark ld r11 instructions as optional, following the
> 	change in PLT call stubs on linker.

You should call out the modified variables (ppc64_standard_linkage1 etc)
in the ChangeLog.   Otherwise, this is OK.

Thanks,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com

Re: [PATCH] Fix PLT call stub for ppc64

[Edjunior Barbosa Machado]

On 11/08/2012 11:45 AM, Ulrich Weigand wrote:
> You should call out the modified variables (ppc64_standard_linkage1 etc)
> in the ChangeLog.   Otherwise, this is OK.
> 

Thanks again, Ulrich. Checked in with the suggested addition:

	* ppc-linux-tdep.c (ppc64_standard_linkage1, ppc64_standard_linkage2,
	ppc64_standard_linkage3): Mark ld r11 instructions as optional,
	following the change in PLT call stubs on linker.

http://sourceware.org/ml/gdb-cvs/2012-11/msg00054.html

Thanks,
-- 
Edjunior