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Re: [BUG?] GCC 4.5.2 produces deprecated ARM relocation
- From: Matthew Gretton-Dann <matthew dot gretton-dann at arm dot com>
- To: Nick Clifton <nickc at redhat dot com>
- Cc: Richard Earnshaw <Richard dot Earnshaw at arm dot com>, Ben Gamari <bgamari dot foss at gmail dot com>, "binutils at sourceware dot org" <binutils at sourceware dot org>
- Date: Wed, 26 Oct 2011 17:10:17 +0100
- Subject: Re: [BUG?] GCC 4.5.2 produces deprecated ARM relocation
- References: <87lisglw3i.fsf@gmail.com> <4EA57E62.8020802@redhat.com> <4EA7D989.1010106@arm.com> <4EA7F90F.1040208@redhat.com>
Nick,
On 26/10/11 13:11, Nick Clifton wrote:
Hi Richard,
GCC is adding this suffix because the -fPIC flag enables NEED_PLT_RELOC
(see gcc/config/arm/elf.h). Why elf.h is doing this I am not sure -
backwards compatibility maybe ? Anyway it is GCC that needs fixing, not
GAS.
I disagree, gas should just ignore the suffix when generating EABI
conforming objects.
Well I based my conclusion upon this note in gas/doc/c-arm.texi:
For compatibility with older toolchains the assembler
also accepts @code{(PLT)} after branch targets. This
will generate the deprecated @samp{R_ARM_PLT32} relocation.
I do not mind enhancing the assembler however, so what do you think of
the attached patch ?
Some comments below.
Cheers
Nick
gas/ChangeLog
2011-10-26 Nick Clifton<nickc@redhat.com>
* config/tc-arm.c (md_begin): Remove ARM_PLT32 reloc associated
with the (PLT) instruction suffix when operating in eabi mode.
* doc/c-arm.texi (ARM_Relocations): Extend description of (PLT)
suffix.
arm.gas.plt32.patch
Index: gas/config/tc-arm.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-arm.c,v
retrieving revision 1.502
diff -u -3 -p -r1.502 tc-arm.c
--- gas/config/tc-arm.c 18 Oct 2011 14:41:53 -0000 1.502
+++ gas/config/tc-arm.c 26 Oct 2011 12:03:34 -0000
@@ -32,7 +32,7 @@
#include "safe-ctype.h"
#include "subsegs.h"
#include "obstack.h"
-
+#include "libiberty.h"
#include "opcode/arm.h"
#ifdef OBJ_ELF
@@ -22420,8 +22422,16 @@ md_begin (void)
hash_insert (arm_barrier_opt_hsh, barrier_opt_names[i].template_name,
(void *) (barrier_opt_names + i));
#ifdef OBJ_ELF
- for (i = 0; i< sizeof (reloc_names) / sizeof (struct reloc_entry); i++)
- hash_insert (arm_reloc_hsh, reloc_names[i].name, (void *) (reloc_names + i));
+ for (i = 0; i< ARRAY_SIZE (reloc_names); i++)
+ {
+ struct reloc_entry * entry = reloc_names + i;
+
+ if (arm_is_eabi()&& entry->reloc == BFD_RELOC_ARM_PLT32)
+ /* This makes encode_branch() use the EABI versions of this relocation. */
+ entry->reloc = BFD_RELOC_UNUSED;
+
+ hash_insert (arm_reloc_hsh, entry->name, (void *) entry);
+ }
While this is probably the simplest way to fix this in terms of code
change I wonder whether it would be better to actually modify the
encode_branch function?
By this I mean change the following:
> inst.reloc.type = inst.operands[0].imm == BFD_RELOC_ARM_PLT32
> ? BFD_RELOC_ARM_PLT32
> : thumb_mode ? BFD_RELOC_ARM_THM_TLS_CALL : BFD_RELOC_ARM_TLS_CALL;
so that when we are on an EABI target we set inst.reloc.type to
default_reloc.
This also then allows us to ensure that the BFD_RELOC_ARM_* value in
default_reloc really maps to R_ARM_CALL or R_ARM_JUMP24 as the
documentation says :-).
I'm also concerned at else will happen if we stop marking these
relocations as BFD_RELOC_ARM_PLT32. For instance in arm_fix_adjustable
there is code to not allow symbols to be discarded on GOT related relocs
which depends on this relocation type.
#endif
set_constant_flonums ();
Index: gas/doc/c-arm.texi
===================================================================
RCS file: /cvs/src/src/gas/doc/c-arm.texi,v
retrieving revision 1.85
diff -u -3 -p -r1.85 c-arm.texi
--- gas/doc/c-arm.texi 31 May 2011 14:12:54 -0000 1.85
+++ gas/doc/c-arm.texi 26 Oct 2011 12:03:34 -0000
@@ -493,8 +493,10 @@ and
@code{TPOFF}.
For compatibility with older toolchains the assembler also accepts
-@code{(PLT)} after branch targets. This will generate the deprecated
-@samp{R_ARM_PLT32} relocation.
+@code{(PLT)} after branch targets. On legacy targets this will
+generate the deprecated @samp{R_ARM_PLT32} relocation. On EABI
+targets it will encode either the @samp{R_ARM_CALL} or
+@samp{R_ARM_JUMP24} relocation, as appropriate.
@cindex MOVW and MOVT relocations, ARM
Relocations for @samp{MOVW} and @samp{MOVT} instructions can be generated
Index: gas/testsuite/gas/arm/pic.d
===================================================================
RCS file: /cvs/src/src/gas/testsuite/gas/arm/pic.d,v
retrieving revision 1.15
diff -u -3 -p -r1.15 pic.d
--- gas/testsuite/gas/arm/pic.d 7 Mar 2006 08:39:21 -0000 1.15
+++ gas/testsuite/gas/arm/pic.d 26 Oct 2011 12:03:34 -0000
@@ -13,7 +13,7 @@ Disassembly of section .text:
00+0<[^>]*> eb...... bl 00+.<[^>]*>
0: R_ARM_(PC24|CALL) foo.*
00+4<[^>]*> eb...... bl 0[0123456789abcdef]+<[^>]*>
- 4: R_ARM_PLT32 foo
+ 4: R_ARM_(PLT32|CALL) foo
\.\.\.
8: R_ARM_ABS32 sym
c: R_ARM_GOT32 sym
Thanks,
Matt
--
Matthew Gretton-Dann
Principal Engineer, PD Software - Tools, ARM Ltd