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[PATCH] Enable use of ARMv5t BLX for Thumb-mode calls via PLT
- From: Julian Brown <julian at codesourcery dot com>
- To: binutils at sources dot redhat dot com
- Cc: Julian Brown <julian at codesourcery dot com>
- Date: Mon, 11 Apr 2005 19:55:12 +0100
- Subject: [PATCH] Enable use of ARMv5t BLX for Thumb-mode calls via PLT
Hi,
This patch allows the ARMv5t Thumb BLX instruction to be used
(optionally) to call PLT entries, which should provide a slight speed
boost. A previous, SymbianOS-specific version of the patch was posted here:
http://sourceware.org/ml/binutils/2005-03/msg00433.html
With this patch, the option "--use-thumb-blx" can be passed to the
linker to enable the use of the BLX instruction when the target supports
it. The format of the PLT itself isn't changed by this patch: there is
still a Thumb stub before each ARM PLT entry, but it is now unused. The
ARM mode entry is called directly instead.
Additionally, an instruction-encoding bug is fixed from the previous
unapplied version of the patch, and an uninitialised value is now
initialised (fix_v4bx field in elf32_arm_link_hash_table_create, just
cosmetic I think).
Tested on arm-none-eabi and arm-none-symbianelf.
OK to apply?
ChangeLog:
bfd:
* bfd-in.h (bfd_elf32_arm_set_target_relocs): Update prototype.
* bfd-in2.h: Regenerate.
* elf32-arm.c (elf32_arm_link_hash_table): New field, 'use_thumb_blx'.
(elf32_arm_link_hash_table_create): Initialise fix_v4bx,
use_thumb_blx.
(bfd_elf32_arm_set_target_relocs): Handle use_thumb_blx.
(elf32_arm_final_link_relocate): Use Thumb BLX for R_ARM_THM_PC22
relocations if requested to.
(elf32_arm_symbian_link_hash_table_create): Enable use_thumb_blx by
default for SymbianOS.
ld:
* ld.texinfo: Document --use-thumb-blx.
* emultempl/armelf.em (use_thumb_blx): New variable.
(arm_elf_create_output_section_statements): Communicate value of
use_thumb_blx to bfd.
(PARSE_AND_LIST_PROLOGUE): Add OPTION_USE_THUMB_BLX.
(PARSE_AND_LIST_OPTIONS): Add --use-thumb-blx option.
(PARSE_AND_LIST_ARGS_CASES): Add OPTION_USE_THUMB_BLX case.
Index: bfd/bfd-in.h
===================================================================
RCS file: /cvs/src/src/bfd/bfd-in.h,v
retrieving revision 1.97
diff -c -p -r1.97 bfd-in.h
*** bfd/bfd-in.h 30 Mar 2005 17:19:27 -0000 1.97
--- bfd/bfd-in.h 11 Apr 2005 18:49:01 -0000
*************** extern bfd_boolean bfd_elf32_arm_process
*** 816,822 ****
(bfd *, struct bfd_link_info *, int);
void bfd_elf32_arm_set_target_relocs
! (struct bfd_link_info *, int, char *, int);
extern bfd_boolean bfd_elf32_arm_get_bfd_for_interworking
(bfd *, struct bfd_link_info *);
--- 816,822 ----
(bfd *, struct bfd_link_info *, int);
void bfd_elf32_arm_set_target_relocs
! (struct bfd_link_info *, int, char *, int, int);
extern bfd_boolean bfd_elf32_arm_get_bfd_for_interworking
(bfd *, struct bfd_link_info *);
Index: bfd/elf32-arm.c
===================================================================
RCS file: /cvs/src/src/bfd/elf32-arm.c,v
retrieving revision 1.31
diff -c -p -r1.31 elf32-arm.c
*** bfd/elf32-arm.c 8 Apr 2005 11:47:59 -0000 1.31
--- bfd/elf32-arm.c 11 Apr 2005 18:49:01 -0000
*************** struct elf32_arm_link_hash_table
*** 1324,1329 ****
--- 1324,1332 ----
/* Nonzero to fix BX instructions for ARMv4 targets. */
int fix_v4bx;
+ /* Nonzero if the Thumb BLX instruction is available for use. */
+ int use_thumb_blx;
+
/* The number of bytes in the initial entry in the PLT. */
bfd_size_type plt_header_size;
*************** elf32_arm_link_hash_table_create (bfd *a
*** 1559,1564 ****
--- 1562,1569 ----
ret->plt_header_size = 20;
ret->plt_entry_size = 12;
#endif
+ ret->fix_v4bx = 0;
+ ret->use_thumb_blx = 0;
ret->symbian_p = 0;
ret->use_rel = 1;
ret->sym_sec.abfd = NULL;
*************** void
*** 2125,2131 ****
bfd_elf32_arm_set_target_relocs (struct bfd_link_info *link_info,
int target1_is_rel,
char * target2_type,
! int fix_v4bx)
{
struct elf32_arm_link_hash_table *globals;
--- 2130,2137 ----
bfd_elf32_arm_set_target_relocs (struct bfd_link_info *link_info,
int target1_is_rel,
char * target2_type,
! int fix_v4bx,
! int use_thumb_blx)
{
struct elf32_arm_link_hash_table *globals;
*************** bfd_elf32_arm_set_target_relocs (struct
*** 2144,2149 ****
--- 2150,2156 ----
target2_type);
}
globals->fix_v4bx = fix_v4bx;
+ globals->use_thumb_blx = use_thumb_blx;
}
#endif
*************** elf32_arm_final_link_relocate (reloc_how
*** 2893,2898 ****
--- 2900,2906 ----
bfd_signed_vma reloc_signed_min = ~ reloc_signed_max;
bfd_vma check;
bfd_signed_vma signed_check;
+ bfd_boolean thumb_plt_call = FALSE;
/* Need to refetch the addend and squish the two 11 bit pieces
together. */
*************** elf32_arm_final_link_relocate (reloc_how
*** 2942,2949 ****
value = (splt->output_section->vma
+ splt->output_offset
+ h->plt.offset);
! /* Target the Thumb stub before the ARM PLT entry. */
! value -= 4;
*unresolved_reloc_p = FALSE;
}
--- 2950,2968 ----
value = (splt->output_section->vma
+ splt->output_offset
+ h->plt.offset);
! if (globals->use_thumb_blx)
! {
! /* If the Thumb BLX instruction is available, convert the
! BL to a BLX instruction to call the ARM-mode PLT entry. */
! if ((lower_insn & (0x3 << 11)) == 0x3 << 11)
! {
! lower_insn = (lower_insn & ~(0x3 << 11)) | 0x1 << 11;
! thumb_plt_call = TRUE;
! }
! }
! else
! /* Target the Thumb stub before the ARM PLT entry. */
! value -= PLT_THUMB_STUB_SIZE;
*unresolved_reloc_p = FALSE;
}
*************** elf32_arm_final_link_relocate (reloc_how
*** 2967,2974 ****
overflow = TRUE;
#ifndef OLD_ARM_ABI
! if (r_type == R_ARM_THM_XPC22
! && ((lower_insn & 0x1800) == 0x0800))
/* For a BLX instruction, make sure that the relocation is rounded up
to a word boundary. This follows the semantics of the instruction
which specifies that bit 1 of the target address will come from bit
--- 2986,2994 ----
overflow = TRUE;
#ifndef OLD_ARM_ABI
! if ((r_type == R_ARM_THM_XPC22
! && ((lower_insn & 0x1800) == 0x0800))
! || thumb_plt_call)
/* For a BLX instruction, make sure that the relocation is rounded up
to a word boundary. This follows the semantics of the instruction
which specifies that bit 1 of the target address will come from bit
*************** elf32_arm_symbian_link_hash_table_create
*** 6505,6510 ****
--- 6525,6532 ----
/* The PLT entries are each three instructions. */
htab->plt_entry_size = 4 * NUM_ELEM (elf32_arm_symbian_plt_entry);
htab->symbian_p = 1;
+ /* Symbian uses armv5t or above, so use_thumb_blx is always true. */
+ htab->use_thumb_blx = 1;
htab->root.is_relocatable_executable = 1;
}
return ret;
Index: ld/ld.texinfo
===================================================================
RCS file: /cvs/src/src/ld/ld.texinfo,v
retrieving revision 1.140
diff -c -p -r1.140 ld.texinfo
*** ld/ld.texinfo 1 Feb 2005 17:31:01 -0000 1.140
--- ld/ld.texinfo 11 Apr 2005 18:49:01 -0000
*************** linker, which causes v4t @code{BX rM} in
*** 5262,5267 ****
--- 5262,5276 ----
In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
relocations are ignored.
+ @cindex USE_THUMB_BLX
+ @kindex --use-thumb-blx
+ The @samp{--use-thumb-blx} switch enables calls via the PLT in Thumb
+ code to use the BLX instruction, as defined in ARMv5t and above. This
+ should lead to such calls executing slightly faster.
+
+ This option is enabled implicitly for SymbianOS, so there is no need to
+ specify it if you are using that target.
+
@ifclear GENERIC
@lowersections
@end ifclear
Index: ld/emultempl/armelf.em
===================================================================
RCS file: /cvs/src/src/ld/emultempl/armelf.em,v
retrieving revision 1.44
diff -c -p -r1.44 armelf.em
*** ld/emultempl/armelf.em 3 Mar 2005 11:52:04 -0000 1.44
--- ld/emultempl/armelf.em 11 Apr 2005 18:49:01 -0000
*************** static int byteswap_code = 0;
*** 32,37 ****
--- 32,38 ----
static int target1_is_rel = 0${TARGET1_IS_REL};
static char *target2_type = "${TARGET2_TYPE}";
static int fix_v4bx = 0;
+ static int use_thumb_blx = 0;
static void
gld${EMULATION_NAME}_before_parse (void)
*************** static void
*** 192,198 ****
arm_elf_create_output_section_statements (void)
{
bfd_elf32_arm_set_target_relocs (&link_info, target1_is_rel, target2_type,
! fix_v4bx);
}
EOF
--- 193,199 ----
arm_elf_create_output_section_statements (void)
{
bfd_elf32_arm_set_target_relocs (&link_info, target1_is_rel, target2_type,
! fix_v4bx, use_thumb_blx);
}
EOF
*************** PARSE_AND_LIST_PROLOGUE='
*** 207,212 ****
--- 208,214 ----
#define OPTION_TARGET1_ABS 304
#define OPTION_TARGET2 305
#define OPTION_FIX_V4BX 306
+ #define OPTION_USE_THUMB_BLX 307
'
PARSE_AND_LIST_SHORTOPTS=p
*************** PARSE_AND_LIST_LONGOPTS='
*** 219,224 ****
--- 221,227 ----
{ "target1-abs", no_argument, NULL, OPTION_TARGET1_ABS},
{ "target2", required_argument, NULL, OPTION_TARGET2},
{ "fix-v4bx", no_argument, NULL, OPTION_FIX_V4BX},
+ { "use-thumb-blx", no_argument, NULL, OPTION_USE_THUMB_BLX},
'
PARSE_AND_LIST_OPTIONS='
*************** PARSE_AND_LIST_OPTIONS='
*** 228,233 ****
--- 231,237 ----
fprintf (file, _(" --target1=abs Interpret R_ARM_TARGET1 as R_ARM_ABS32\n"));
fprintf (file, _(" --target2=<type> Specify definition of R_ARM_TARGET2\n"));
fprintf (file, _(" --fix-v4bx Rewrite BX rn as MOV pc, rn for ARMv4\n"));
+ fprintf (file, _(" --use-thumb-blx Enable use of Thumb BLX instruction\n"));
'
PARSE_AND_LIST_ARGS_CASES='
*************** PARSE_AND_LIST_ARGS_CASES='
*** 258,263 ****
--- 262,271 ----
case OPTION_FIX_V4BX:
fix_v4bx = 1;
break;
+
+ case OPTION_USE_THUMB_BLX:
+ use_thumb_blx = 1;
+ break;
'
# We have our own after_open and before_allocation functions, but they call