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[ARM] Cortex A8 workarounds for PLT tail calls
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: binutils at sourceware dot org
- Cc: patches at linaro dot org
- Date: Tue, 12 Apr 2011 09:34:49 +0100
- Subject: [ARM] Cortex A8 workarounds for PLT tail calls
The linker has some workarounds for a Cortex A8 branch erratum. If a
32-bit Thumb branch straddles a page boundary, and branches to somewhere
in the first of the two pages, the linker will redirect it to a stub in
a different page.
This was failing to work correctly for non-call branches to PLTs. The stub
is itself a Thumb branch, but it branched directly to the ARM PLT code,
rather than to the preceding Thumb entry point.
(Normal calls to PLTs work fine. We use a BLX to an ARM stub,
which should and does then branch to the main PLT entry.)
Tested on arm-linux-gnueabi, both on binutils and GCC. The b-plt and
bcc-plt tests failed before the patch but pass after it. The other two
already passed, but I've included them for completeness. OK to install?
Richard
bfd/
* elf32-arm.c (cortex_a8_erratum_scan): If the stub is a Thumb
branch to a PLT entry, redirect it to the PLT's Thumb entry point.
ld/testsuite/
* ld-arm/cortex-a8-fix-b-plt.s, ld-arm/cortex-a8-fix-b-plt.d,
ld-arm/cortex-a8-fix-bcc-plt.s, ld-arm/cortex-a8-fix-bcc-plt.d,
ld-arm/cortex-a8-fix-bl-plt.s, ld-arm/cortex-a8-fix-bl-plt.d,
ld-arm/cortex-a8-fix-blx-plt.s, ld-arm/cortex-a8-fix-blx-plt.d,
ld-arm/cortex-a8-fix-plt.ld: New tests.
* ld-arm/arm-elf.exp: Run them.
Index: bfd/elf32-arm.c
===================================================================
--- bfd/elf32-arm.c 2011-04-11 16:23:04.000000000 +0100
+++ bfd/elf32-arm.c 2011-04-12 09:22:06.000000000 +0100
@@ -4556,6 +4556,7 @@ cortex_a8_erratum_scan (bfd *input_bfd,
bfd_vma target;
enum elf32_arm_stub_type stub_type = arm_stub_none;
struct a8_erratum_reloc key, *found;
+ bfd_boolean use_plt = FALSE;
key.from = base_vma + i;
found = (struct a8_erratum_reloc *)
@@ -4567,7 +4568,6 @@ cortex_a8_erratum_scan (bfd *input_bfd,
{
char *error_message = NULL;
struct elf_link_hash_entry *entry;
- bfd_boolean use_plt = FALSE;
/* We don't care about the error returned from this
function, only if there is glue or not. */
@@ -4671,6 +4671,12 @@ cortex_a8_erratum_scan (bfd *input_bfd,
offset =
(bfd_signed_vma) (found->destination - pc_for_insn);
+ /* If the stub will use a Thumb-mode branch to a
+ PLT target, redirect it to the preceding Thumb
+ entry point. */
+ if (stub_type != arm_stub_a8_veneer_blx && use_plt)
+ offset -= PLT_THUMB_STUB_SIZE;
+
target = pc_for_insn + offset;
/* The BLX stub is ARM-mode code. Adjust the offset to
Index: ld/testsuite/ld-arm/cortex-a8-fix-b-plt.s
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-b-plt.s 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,10 @@
+ .syntax unified
+ .globl foo
+ .type foo,%function
+ .thumb_func
+foo:
+ nop @ 0x00
+ movw r0,#0 @ 0x02
+ movw r0,#0 @ 0x06
+ movw r0,#0 @ 0x0a
+ b.w bar(PLT) @ 0x0e
Index: ld/testsuite/ld-arm/cortex-a8-fix-b-plt.d
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-b-plt.d 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,30 @@
+
+.*
+
+
+Disassembly of section \.plt:
+
+00008000 <\.plt>:
+ 8000: e52de004 push {lr} ; \(str lr, \[sp, #-4\]!\)
+ 8004: e59fe004 ldr lr, \[pc, #4\] ; 8010 <foo-0xfe0>
+ 8008: e08fe00e add lr, pc, lr
+ 800c: e5bef008 ldr pc, \[lr, #8\]!
+ 8010: 00000ffc \.word 0x00000ffc
+ 8014: 4778 bx pc
+ 8016: 46c0 nop ; \(mov r8, r8\)
+ 8018: e28fc600 add ip, pc, #0
+ 801c: e28cca00 add ip, ip, #0
+ 8020: e5bcfff8 ldr pc, \[ip, #4088\]! ; 0xff8
+
+Disassembly of section \.text:
+
+00008ff0 <foo>:
+ 8ff0: 46c0 nop ; \(mov r8, r8\)
+ 8ff2: f240 0000 movw r0, #0
+ 8ff6: f240 0000 movw r0, #0
+ 8ffa: f240 0000 movw r0, #0
+ 8ffe: f000 b803 b\.w 9008 <foo\+0x18>
+ 9002: 0000 movs r0, r0
+ 9004: 0000 movs r0, r0
+ 9006: 0000 movs r0, r0
+ 9008: f7ff b804 b\.w 8014 <foo-0xfdc>
Index: ld/testsuite/ld-arm/cortex-a8-fix-bcc-plt.s
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-bcc-plt.s 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,10 @@
+ .syntax unified
+ .globl foo
+ .type foo,%function
+ .thumb_func
+foo:
+ nop @ 0x00
+ movw r0,#0 @ 0x02
+ movw r0,#0 @ 0x06
+ movw r0,#0 @ 0x0a
+ beq.w bar(PLT) @ 0x0e
Index: ld/testsuite/ld-arm/cortex-a8-fix-bcc-plt.d
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-bcc-plt.d 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,32 @@
+
+.*
+
+
+Disassembly of section \.plt:
+
+00008000 <\.plt>:
+ 8000: e52de004 push {lr} ; \(str lr, \[sp, #-4\]!\)
+ 8004: e59fe004 ldr lr, \[pc, #4\] ; 8010 <foo-0xfe0>
+ 8008: e08fe00e add lr, pc, lr
+ 800c: e5bef008 ldr pc, \[lr, #8\]!
+ 8010: 00001004 \.word 0x00001004
+ 8014: 4778 bx pc
+ 8016: 46c0 nop ; \(mov r8, r8\)
+ 8018: e28fc600 add ip, pc, #0
+ 801c: e28cca01 add ip, ip, #4096 ; 0x1000
+ 8020: e5bcf000 ldr pc, \[ip\]!
+
+Disassembly of section \.text:
+
+00008ff0 <foo>:
+ 8ff0: 46c0 nop ; \(mov r8, r8\)
+ 8ff2: f240 0000 movw r0, #0
+ 8ff6: f240 0000 movw r0, #0
+ 8ffa: f240 0000 movw r0, #0
+ 8ffe: f000 b803 b\.w 9008 <foo\+0x18>
+ 9002: 0000 movs r0, r0
+ 9004: 0000 movs r0, r0
+ 9006: 0000 movs r0, r0
+ 9008: d001 beq\.n 900e <foo\+0x1e>
+ 900a: f7ff bffa b\.w 9002 <foo\+0x12>
+ 900e: f7ff b801 b\.w 8014 <foo-0xfdc>
Index: ld/testsuite/ld-arm/cortex-a8-fix-bl-plt.s
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-bl-plt.s 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,10 @@
+ .syntax unified
+ .globl foo
+ .type foo,%function
+ .thumb_func
+foo:
+ nop @ 0x00
+ movw r0,#0 @ 0x02
+ movw r0,#0 @ 0x06
+ movw r0,#0 @ 0x0a
+ bl bar(PLT) @ 0x0e
Index: ld/testsuite/ld-arm/cortex-a8-fix-bl-plt.d
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-bl-plt.d 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,28 @@
+
+.*
+
+
+Disassembly of section \.plt:
+
+00008000 <\.plt>:
+ 8000: e52de004 push {lr} ; \(str lr, \[sp, #-4\]!\)
+ 8004: e59fe004 ldr lr, \[pc, #4\] ; 8010 <foo-0xfe0>
+ 8008: e08fe00e add lr, pc, lr
+ 800c: e5bef008 ldr pc, \[lr, #8\]!
+ 8010: 00000ffc \.word 0x00000ffc
+ 8014: e28fc600 add ip, pc, #0
+ 8018: e28cca00 add ip, ip, #0
+ 801c: e5bcfffc ldr pc, \[ip, #4092\]! ; 0xffc
+
+Disassembly of section \.text:
+
+00008ff0 <foo>:
+ 8ff0: 46c0 nop ; \(mov r8, r8\)
+ 8ff2: f240 0000 movw r0, #0
+ 8ff6: f240 0000 movw r0, #0
+ 8ffa: f240 0000 movw r0, #0
+ 8ffe: f000 e804 blx 9008 <foo\+0x18>
+ 9002: 0000 movs r0, r0
+ 9004: 0000 movs r0, r0
+ 9006: 0000 movs r0, r0
+ 9008: eafffc01 b 8014 <foo-0xfdc>
Index: ld/testsuite/ld-arm/cortex-a8-fix-blx-plt.s
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-blx-plt.s 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,10 @@
+ .syntax unified
+ .globl foo
+ .type foo,%function
+ .thumb_func
+foo:
+ nop @ 0x00
+ movw r0,#0 @ 0x02
+ movw r0,#0 @ 0x06
+ movw r0,#0 @ 0x0a
+ blx bar @ 0x0e
Index: ld/testsuite/ld-arm/cortex-a8-fix-blx-plt.d
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-blx-plt.d 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,28 @@
+
+.*
+
+
+Disassembly of section \.plt:
+
+00008000 <\.plt>:
+ 8000: e52de004 push {lr} ; \(str lr, \[sp, #-4\]!\)
+ 8004: e59fe004 ldr lr, \[pc, #4\] ; 8010 <foo-0xfe0>
+ 8008: e08fe00e add lr, pc, lr
+ 800c: e5bef008 ldr pc, \[lr, #8\]!
+ 8010: 00000ffc \.word 0x00000ffc
+ 8014: e28fc600 add ip, pc, #0
+ 8018: e28cca00 add ip, ip, #0
+ 801c: e5bcfffc ldr pc, \[ip, #4092\]! ; 0xffc
+
+Disassembly of section \.text:
+
+00008ff0 <foo>:
+ 8ff0: 46c0 nop ; \(mov r8, r8\)
+ 8ff2: f240 0000 movw r0, #0
+ 8ff6: f240 0000 movw r0, #0
+ 8ffa: f240 0000 movw r0, #0
+ 8ffe: f000 e804 blx 9008 <foo\+0x18>
+ 9002: 0000 movs r0, r0
+ 9004: 0000 movs r0, r0
+ 9006: 0000 movs r0, r0
+ 9008: eafffc01 b 8014 <foo-0xfdc>
Index: ld/testsuite/ld-arm/cortex-a8-fix-plt.ld
===================================================================
--- /dev/null 2011-03-23 08:42:11.268792848 +0000
+++ ld/testsuite/ld-arm/cortex-a8-fix-plt.ld 2011-04-11 16:23:18.000000000 +0100
@@ -0,0 +1,18 @@
+OUTPUT_ARCH(arm)
+ENTRY(_start)
+SECTIONS
+{
+ . = 0x07000;
+ .hash : { *(.hash) }
+ .gnu.hash : { *(.gnu.hash) }
+ .dynsym : { *(.dynsym) }
+ .dynstr : { *(.dynstr) }
+ .rel.dyn : { *(.rel.dyn) }
+ .rel.plt : { *(.rel.plt) }
+ . = 0x08000;
+ .plt : { *(.plt) }
+ . = 0x08ff0;
+ .text : { *(.text) }
+ . = 0x10000;
+ .dynamic : { *(.dynamic) }
+}
Index: ld/testsuite/ld-arm/arm-elf.exp
===================================================================
--- ld/testsuite/ld-arm/arm-elf.exp 2011-04-11 16:23:04.000000000 +0100
+++ ld/testsuite/ld-arm/arm-elf.exp 2011-04-11 16:23:18.000000000 +0100
@@ -210,18 +210,38 @@ set armelftests {
"-EL -Ttext=0x8f00 --fix-cortex-a8" "-EL" {cortex-a8-fix-b.s}
{{objdump -dr cortex-a8-fix-b.d}}
"cortex-a8-fix-b"}
+ {"Cortex-A8 erratum fix, b.w to PLT"
+ "-EL -Tcortex-a8-fix-plt.ld --fix-cortex-a8 -shared" "-EL"
+ {cortex-a8-fix-b-plt.s}
+ {{objdump -dr cortex-a8-fix-b-plt.d}}
+ "cortex-a8-fix-b-plt"}
{"Cortex-A8 erratum fix, bl.w"
"-EL -Ttext=0x8f00 --fix-cortex-a8" "-EL" {cortex-a8-fix-bl.s}
{{objdump -dr cortex-a8-fix-bl.d}}
"cortex-a8-fix-bl"}
+ {"Cortex-A8 erratum fix, bl.w to PLT"
+ "-EL -Tcortex-a8-fix-plt.ld --fix-cortex-a8 -shared" "-EL"
+ {cortex-a8-fix-bl-plt.s}
+ {{objdump -dr cortex-a8-fix-bl-plt.d}}
+ "cortex-a8-fix-bl-plt"}
{"Cortex-A8 erratum fix, bcc.w"
"-EL -Ttext=0x8f00 --fix-cortex-a8" "-EL" {cortex-a8-fix-bcc.s}
{{objdump -dr cortex-a8-fix-bcc.d}}
"cortex-a8-fix-bcc"}
+ {"Cortex-A8 erratum fix, bcc.w to PLT"
+ "-EL -Tcortex-a8-fix-plt.ld --fix-cortex-a8 -shared" "-EL"
+ {cortex-a8-fix-bcc-plt.s}
+ {{objdump -dr cortex-a8-fix-bcc-plt.d}}
+ "cortex-a8-fix-bcc-plt"}
{"Cortex-A8 erratum fix, blx.w"
"-EL -Ttext=0x8f00 --fix-cortex-a8" "-EL" {cortex-a8-fix-blx.s}
{{objdump -dr cortex-a8-fix-blx.d}}
"cortex-a8-fix-blx"}
+ {"Cortex-A8 erratum fix, blx.w to PLT"
+ "-EL -Tcortex-a8-fix-plt.ld --fix-cortex-a8 -shared" "-EL"
+ {cortex-a8-fix-blx-plt.s}
+ {{objdump -dr cortex-a8-fix-blx-plt.d}}
+ "cortex-a8-fix-blx-plt"}
{"Cortex-A8 erratum fix, relocate b.w to ARM"
"-EL -Ttext=0x8f00 --fix-cortex-a8" "-EL" {cortex-a8-arm-target.s cortex-a8-fix-b-rel.s}
{{objdump -dr cortex-a8-fix-b-rel-arm.d}}