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[ELF][ARM] Fix regression of BL->BLX substitution after D73542

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D73542 made a typo (`rel.type == R_PLT_PC`; should be `rel.expr`) and introduced a regression:
BL->BLX substitution was disabled when the target symbol is preemptible
(expr is R_PLT_PC).

The two added bl instructions in arm-thumb-interwork-shared.s check that
we patch BL to BLX.

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1047531
This commit is contained in:
Fangrui Song 2020-02-05 13:50:33 -08:00
parent 4a3760d2ba
commit 5461fa2b1f
2 changed files with 34 additions and 29 deletions
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4
lld/ELF/Arch/ARM.cpp
View File

@ -409,7 +409,7 @@ void ARM::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
// not of type STT_FUNC then we must preserve the original instruction.
// PLT entries are always ARM state so we know we don't need to interwork.
bool isBlx = (read32le(loc) & 0xfe000000) == 0xfa000000;
bool interwork = rel.sym && rel.sym->isFunc() && rel.type != R_PLT_PC;
bool interwork = rel.sym && rel.sym->isFunc() && rel.expr != R_PLT_PC;
if (interwork ? val & 1 : isBlx) {
// The BLX encoding is 0xfa:H:imm24 where Val = imm24:H:'1'
checkInt(loc, val, 26, rel);
@ -454,7 +454,7 @@ void ARM::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
// not of type STT_FUNC then we must preserve the original instruction.
// PLT entries are always ARM state so we know we need to interwork.
bool isBlx = (read16le(loc + 2) & 0x1000) == 0;
bool interwork = (rel.sym && rel.sym->isFunc()) || rel.type == R_PLT_PC;
bool interwork = (rel.sym && rel.sym->isFunc()) || rel.expr == R_PLT_PC;
if (interwork ? (val & 1) == 0 : isBlx) {
// We are writing a BLX. Ensure BLX destination is 4-byte aligned. As
// the BLX instruction may only be two byte aligned. This must be done

59
lld/test/ELF/arm-thumb-interwork-shared.s
View File

@ -1,7 +1,7 @@
// REQUIRES: arm
// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=thumbv7a-none-linux-gnueabi %s -o %t
// RUN: ld.lld %t --shared -o %t.so
// RUN: llvm-objdump -d -triple=thumbv7a-none-linux-gnueabi %t.so | FileCheck %s
// RUN: llvm-objdump -d --no-show-raw-insn -triple=thumbv7a-none-linux-gnueabi %t.so | FileCheck %s
.syntax unified
.global sym1
.global elsewhere
@ -10,46 +10,51 @@ sym1:
b.w elsewhere
b.w weakref
bl elsewhere
bl weakref
// Check that we generate a thunk for an undefined symbol called via a plt
// entry.
// CHECK: Disassembly of section .text:
// CHECK-EMPTY:
// CHECK-NEXT: sym1:
// CHECK-NEXT: 11e0: 00 f0 02 b8 b.w #4 <__ThumbV7PILongThunk_elsewhere>
// CHECK-NEXT: 11e4: 00 f0 06 b8 b.w #12 <__ThumbV7PILongThunk_weakref>
// CHECK-NEXT: 11e0: b.w #12 <__ThumbV7PILongThunk_elsewhere>
// CHECK-NEXT: b.w #20 <__ThumbV7PILongThunk_weakref>
// CHECK-NEXT: blx #68
// CHECK-NEXT: blx #80
// CHECK: __ThumbV7PILongThunk_elsewhere:
// CHECK-NEXT: 11e8: 40 f2 2c 0c movw r12, #44
// CHECK-NEXT: 11ec: c0 f2 00 0c movt r12, #0
// CHECK-NEXT: 11f0: fc 44 add r12, pc
// CHECK-NEXT: 11f2: 60 47 bx r12
// CHECK-NEXT: 11f0: movw r12, #52
// CHECK-NEXT: movt r12, #0
// CHECK-NEXT: add r12, pc
// CHECK-NEXT: bx r12
// CHECK: __ThumbV7PILongThunk_weakref:
// CHECK-NEXT: 11f4: 40 f2 30 0c movw r12, #48
// CHECK-NEXT: 11f8: c0 f2 00 0c movt r12, #0
// CHECK-NEXT: 11fc: fc 44 add r12, pc
// CHECK-NEXT: 11fe: 60 47 bx r12
// CHECK-NEXT: 11fc: movw r12, #56
// CHECK-NEXT: movt r12, #0
// CHECK-NEXT: add r12, pc
// CHECK-NEXT: bx r12
// CHECK: Disassembly of section .plt:
// CHECK-EMPTY:
// CHECK-NEXT: $a:
// CHECK-NEXT: 1200: 04 e0 2d e5 str lr, [sp, #-4]!
// CHECK-NEXT: 1204: 00 e6 8f e2 add lr, pc, #0, #12
// CHECK-NEXT: 1208: 02 ea 8e e2 add lr, lr, #8192
// CHECK-NEXT: 120c: 94 f0 be e5 ldr pc, [lr, #148]!
// CHECK-NEXT: 1210: str lr, [sp, #-4]!
// CHECK-NEXT: add lr, pc, #0, #12
// CHECK-NEXT: add lr, lr, #8192
// CHECK-NEXT: ldr pc, [lr, #148]!
// CHECK: $d:
// CHECK-NEXT: 1210: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 1214: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 1218: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 121c: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 1220: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: .word 0xd4d4d4d4
// CHECK-NEXT: .word 0xd4d4d4d4
// CHECK-NEXT: .word 0xd4d4d4d4
// CHECK: $a:
// CHECK-NEXT: 1220: 00 c6 8f e2 add r12, pc, #0, #12
// CHECK-NEXT: 1224: 02 ca 8c e2 add r12, r12, #8192
// CHECK-NEXT: 1228: 7c f0 bc e5 ldr pc, [r12, #124]!
// CHECK-NEXT: 1230: add r12, pc, #0, #12
// CHECK-NEXT: add r12, r12, #8192
// CHECK-NEXT: ldr pc, [r12, #124]!
// CHECK: $d:
// CHECK-NEXT: 122c: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 123c: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK: $a:
// CHECK-NEXT: 1230: 00 c6 8f e2 add r12, pc, #0, #12
// CHECK-NEXT: 1234: 02 ca 8c e2 add r12, r12, #8192
// CHECK-NEXT: 1238: 70 f0 bc e5 ldr pc, [r12, #112]!
// CHECK-NEXT: 1240: add r12, pc, #0, #12
// CHECK-NEXT: add r12, r12, #8192
// CHECK-NEXT: ldr pc, [r12, #112]!
// CHECK: $d:
// CHECK-NEXT: 123c: d4 d4 d4 d4 .word 0xd4d4d4d4
// CHECK-NEXT: 124c: d4 d4 d4 d4 .word 0xd4d4d4d4