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[ELF] Fix edge condition in thunk offset calculation 

For ARM thunks, the `movt` half of the relocation was using an incorrect
offset (it was off by 4 bytes). The original intent seems to have been
for the offset to have been relative to the current instruction, in
which case the difference of 4 makes sense. As the code stands, however,
the offset is always calculated relative to the start of the thunk
(`P`), and so the `movw` and `movt` halves should use the same offset.
This requires a very particular offset between the thunk and its target
to be triggered, and it results in the `movt` half of the relocation
being off-by-one.

The tests here use ARM-Thumb interworking thunks, since those are the
only ARM thunks currently implemented. I actually encountered this with
a range extension thunk (having Peter's patches cherry-picked locally),
but the underlying issue is identical.

Differential Revision: https://reviews.llvm.org/D38112

llvm-svn: 313915
This commit is contained in:
Shoaib Meenai 2017-09-21 21:04:42 +00:00
parent 1a28f2a002
commit 75d616b13f
2 changed files with 46 additions and 7 deletions
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16
lld/ELF/Thunks.cpp
View File

@ -160,16 +160,17 @@ bool ThumbV7ABSLongThunk::isCompatibleWith(uint32_t RelocType) const {
void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
const uint8_t Data[] = {
0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) +8)
0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P+4) +8)
0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) + 8)
0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P) + 8)
0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc
0x1c, 0xff, 0x2f, 0xe1, // bx r12
};
uint64_t S = getARMThunkDestVA(Destination);
uint64_t P = ThunkSym->getVA();
uint64_t Offset = S - P - 16;
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, S - P - 16);
Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, S - P - 12);
Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, Offset);
Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, Offset);
}
void ARMV7PILongThunk::addSymbols(ThunkSection &IS) {
@ -187,15 +188,16 @@ bool ARMV7PILongThunk::isCompatibleWith(uint32_t RelocType) const {
void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const {
const uint8_t Data[] = {
0x4f, 0xf6, 0xf4, 0x7c, // P: movw ip,:lower16:S - (P + (L1-P) + 4)
0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P+4) + 4)
0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P) + 4)
0xfc, 0x44, // L1: add r12, pc
0x60, 0x47, // bx r12
};
uint64_t S = getARMThunkDestVA(Destination);
uint64_t P = ThunkSym->getVA() & ~0x1;
uint64_t Offset = S - P - 12;
memcpy(Buf, Data, sizeof(Data));
Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, S - P - 12);
Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, S - P - 8);
Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, Offset);
Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, Offset);
}
void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) {

37
lld/test/ELF/arm-thunk-edgecase.s Normal file
View File

@ -0,0 +1,37 @@
// REQUIRES: arm
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
// RUN: echo "SECTIONS { \
// RUN: .text_armfunc 0x1000 : { *(.text_armfunc) } \
// RUN: .text_thumbfunc 0x11010 : { *(.text_thumbfunc) } \
// RUN: }" > %tarm_to_thumb.script
// RUN: echo "SECTIONS { \
// RUN: .text_thumbfunc 0x1000 : { *(.text_thumbfunc) } \
// RUN: .text_armfunc 0x1100c : { *(.text_armfunc) } \
// RUN: }" > %tthumb_to_arm.script
// RUN: ld.lld -shared -Bsymbolic -script %tarm_to_thumb.script %t.o -o %tarm_to_thumb.so
// RUN: ld.lld -shared -Bsymbolic -script %tthumb_to_arm.script %t.o -o %tthumb_to_arm.so
// RUN: llvm-objdump -triple=armv7a-none-linux-gnueabi -d %tarm_to_thumb.so | FileCheck -check-prefix=ARM-TO-THUMB %s
// RUN: llvm-objdump -triple=thumbv7a-none-linux-gnueabi -d %tthumb_to_arm.so | FileCheck -check-prefix=THUMB-TO-ARM %s
.syntax unified
.arm
.section .text_armfunc, "ax", %progbits
.globl armfunc
armfunc:
b thumbfunc
.thumb
.section .text_thumbfunc, "ax", %progbits
.globl thumbfunc
.thumb_func
thumbfunc:
b.w armfunc
// ARM-TO-THUMB: __ARMV7PILongThunk_thumbfunc:
// ARM-TO-THUMB-NEXT: 1004: fd cf 0f e3 movw r12, #65533
// ARM-TO-THUMB-NEXT: 1008: 00 c0 40 e3 movt r12, #0
// THUMB-TO-ARM: __ThumbV7PILongThunk_armfunc:
// THUMB-TO-ARM-NEXT: 1004: 4f f6 fc 7c movw r12, #65532
// THUMB-TO-ARM-NEXT: 1008: c0 f2 00 0c movt r12, #0