[lld] r313915 - [ELF] Fix edge condition in thunk offset calculation
Shoaib Meenai via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 21 14:04:42 PDT 2017
Author: smeenai
Date: Thu Sep 21 14:04:42 2017
New Revision: 313915
URL: http://llvm.org/viewvc/llvm-project?rev=313915&view=rev
Log:
[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
Added:
lld/trunk/test/ELF/arm-thunk-edgecase.s
Modified:
lld/trunk/ELF/Thunks.cpp
Modified: lld/trunk/ELF/Thunks.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Thunks.cpp?rev=313915&r1=313914&r2=313915&view=diff
==============================================================================
--- lld/trunk/ELF/Thunks.cpp (original)
+++ lld/trunk/ELF/Thunks.cpp Thu Sep 21 14:04:42 2017
@@ -160,16 +160,17 @@ bool ThumbV7ABSLongThunk::isCompatibleWi
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(
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) {
Added: lld/trunk/test/ELF/arm-thunk-edgecase.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/arm-thunk-edgecase.s?rev=313915&view=auto
==============================================================================
--- lld/trunk/test/ELF/arm-thunk-edgecase.s (added)
+++ lld/trunk/test/ELF/arm-thunk-edgecase.s Thu Sep 21 14:04:42 2017
@@ -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
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