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[ARM] Replace branches to undefined weak functions with NOP
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According to the code model (ARM, Thumb, Thumb2) this patch updates the b/bl/blx 0 instructions with NOP.
test/elf/ARM/weak-branch.test has been added with tests for all available NOP (A1, T1, T2 encodings).

Differential Revision: http://reviews.llvm.org/D8807

llvm-svn: 235498
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Leny Kholodov committed Apr 22, 2015
1 parent 0d49cf2 commit 9e4292c
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Showing 2 changed files with 261 additions and 0 deletions.
39 changes: 39 additions & 0 deletions lld/lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.cpp
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Expand Up @@ -510,6 +510,32 @@ static void relocR_ARM_LDR_PC_G2(uint8_t *location, uint64_t P, uint64_t S,
applyArmReloc(location, (uint32_t)result & mask, mask);
}

/// \brief Fixup unresolved weak reference with NOP instruction
static bool fixupUnresolvedWeakCall(uint8_t *location,
Reference::KindValue kindValue) {
//TODO: workaround for archs without NOP instruction
switch (kindValue) {
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
// Thumb32 NOP.W
write32le(location, 0x8000F3AF);
break;
case R_ARM_THM_JUMP11:
// Thumb16 NOP
write16le(location, 0xBF00);
break;
case R_ARM_CALL:
case R_ARM_JUMP24:
// A1 NOP<c>, save condition bits
applyArmReloc(location, 0x320F000, 0xFFFFFFF);
break;
default:
return false;
}

return true;
}

std::error_code ARMTargetRelocationHandler::applyRelocation(
ELFWriter &writer, llvm::FileOutputBuffer &buf, const AtomLayout &atom,
const Reference &ref) const {
Expand All @@ -522,6 +548,19 @@ std::error_code ARMTargetRelocationHandler::applyRelocation(
return std::error_code();
assert(ref.kindArch() == Reference::KindArch::ARM);

// Fixup unresolved weak references
if (!target) {
bool isCallFixed = fixupUnresolvedWeakCall(loc, ref.kindValue());

if (isCallFixed) {
DEBUG(llvm::dbgs() << "\t\tFixup unresolved weak reference '";
llvm::dbgs() << ref.target()->name() << "'";
llvm::dbgs() << " at address: 0x" << Twine::utohexstr(reloc);
llvm::dbgs() << (isCallFixed ? "\n" : " isn't possible\n"));
return std::error_code();
}
}

// Calculate proper initial addend for the relocation
const Reference::Addend addend =
readAddend(loc, ref.kindValue()) + ref.addend();
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222 changes: 222 additions & 0 deletions lld/test/elf/ARM/weak-branch.test
View file
@@ -0,0 +1,222 @@
# Check weak references fixup.

# RUN: yaml2obj -format=elf -docnum 1 %s > %t-jmp11.o
# RUN: lld -flavor gnu -target arm -m armelf_linux_eabi -Bstatic \
# RUN: --noinhibit-exec %t-jmp11.o -o %t
# RUN: llvm-objdump -s -t %t | FileCheck -check-prefix=JMP11-CHECK %s

# JMP11-CHECK: Contents of section .text:
# JMP11-CHECK: 400194 704700bf 01216be7 012100bf 002167e7
# ^ NOP (thumb16)
# 40019c: 2101 movs r1, #1
# 40019e: bf00 nop
# JMP11-CHECK: 4001a4 002100bf
# ^ NOP (thumb16)
# 4001a4: 2100 movs r1, #0
# 4001a6: bf00 nop
# JMP11-CHECK: SYMBOL TABLE:
# JMP11-CHECK: 00000000 w *UND* 00000000 __gnu_h2f_internal

# RUN: yaml2obj -format=elf -docnum 2 %s > %t-thm-call.o
# RUN: lld -flavor gnu -target arm -m armelf_linux_eabi -Bstatic \
# RUN: --noinhibit-exec %t-thm-call.o -o %t
# RUN: llvm-objdump -s -t %t | FileCheck -check-prefix=THM-CALL-CHECK %s

# THM-CALL-CHECK: Contents of section .text:
# THM-CALL-CHECK: 400064 80b500af fff7f4ff aff30080 03461846
# ^ NOP.W
# 400068: f7ff fff4 bl 400054 <my_fn>
# 40006c: f3af 8000 nop.w
# 400070: 4603 mov r3, r0 ; return value has not been changed after weak fn call
#
# THM-CALL-CHECK: SYMBOL TABLE:
# THM-CALL-CHECK: 00000000 w *UND* 00000000 weak_fn

# RUN: yaml2obj -format=elf -docnum 3 %s > %t-arm-call.o
# RUN: lld -flavor gnu -target arm -m armelf_linux_eabi -Bstatic \
# RUN: --noinhibit-exec %t-arm-call.o -o %t
# RUN: llvm-objdump -s -t %t | FileCheck -check-prefix=ARM-CALL-CHECK %s

# ARM-CALL-CHECK: Contents of section .text:
# ARM-CALL-CHECK: 400074 04b08de2 f5ffffeb 00f020e3 0030a0e1
# ^ NOP
# 400078: ebfffff5 bl 400054 <my_fn>
# 40007c: e320f000 nop {0}
# 400080: e1a03000 mov r3, r0 ; return value has not been changed after weak fn call
#
# ARM-CALL-CHECK: SYMBOL TABLE:
# ARM-CALL-CHECK: 00000000 w *UND* 00000000 weak_fn

# jump11.o
---
FileHeader:
Class: ELFCLASS32
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_ARM
Flags: [ EF_ARM_EABI_VER5 ]
Sections:
- Name: .text
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
AddressAlign: 0x0000000000000004
Content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
- Name: .rel.text
Type: SHT_REL
Link: .symtab
AddressAlign: 0x0000000000000004
Info: .text
Relocations:
- Offset: 0x000000000000012A
Symbol: __gnu_h2f_internal
Type: R_ARM_THM_JUMP11
- Offset: 0x0000000000000132
Symbol: __gnu_h2f_internal
Type: R_ARM_THM_JUMP11
- Name: .data
Type: SHT_PROGBITS
Flags: [ SHF_WRITE, SHF_ALLOC ]
AddressAlign: 0x0000000000000001
Content: ''
- Name: .bss
Type: SHT_NOBITS
Flags: [ SHF_WRITE, SHF_ALLOC ]
AddressAlign: 0x0000000000000001
Content: ''
Symbols:
Local:
- Name: .text
Type: STT_SECTION
Section: .text
- Name: .data
Type: STT_SECTION
Section: .data
- Name: .bss
Type: STT_SECTION
Section: .bss
- Name: '$t'
Section: .text
- Name: __gnu_f2h_internal
Type: STT_FUNC
Section: .text
Value: 0x0000000000000001
Size: 0x00000000000000C2
Global:
- Name: __gnu_f2h_ieee
Type: STT_FUNC
Section: .text
Value: 0x0000000000000125
Size: 0x0000000000000004
Visibility: STV_HIDDEN
- Name: __gnu_h2f_ieee
Type: STT_FUNC
Section: .text
Value: 0x0000000000000129
Size: 0x0000000000000004
Visibility: STV_HIDDEN
- Name: __gnu_f2h_alternative
Type: STT_FUNC
Section: .text
Value: 0x000000000000012D
Size: 0x0000000000000004
Visibility: STV_HIDDEN
- Name: __gnu_h2f_alternative
Type: STT_FUNC
Section: .text
Value: 0x0000000000000131
Size: 0x0000000000000004
Visibility: STV_HIDDEN
Weak:
- Name: __gnu_h2f_internal
# thm-call.o
---
FileHeader:
Class: ELFCLASS32
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_ARM
Flags: [ EF_ARM_EABI_VER5 ]
Sections:
- Name: .text
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
AddressAlign: 0x0000000000000004
Content: 80B400AF01231846BD465DF8047B704780B500AFFFF7FEFFFFF7FEFF0346184680BD00BF
- Name: .rel.text
Type: SHT_REL
Link: .symtab
AddressAlign: 0x0000000000000004
Info: .text
Relocations:
- Offset: 0x0000000000000014
Symbol: my_fn
Type: R_ARM_THM_CALL
- Offset: 0x0000000000000018
Symbol: weak_fn
Type: R_ARM_THM_CALL
Symbols:
Local:
- Name: .text
Type: STT_SECTION
Section: .text
- Name: '$t'
Section: .text
Global:
- Name: my_fn
Type: STT_FUNC
Section: .text
Value: 0x0000000000000001
Size: 0x0000000000000010
- Name: main
Type: STT_FUNC
Section: .text
Value: 0x0000000000000011
Size: 0x0000000000000012
Weak:
- Name: weak_fn
# arm-call.o
---
FileHeader:
Class: ELFCLASS32
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_ARM
Flags: [ EF_ARM_EABI_VER5 ]
Sections:
- Name: .text
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
AddressAlign: 0x0000000000000004
Content: 04B02DE500B08DE20130A0E30300A0E100D04BE204B09DE41EFF2FE100482DE904B08DE2FEFFFFEBFEFFFFEB0030A0E10300A0E10088BDE8
- Name: .rel.text
Type: SHT_REL
Link: .symtab
AddressAlign: 0x0000000000000004
Info: .text
Relocations:
- Offset: 0x0000000000000024
Symbol: my_fn
Type: R_ARM_CALL
- Offset: 0x0000000000000028
Symbol: weak_fn
Type: R_ARM_CALL
Symbols:
Local:
- Name: .text
Type: STT_SECTION
Section: .text
- Name: '$a'
Section: .text
Global:
- Name: my_fn
Type: STT_FUNC
Section: .text
Size: 0x000000000000001C
- Name: main
Type: STT_FUNC
Section: .text
Value: 0x000000000000001C
Size: 0x000000000000001C
Weak:
- Name: weak_fn
...

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