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[ELF] Don't crash on R_X86_64_GOTPCRELX for test/binop instructions
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While MC did not produce R_X86_64_GOTPCRELX for test/binop instructions
(movl/adcl/addl/andl/...) before the previous commit, this code path has been
exercised by -fno-integrated-as for GNU as since 2016: -no-pie relaxing
may incorrectly access loc[-3] and produce a corrupted instruction.

Simply handle test/binop R_X86_64_GOTPCRELX like R_X86_64_GOTPCREL.
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@MaskRay
MaskRay committed Oct 24, 2020
1 parent f04d92a commit 398b810
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Showing 2 changed files with 58 additions and 29 deletions.
7 changes: 4 additions & 3 deletions lld/ELF/Arch/X86_64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -746,11 +746,12 @@ RelExpr X86_64::adjustRelaxExpr(RelType type, const uint8_t *data,
if (op == 0xff && (modRm == 0x15 || modRm == 0x25))
return R_RELAX_GOT_PC;

// We don't support test/binop instructions without a REX prefix.
if (type == R_X86_64_GOTPCRELX)
return relExpr;

// Relaxation of test, adc, add, and, cmp, or, sbb, sub, xor.
// If PIC then no relaxation is available.
// We also don't relax test/binop instructions without REX byte,
// they are 32bit operations and not common to have.
assert(type == R_X86_64_REX_GOTPCRELX);
return config->isPic ? relExpr : R_RELAX_GOT_PC_NOPIC;
}

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80 changes: 54 additions & 26 deletions lld/test/ELF/x86-64-gotpc-relax-nopic.s
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Original file line number Diff line number Diff line change
@@ -1,30 +1,39 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -relax-relocations -triple=x86_64-unknown-linux %s -o %t.o
# RUN: ld.lld --hash-style=sysv %t.o -o %t1
# RUN: ld.lld %t.o -o %t1
# RUN: llvm-readobj --symbols -r %t1 | FileCheck --check-prefix=SYMRELOC %s
# RUN: llvm-objdump -d --no-show-raw-insn %t1 | FileCheck --check-prefix=DISASM %s
# RUN: llvm-objdump -d --no-show-raw-insn --print-imm-hex %t1 | FileCheck --check-prefix=DISASM %s

## There is no relocations.
# SYMRELOC: Relocations [
# SYMRELOC-NEXT: ]
# SYMRELOC: Symbols [
# SYMRELOC: Symbol {
# SYMRELOC: Name: bar
# SYMRELOC-NEXT: Value: 0x202197
# SYMRELOC-NEXT: Value: 0x203248

## 2105751 = 0x202197 (bar)
# DISASM: Disassembly of section .text:
# DISASM-EMPTY:
# DISASM-NEXT: <_start>:
# DISASM-NEXT: 201158: adcq $2105751, %rax
# DISASM-NEXT: addq $2105751, %rbx
# DISASM-NEXT: andq $2105751, %rcx
# DISASM-NEXT: cmpq $2105751, %rdx
# DISASM-NEXT: orq $2105751, %rdi
# DISASM-NEXT: sbbq $2105751, %rsi
# DISASM-NEXT: subq $2105751, %rbp
# DISASM-NEXT: xorq $2105751, %r8
# DISASM-NEXT: testq $2105751, %r15
# DISASM-NEXT: 2011c8: adcl {{.*}}(%rip), %eax # 202240
# DISASM-NEXT: addl {{.*}}(%rip), %ebx # 202240
# DISASM-NEXT: andl {{.*}}(%rip), %ecx # 202240
# DISASM-NEXT: cmpl {{.*}}(%rip), %edx # 202240
# DISASM-NEXT: orl {{.*}}(%rip), %edi # 202240
# DISASM-NEXT: sbbl {{.*}}(%rip), %esi # 202240
# DISASM-NEXT: subl {{.*}}(%rip), %ebp # 202240
# DISASM-NEXT: xorl {{.*}}(%rip), %r8d # 202240
# DISASM-NEXT: testl %r15d, {{.*}}(%rip) # 202240
# DISASM-NEXT: 201200: adcq $0x203248, %rax
# DISASM-NEXT: addq $0x203248, %rbx
# DISASM-NEXT: andq $0x203248, %rcx
# DISASM-NEXT: cmpq $0x203248, %rdx
# DISASM-NEXT: orq $0x203248, %rdi
# DISASM-NEXT: sbbq $0x203248, %rsi
# DISASM-NEXT: subq $0x203248, %rbp
# DISASM-NEXT: xorq $0x203248, %r8
# DISASM-NEXT: testq $0x203248, %r15

# RUN: ld.lld --hash-style=sysv -shared %t.o -o %t2
# RUN: llvm-readobj -S -r -d %t2 | FileCheck --check-prefix=SEC-PIC %s
Expand All @@ -37,8 +46,8 @@
# SEC-PIC-NEXT: SHF_ALLOC
# SEC-PIC-NEXT: SHF_WRITE
# SEC-PIC-NEXT: ]
# SEC-PIC-NEXT: Address: 0x2348
# SEC-PIC-NEXT: Offset: 0x348
# SEC-PIC-NEXT: Address: 0x2380
# SEC-PIC-NEXT: Offset: 0x380
# SEC-PIC-NEXT: Size: 8
# SEC-PIC-NEXT: Link:
# SEC-PIC-NEXT: Info:
Expand All @@ -48,25 +57,32 @@
# SEC-PIC: 0x000000006FFFFFF9 RELACOUNT 1
# SEC-PIC: Relocations [
# SEC-PIC-NEXT: Section ({{.*}}) .rela.dyn {
# SEC-PIC-NEXT: 0x2348 R_X86_64_RELATIVE - 0x3350
# SEC-PIC-NEXT: 0x2380 R_X86_64_RELATIVE - 0x3388
# SEC-PIC-NEXT: }
# SEC-PIC-NEXT: ]

## Check that there was no relaxation performed. All values refer to got entry.
## Ex: 0x1000 + 4249 + 7 = 0x20A0
## 0x102a + 4207 + 7 = 0x20A0
# DISASM-PIC: Disassembly of section .text:
# DISASM-PIC-EMPTY:
# DISASM-PIC-NEXT: <_start>:
# DISASM-PIC-NEXT: 1268: adcq 4313(%rip), %rax
# DISASM-PIC-NEXT: addq 4306(%rip), %rbx
# DISASM-PIC-NEXT: andq 4299(%rip), %rcx
# DISASM-PIC-NEXT: cmpq 4292(%rip), %rdx
# DISASM-PIC-NEXT: orq 4285(%rip), %rdi
# DISASM-PIC-NEXT: sbbq 4278(%rip), %rsi
# DISASM-PIC-NEXT: subq 4271(%rip), %rbp
# DISASM-PIC-NEXT: xorq 4264(%rip), %r8
# DISASM-PIC-NEXT: testq %r15, 4257(%rip)
# DISASM-PIC-NEXT: 1268: adcl {{.*}}(%rip), %eax # 2380
# DISASM-PIC-NEXT: addl {{.*}}(%rip), %ebx # 2380
# DISASM-PIC-NEXT: andl {{.*}}(%rip), %ecx # 2380
# DISASM-PIC-NEXT: cmpl {{.*}}(%rip), %edx # 2380
# DISASM-PIC-NEXT: orl {{.*}}(%rip), %edi # 2380
# DISASM-PIC-NEXT: sbbl {{.*}}(%rip), %esi # 2380
# DISASM-PIC-NEXT: subl {{.*}}(%rip), %ebp # 2380
# DISASM-PIC-NEXT: xorl {{.*}}(%rip), %r8d # 2380
# DISASM-PIC-NEXT: testl %r15d, {{.*}}(%rip) # 2380
# DISASM-PIC-NEXT: 12a0: adcq {{.*}}(%rip), %rax # 2380
# DISASM-PIC-NEXT: addq {{.*}}(%rip), %rbx # 2380
# DISASM-PIC-NEXT: andq {{.*}}(%rip), %rcx # 2380
# DISASM-PIC-NEXT: cmpq {{.*}}(%rip), %rdx # 2380
# DISASM-PIC-NEXT: orq {{.*}}(%rip), %rdi # 2380
# DISASM-PIC-NEXT: sbbq {{.*}}(%rip), %rsi # 2380
# DISASM-PIC-NEXT: subq {{.*}}(%rip), %rbp # 2380
# DISASM-PIC-NEXT: xorq {{.*}}(%rip), %r8 # 2380
# DISASM-PIC-NEXT: testq %r15, {{.*}}(%rip) # 2380

.data
.type bar, @object
Expand All @@ -78,6 +94,18 @@ bar:
.globl _start
.type _start, @function
_start:
## R_X86_64_GOTPCRELX
adcl bar@GOTPCREL(%rip), %eax
addl bar@GOTPCREL(%rip), %ebx
andl bar@GOTPCREL(%rip), %ecx
cmpl bar@GOTPCREL(%rip), %edx
orl bar@GOTPCREL(%rip), %edi
sbbl bar@GOTPCREL(%rip), %esi
subl bar@GOTPCREL(%rip), %ebp
xorl bar@GOTPCREL(%rip), %r8d
testl %r15d, bar@GOTPCREL(%rip)

## R_X86_64_REX_GOTPCRELX
adcq bar@GOTPCREL(%rip), %rax
addq bar@GOTPCREL(%rip), %rbx
andq bar@GOTPCREL(%rip), %rcx
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