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[lld-macho] Support pc-relative section relocations 

Summary: So far we've only supported symbol relocations.

Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79211
This commit is contained in:
Jez Ng 2020-04-27 12:59:20 -07:00
parent 7bbdbacd00
commit 198b0c57df
5 changed files with 64 additions and 13 deletions
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12
lld/MachO/InputFiles.cpp
View File

@ -134,6 +134,7 @@ InputFile::parseSections(ArrayRef<section_64> sections) {
for (const section_64 &sec : sections) {
InputSection *isec = make<InputSection>();
isec->file = this;
isec->header = &sec;
isec->name = StringRef(sec.sectname, strnlen(sec.sectname, 16));
isec->segname = StringRef(sec.segname, strnlen(sec.segname, 16));
isec->data = {buf + sec.offset, static_cast<size_t>(sec.size)};
@ -165,11 +166,14 @@ void InputFile::parseRelocations(const section_64 &sec,
r.type = rel.r_type;
r.offset = rel.r_address;
r.addend = target->getImplicitAddend(buf + sec.offset + r.offset, r.type);
if (rel.r_extern)
if (rel.r_extern) {
r.target = symbols[rel.r_symbolnum];
else {
error("TODO: Non-extern relocations are not supported");
continue;
} else {
if (rel.r_symbolnum == 0 || rel.r_symbolnum > sections.size())
fatal("invalid section index in relocation for offset " +
std::to_string(r.offset) + " in section " + sec.sectname +
" of " + getName());
r.target = sections[rel.r_symbolnum - 1];
}
}
relocs.push_back(r);

11
lld/MachO/InputSection.cpp
View File

@ -32,6 +32,7 @@ void InputSection::writeTo(uint8_t *buf) {
for (Reloc &r : relocs) {
uint64_t va = 0;
uint64_t addend = r.addend;
if (auto *s = r.target.dyn_cast<Symbol *>()) {
if (auto *dylibSymbol = dyn_cast<DylibSymbol>(s)) {
va = target->getDylibSymbolVA(*dylibSymbol, r.type);
@ -40,11 +41,15 @@ void InputSection::writeTo(uint8_t *buf) {
}
} else if (auto *isec = r.target.dyn_cast<InputSection *>()) {
va = isec->getVA();
} else {
llvm_unreachable("Unknown relocation target");
// The implicit addend for pcrel section relocations is the pcrel offset
// in terms of the addresses in the input file. Here we adjust it so that
// it describes the offset from the start of the target section.
// TODO: Figure out what to do for non-pcrel section relocations.
// TODO: The offset of 4 is probably not right for ARM64.
addend -= isec->header->addr - (header->addr + r.offset + 4);
}
uint64_t val = va + r.addend;
uint64_t val = va + addend;
if (1) // TODO: handle non-pcrel relocations
val -= getVA() + r.offset;
target->relocateOne(buf + r.offset, r.type, val);

2
lld/MachO/InputSection.h
View File

@ -42,6 +42,8 @@ public:
InputFile *file = nullptr;
StringRef name;
StringRef segname;
// This provides access to the address of the section in the input file.
const llvm::MachO::section_64 *header;
OutputSection *parent = nullptr;
uint64_t outSecOff = 0;

23
lld/test/MachO/relocations.s
View File

@ -12,9 +12,12 @@
# CHECK-LABEL: <_main>:
## Test X86_64_RELOC_BRANCH
# CHECK: callq 0x[[#%x, F_ADDR]] <_f>
## Test X86_64_RELOC_SIGNED
## Test extern (symbol) X86_64_RELOC_SIGNED
# CHECK: leaq [[#%u, STR_OFF:]](%rip), %rsi
# CHECK-NEXT: [[#%x, CSTRING_ADDR - STR_OFF]]
## Test non-extern (section) X86_64_RELOC_SIGNED
# CHECK: leaq [[#%u, LSTR_OFF:]](%rip), %rsi
# CHECK-NEXT: [[#%x, CSTRING_ADDR + 22 - LSTR_OFF]]
.section __TEXT,__text
.globl _main, _f
@ -26,11 +29,21 @@ _main:
_f:
movl $0x2000004, %eax # write() syscall
mov $1, %rdi # stdout
leaq str(%rip), %rsi
mov $13, %rdx # length of str
leaq _str(%rip), %rsi
mov $21, %rdx # length of str
syscall
movl $0x2000004, %eax # write() syscall
mov $1, %rdi # stdout
leaq L_.str(%rip), %rsi
mov $15, %rdx # length of str
syscall
ret
.section __TEXT,__cstring
str:
.asciz "Hello world!\n"
## References to this generate a symbol relocation
_str:
.asciz "Local defined symbol\n"
## References to this generate a section relocation
L_.str:
.asciz "Private symbol\n"

29
lld/test/MachO/x86-64-reloc-signed.s
View File

@ -1,7 +1,7 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
# RUN: lld -flavor darwinnew -o %t %t.o
# RUN: llvm-objdump -d %t | FileCheck %s
# RUN: llvm-objdump -D %t | FileCheck %s
# CHECK: <_main>:
# CHECK-NEXT: movl {{.*}} # 2000 <_s>
@ -10,10 +10,18 @@
# CHECK-NEXT: callq {{.*}}
# CHECK-NEXT: movb {{.*}} # 2000 <_s>
# CHECK-NEXT: callq {{.*}}
# CHECK: <__not_text>:
# CHECK-NEXT: movl {{.*}} # 2005
# CHECK-NEXT: callq {{.*}}
# CHECK-NEXT: movl {{.*}} # 2007
# CHECK-NEXT: callq {{.*}}
# CHECK-NEXT: movb {{.*}} # 2005
# CHECK-NEXT: callq {{.*}}
.section __TEXT,__text
.globl _main
_main:
## Symbol relocations
movl $0x434241, _s(%rip) # X86_64_RELOC_SIGNED_4
callq _f
movl $0x44, _s+2(%rip) # X86_64_RELOC_SIGNED_2
@ -31,7 +39,26 @@ _f:
syscall
ret
.section __TEXT,__not_text
## Section relocations. We intentionally put them in a separate section since
## the __text section typically starts at an address of zero in object files,
## and so does not fully exercise the relocation logic.
movl $0x434241, L._s(%rip) # X86_64_RELOC_SIGNED_4
callq _f
movl $0x44, L._s+2(%rip) # X86_64_RELOC_SIGNED_2
callq _f
movb $0x45, L._s(%rip) # X86_64_RELOC_SIGNED_1
callq _f
ret
.section __DATA,__data
.globl _s
_s:
.space 5
## Create a new section to force the assembler to use a section relocation for
## the private symbol L._s. Otherwise, it will instead use a nearby non-private
## symbol to create a symbol relocation plus an addend.
.section __DATA,__foo
L._s:
.space 5