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[lld-macho] Include branch extension thunks in linker map #120496

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Merged
merged 4 commits into from
Jan 8, 2025
Merged

[lld-macho] Include branch extension thunks in linker map #120496

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96693a1
[lld-macho] Include branch extension thunks in linker map
Dec 18, 2024
9537ec3
Remove unecessary variables from test file
Dec 18, 2024
95d49c6
Address feedback nr.1
Dec 19, 2024
62e7ef1
Address Feedback Nr.2
Dec 19, 2024
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15 changes: 11 additions & 4 deletions lld/MachO/ConcatOutputSection.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,8 +25,9 @@ class Defined;
// in the final binary.
class ConcatOutputSection : public OutputSection {
public:
explicit ConcatOutputSection(StringRef name)
: OutputSection(ConcatKind, name) {}
explicit ConcatOutputSection(StringRef name,
OutputSection::Kind kind = ConcatKind)
: OutputSection(kind, name) {}

const ConcatInputSection *firstSection() const { return inputs.front(); }
const ConcatInputSection *lastSection() const { return inputs.back(); }
Expand All @@ -46,7 +47,7 @@ class ConcatOutputSection : public OutputSection {
void writeTo(uint8_t *buf) const override;

static bool classof(const OutputSection *sec) {
return sec->kind() == ConcatKind;
return sec->kind() == ConcatKind || sec->kind() == TextKind;
}

static ConcatOutputSection *getOrCreateForInput(const InputSection *);
Expand All @@ -66,12 +67,18 @@ class ConcatOutputSection : public OutputSection {
// support thunk insertion.
class TextOutputSection : public ConcatOutputSection {
public:
explicit TextOutputSection(StringRef name) : ConcatOutputSection(name) {}
explicit TextOutputSection(StringRef name)
: ConcatOutputSection(name, TextKind) {}
void finalizeContents() override {}
void finalize() override;
bool needsThunks() const;
ArrayRef<ConcatInputSection *> getThunks() const { return thunks; }
void writeTo(uint8_t *buf) const override;

static bool classof(const OutputSection *sec) {
return sec->kind() == TextKind;
}

private:
uint64_t estimateStubsInRangeVA(size_t callIdx) const;

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21 changes: 20 additions & 1 deletion lld/MachO/MapFile.cpp
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Expand Up @@ -161,6 +161,20 @@ static uint64_t getSymSizeForMap(Defined *sym) {
return sym->size;
}

// Merges two vectors of input sections in order of their outSecOff values.
// This approach creates a new (temporary) vector which is not ideal but the
// ideal approach leads to a lot of code duplication.
static std::vector<ConcatInputSection *>
mergeOrderedInputs(ArrayRef<ConcatInputSection *> inputs1,
ArrayRef<ConcatInputSection *> inputs2) {
std::vector<ConcatInputSection *> vec(inputs1.size() + inputs2.size());
std::merge(inputs1.begin(), inputs1.end(), inputs2.begin(), inputs2.end(),
vec.begin(), [](ConcatInputSection *a, ConcatInputSection *b) {
return a->outSecOff < b->outSecOff;
});
return vec;
}

void macho::writeMapFile() {
if (config->mapFile.empty())
return;
Expand Down Expand Up @@ -220,7 +234,12 @@ void macho::writeMapFile() {
os << "# Address\tSize \tFile Name\n";
for (const OutputSegment *seg : outputSegments) {
for (const OutputSection *osec : seg->getSections()) {
if (auto *concatOsec = dyn_cast<ConcatOutputSection>(osec)) {
const TextOutputSection *textOsec = dyn_cast<TextOutputSection>(osec);
if (textOsec && textOsec->getThunks().size()) {
auto inputsAndThunks =
mergeOrderedInputs(textOsec->inputs, textOsec->getThunks());
printIsecArrSyms(inputsAndThunks);
} else if (auto *concatOsec = dyn_cast<ConcatOutputSection>(osec)) {
printIsecArrSyms(concatOsec->inputs);
} else if (osec == in.cStringSection || osec == in.objcMethnameSection) {
const auto &liveCStrings = info.liveCStringsForSection.lookup(osec);
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1 change: 1 addition & 0 deletions lld/MachO/OutputSection.h
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Expand Up @@ -37,6 +37,7 @@ class OutputSection {
enum Kind {
ConcatKind,
SyntheticKind,
TextKind,
};

OutputSection(Kind kind, StringRef name) : name(name), sectionKind(kind) {}
Expand Down
33 changes: 32 additions & 1 deletion lld/test/MachO/arm64-thunks.s
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Expand Up @@ -8,14 +8,45 @@
## (4) early calls to a dylib stub use a thunk, and later calls the stub
## directly
## (5) Thunks are created for all sections in the text segment with branches.
## (6) Thunks are in the linker map file.
## Notes:
## 0x4000000 = 64 Mi = half the magnitude of the forward-branch range

# RUN: rm -rf %t; mkdir %t
# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t/input.o
# RUN: %lld -arch arm64 -dead_strip -lSystem -U _extern_sym -o %t/thunk %t/input.o
# RUN: %lld -arch arm64 -dead_strip -lSystem -U _extern_sym -map %t/thunk.map -o %t/thunk %t/input.o
# RUN: llvm-objdump --no-print-imm-hex -d --no-show-raw-insn %t/thunk | FileCheck %s

## Check that the thunks appear in the map file and that everything is sorted by address
# Because of the `.space` instructions, there will end up being a lot of dead symbols in the linker map
# so generate a version of the linker map without dead symbols.
# RUN: awk '/# Dead Stripped Symbols:/ {exit} {print}' %t/thunk.map > %t/thunk_no_dead_syms.map
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@ellishg ellishg Dec 19, 2024

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I'm not sure I understand the point of this awk command. The last symbol you check is _z and then presumably there will be dead symbols after that. But the MAP check lines are done, so there is no problem?

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@alx32 alx32 Dec 19, 2024 •
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The issue is that because the .space. commands, linker map ends up being 2.7GB in size - with apparently each character added via .space being interpreted as a dead symbol (this might be another unrelated issue).

So the issue is that if the test were to break, then it would take a very very long time to complete (I didn't wait to fully time it) - trying to match the regex against the 2.7GB file.

This is just an optimization to have the test complete in a practical amount of time - even in case of failure.


# RUN: FileCheck %s --input-file %t/thunk_no_dead_syms.map --check-prefix=MAP

# MAP: [[ADDR1:0x[0-9A-Fa-f]+]] {{.*}} _b
# MAP-NEXT: [[ADDR2:0x[0-9A-Fa-f]+]] {{.*}} _c
# MAP-NEXT: [[ADDR3:0x[0-9A-Fa-f]+]] {{.*}} _d.thunk.0
# MAP-NEXT: [[ADDR4:0x[0-9A-Fa-f]+]] {{.*}} _e.thunk.0
# MAP-NEXT: [[ADDR5:0x[0-9A-Fa-f]+]] {{.*}} _f.thunk.0
# MAP-NEXT: [[ADDR6:0x[0-9A-Fa-f]+]] {{.*}} _g.thunk.0
# MAP-NEXT: [[ADDR7:0x[0-9A-Fa-f]+]] {{.*}} _h.thunk.0
# MAP-NEXT: [[ADDR8:0x[0-9A-Fa-f]+]] {{.*}} ___nan.thunk.0
# MAP-NEXT: [[ADDR9:0x[0-9A-Fa-f]+]] {{.*}} _d
# MAP-NEXT: [[ADDR10:0x[0-9A-Fa-f]+]] {{.*}} _e
# MAP-NEXT: [[ADDR11:0x[0-9A-Fa-f]+]] {{.*}} _f
# MAP-NEXT: [[ADDR12:0x[0-9A-Fa-f]+]] {{.*}} _g
# MAP-NEXT: [[ADDR13:0x[0-9A-Fa-f]+]] {{.*}} _a.thunk.0
# MAP-NEXT: [[ADDR14:0x[0-9A-Fa-f]+]] {{.*}} _b.thunk.0
# MAP-NEXT: [[ADDR15:0x[0-9A-Fa-f]+]] {{.*}} _h
# MAP-NEXT: [[ADDR16:0x[0-9A-Fa-f]+]] {{.*}} _main
# MAP-NEXT: [[ADDR17:0x[0-9A-Fa-f]+]] {{.*}} _c.thunk.0
# MAP-NEXT: [[ADDR18:0x[0-9A-Fa-f]+]] {{.*}} _d.thunk.1
# MAP-NEXT: [[ADDR19:0x[0-9A-Fa-f]+]] {{.*}} _e.thunk.1
# MAP-NEXT: [[ADDR20:0x[0-9A-Fa-f]+]] {{.*}} _f.thunk.1
# MAP-NEXT: [[ADDR21:0x[0-9A-Fa-f]+]] {{.*}} _z


# CHECK: Disassembly of section __TEXT,__text:

# CHECK: [[#%.13x, A_PAGE:]][[#%.3x, A_OFFSET:]] <_a>:
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