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[ELF][PPC32] Support range extension thunks with addends
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* Generalize the code added in D70637 and D70937. We should eventually remove the EM_MIPS special case.
* Handle R_PPC_LOCAL24PC the same way as R_PPC_REL24.

Reviewed By: Bdragon28

Differential Revision: https://reviews.llvm.org/D73424

(cherry picked from commit 70389be)
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@MaskRay
MaskRay committed Jan 26, 2020
1 parent 6f8ad14 commit f15b60b
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Showing 4 changed files with 140 additions and 23 deletions.
10 changes: 5 additions & 5 deletions lld/ELF/Arch/PPC.cpp
View file
Expand Up @@ -193,21 +193,21 @@ void PPC::writeGotPlt(uint8_t *buf, const Symbol &s) const {
}

bool PPC::needsThunk(RelExpr expr, RelType type, const InputFile *file,
uint64_t branchAddr, const Symbol &s, int64_t /*a*/) const {
if (type != R_PPC_REL24 && type != R_PPC_PLTREL24)
uint64_t branchAddr, const Symbol &s, int64_t a) const {
if (type != R_PPC_LOCAL24PC && type != R_PPC_REL24 && type != R_PPC_PLTREL24)
return false;
if (s.isInPlt())
return true;
if (s.isUndefWeak())
return false;
return !(expr == R_PC && PPC::inBranchRange(type, branchAddr, s.getVA()));
return !PPC::inBranchRange(type, branchAddr, s.getVA(a));
}

uint32_t PPC::getThunkSectionSpacing() const { return 0x2000000; }

bool PPC::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
uint64_t offset = dst - src;
if (type == R_PPC_REL24 || type == R_PPC_PLTREL24)
if (type == R_PPC_LOCAL24PC || type == R_PPC_REL24 || type == R_PPC_PLTREL24)
return isInt<26>(offset);
llvm_unreachable("unsupported relocation type used in branch");
}
Expand All @@ -230,13 +230,13 @@ RelExpr PPC::getRelExpr(RelType type, const Symbol &s,
return R_DTPREL;
case R_PPC_REL14:
case R_PPC_REL32:
case R_PPC_LOCAL24PC:
case R_PPC_REL16_LO:
case R_PPC_REL16_HI:
case R_PPC_REL16_HA:
return R_PC;
case R_PPC_GOT16:
return R_GOT_OFF;
case R_PPC_LOCAL24PC:
case R_PPC_REL24:
return R_PLT_PC;
case R_PPC_PLTREL24:
Expand Down
21 changes: 7 additions & 14 deletions lld/ELF/Relocations.cpp
View file
Expand Up @@ -1304,10 +1304,10 @@ static void scanReloc(InputSectionBase &sec, OffsetGetter &getOffset, RelTy *&i,
if (expr == R_GOT_PC && !isAbsoluteValue(sym)) {
expr = target->adjustRelaxExpr(type, relocatedAddr, expr);
} else {
// Addend of R_PPC_PLTREL24 is used to choose call stub type. It should be
// ignored if optimized to R_PC.
// The 0x8000 bit of r_addend of R_PPC_PLTREL24 is used to choose call
// stub type. It should be ignored if optimized to R_PC.
if (config->emachine == EM_PPC && expr == R_PPC32_PLTREL)
addend = 0;
addend &= ~0x8000;
expr = fromPlt(expr);
}
}
Expand Down Expand Up @@ -1826,9 +1826,7 @@ bool ThunkCreator::normalizeExistingThunk(Relocation &rel, uint64_t src) {
rel.sym->getVA(rel.addend) + getPCBias(rel.type)))
return true;
rel.sym = &t->destination;
// TODO Restore addend on all targets.
if (config->emachine == EM_AARCH64 || config->emachine == EM_PPC64)
rel.addend = t->addend;
rel.addend = t->addend;
if (rel.sym->isInPlt())
rel.expr = toPlt(rel.expr);
}
Expand Down Expand Up @@ -1906,16 +1904,11 @@ bool ThunkCreator::createThunks(ArrayRef<OutputSection *> outputSections) {
rel.sym = t->getThunkTargetSym();
rel.expr = fromPlt(rel.expr);

// On AArch64 and PPC64, a jump/call relocation may be encoded as
// On AArch64 and PPC, a jump/call relocation may be encoded as
// STT_SECTION + non-zero addend, clear the addend after
// redirection.
//
// The addend of R_PPC_PLTREL24 should be ignored after changing to
// R_PC.
if (config->emachine == EM_AARCH64 ||
config->emachine == EM_PPC64 ||
(config->emachine == EM_PPC && rel.type == R_PPC_PLTREL24))
rel.addend = 0;
if (config->emachine != EM_MIPS)
rel.addend = -getPCBias(rel.type);
}

for (auto &p : isd->thunkSections)
Expand Down
45 changes: 41 additions & 4 deletions lld/ELF/Thunks.cpp
View file
Expand Up @@ -245,8 +245,7 @@ class PPC32PltCallStub final : public Thunk {
// decide the offsets in the call stub.
PPC32PltCallStub(const InputSection &isec, const Relocation &rel,
Symbol &dest)
: Thunk(dest, rel.type == R_PPC_PLTREL24 ? rel.addend : 0),
file(isec.file) {}
: Thunk(dest, rel.addend), file(isec.file) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
Expand All @@ -257,6 +256,14 @@ class PPC32PltCallStub final : public Thunk {
const InputFile *file;
};

class PPC32LongThunk final : public Thunk {
public:
PPC32LongThunk(Symbol &dest, int64_t addend) : Thunk(dest, addend) {}
uint32_t size() override { return config->isPic ? 32 : 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};

// PPC64 Plt call stubs.
// Any call site that needs to call through a plt entry needs a call stub in
// the .text section. The call stub is responsible for:
Expand Down Expand Up @@ -765,6 +772,33 @@ bool PPC32PltCallStub::isCompatibleWith(const InputSection &isec,
return !config->isPic || (isec.file == file && rel.addend == addend);
}

void PPC32LongThunk::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__LongThunk_" + destination.getName()), STT_FUNC, 0,
isec);
}

void PPC32LongThunk::writeTo(uint8_t *buf) {
auto ha = [](uint32_t v) -> uint16_t { return (v + 0x8000) >> 16; };
auto lo = [](uint32_t v) -> uint16_t { return v; };
uint32_t d = destination.getVA(addend);
if (config->isPic) {
uint32_t off = d - (getThunkTargetSym()->getVA() + 8);
write32(buf + 0, 0x7c0802a6); // mflr r12,0
write32(buf + 4, 0x429f0005); // bcl r20,r31,.+4
write32(buf + 8, 0x7d8802a6); // mtctr r12
write32(buf + 12, 0x3d8c0000 | ha(off)); // addis r12,r12,off@ha
write32(buf + 16, 0x398c0000 | lo(off)); // addi r12,r12,off@l
write32(buf + 20, 0x7c0803a6); // mtlr r0
buf += 24;
} else {
write32(buf + 0, 0x3d800000 | ha(d)); // lis r12,d@ha
write32(buf + 4, 0x398c0000 | lo(d)); // addi r12,r12,d@l
buf += 8;
}
write32(buf + 0, 0x7d8903a6); // mtctr r12
write32(buf + 4, 0x4e800420); // bctr
}

void writePPC64LoadAndBranch(uint8_t *buf, int64_t offset) {
uint16_t offHa = (offset + 0x8000) >> 16;
uint16_t offLo = offset & 0xffff;
Expand Down Expand Up @@ -902,9 +936,12 @@ static Thunk *addThunkMips(RelType type, Symbol &s) {

static Thunk *addThunkPPC32(const InputSection &isec, const Relocation &rel,
Symbol &s) {
assert((rel.type == R_PPC_REL24 || rel.type == R_PPC_PLTREL24) &&
assert((rel.type == R_PPC_LOCAL24PC || rel.type == R_PPC_REL24 ||
rel.type == R_PPC_PLTREL24) &&
"unexpected relocation type for thunk");
return make<PPC32PltCallStub>(isec, rel, s);
if (s.isInPlt())
return make<PPC32PltCallStub>(isec, rel, s);
return make<PPC32LongThunk>(s, rel.addend);
}

static Thunk *addThunkPPC64(RelType type, Symbol &s, int64_t a) {
Expand Down
87 changes: 87 additions & 0 deletions lld/test/ELF/ppc32-long-thunk.s
View file
@@ -0,0 +1,87 @@
# REQUIRES: ppc
# RUN: echo 'SECTIONS { \
# RUN: .text_low 0x2000: { *(.text_low) } \
# RUN: .text_high 0x2002000 : { *(.text_high) } \
# RUN: }' > %t.script

# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
# RUN: ld.lld -T %t.script %t.o -o %t
# RUN: llvm-readelf -r %t | FileCheck --check-prefix=SEC %s
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefixes=CHECK,PD %s

# RUN: ld.lld -T %t.script -pie %t.o -o %t
# RUN: llvm-readelf -r %t | FileCheck --check-prefix=SEC %s
# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck --check-prefixes=CHECK,PI %s

# SEC: There are no relocations in this file.

# CHECK: _start:
# CHECK-NEXT: 2000: bl .+24
# CHECK-NEXT: bl .+20
# CHECK-NEXT: bl .+16
# CHECK-NEXT: bl .+33554428
# PD-NEXT: bl .+24
# PI-NEXT: bl .+40

## high = 0x02002008 = 65536*512+8200
# PD: __LongThunk_high:
# PD-NEXT: 2018: lis 12, 512
# PD-NEXT: addi 12, 12, 8200
# PD-NEXT: mtctr 12
# PD-NEXT: bctr

## .text_high+16 = 0x02002010 = 65536*512+8208
# PD: __LongThunk_:
# PD-NEXT: 2028: lis 12, 512
# PD-NEXT: addi 12, 12, 8208
# PD-NEXT: mtctr 12
# PD-NEXT: bctr

## high-0x2028 = 0x02002008-0x2020 = 65536*512-24
# PI: __LongThunk_high:
# PI-NEXT: 2018: mflr 0
# PI-NEXT: bcl 20, 31, .+4
# PI-NEXT: 2020: mflr 12
# PI-NEXT: addis 12, 12, 512
# PI-NEXT: addi 12, 12, -24
# PI-NEXT: mtlr 0
# PI-NEXT: mtctr 12
# PI-NEXT: bctr

## .text_high+16-0x2048 = 0x02002010-0x2048 = 65536*512-48
# PI: __LongThunk_:
# PI-NEXT: 2038: mflr 0
# PI-NEXT: bcl 20, 31, .+4
# PI-NEXT: 2040: mflr 12
# PI-NEXT: addis 12, 12, 512
# PI-NEXT: addi 12, 12, -48
# PI-NEXT: mtlr 0
# PI-NEXT: mtctr 12
# PI-NEXT: bctr

.section .text_low, "ax", %progbits
.globl _start
_start:
bl high@local # Need a thunk
bl high@local # Need a thunk
bl high+32768@plt # Need a thunk
bl high
bl .text_high+16 # Need a thunk
blr

# PD: 02002008 high:
# PD-NEXT: bl .-33554432
# PD-NEXT: bl .+4
# PD: __LongThunk_:
# PD-NEXT: 2002010: lis 12, 0
# PD-NEXT: addi 12, 12, 8200
# PD-NEXT: mtctr 12
# PD-NEXT: bctr

.section .text_high, "ax", %progbits
nop
nop
.globl high
high:
bl .text_low+8
bl .text_low+8 # Need a thunk

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