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[PowerPC] Support for R_PPC64_REL24_NOTOC calls where the caller has no TOC and the callee is not DSO local 

This patch supports the situation where caller does not have a valid TOC and
calls using the R_PPC64_REL24_NOTOC relocation and the callee is not DSO local.
In this case the call cannot be made directly since the callee may or may not
require a valid TOC pointer. As a result this situation require a PC-relative
plt stub to set up r12.

Reviewed By: sfertile, MaskRay, stefanp

Differential Revision: https://reviews.llvm.org/D83669
This commit is contained in:
Victor Huang 2020-07-29 18:38:55 +00:00
parent a1c9529e60
commit 8dbea4785c
4 changed files with 166 additions and 6 deletions
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5
lld/ELF/Arch/PPC64.cpp
View File

@ -1035,11 +1035,6 @@ bool PPC64::needsThunk(RelExpr expr, RelType type, const InputFile *file,
type != R_PPC64_REL24_NOTOC)
return false;
// FIXME: Remove the fatal error once the call protocol is implemented.
if (type == R_PPC64_REL24_NOTOC && s.isInPlt())
fatal("unimplemented feature: external function call with the reltype"
" R_PPC64_REL24_NOTOC");
// If a function is in the Plt it needs to be called with a call-stub.
if (s.isInPlt())
return true;

35
lld/ELF/Thunks.cpp
View File

@ -305,6 +305,21 @@ public:
void addSymbols(ThunkSection &isec) override;
};
// PPC64 PC-relative PLT Stub
// When a caller that does not maintain a toc-pointer performs an extern call
// then this stub is needed for:
// 1) Loading the target functions address from the procedure linkage table into
// r12 for use by the target functions global entry point, and into the count
// register with pc-relative instructions.
// 2) Transferring control to the target function through an indirect branch.
class PPC64PCRelPLTStub final : public Thunk {
public:
PPC64PCRelPLTStub(Symbol &dest) : Thunk(dest, 0) {}
uint32_t size() override { return 16; }
void writeTo(uint8_t *buf) override;
void addSymbols(ThunkSection &isec) override;
};
// A bl instruction uses a signed 24 bit offset, with an implicit 4 byte
// alignment. This gives a possible 26 bits of 'reach'. If the call offset is
// larger then that we need to emit a long-branch thunk. The target address
@ -880,6 +895,23 @@ void PPC64R12SetupStub::addSymbols(ThunkSection &isec) {
isec);
}
void PPC64PCRelPLTStub::writeTo(uint8_t *buf) {
int64_t offset = destination.getGotPltVA() - getThunkTargetSym()->getVA();
if (!isInt<34>(offset))
fatal("offset must fit in 34 bits to encode in the instruction");
uint64_t pld =
PLD_R12_NO_DISP | (((offset >> 16) & 0x3ffff) << 32) | (offset & 0xffff);
writePrefixedInstruction(buf + 0, pld); // pld r12, func@plt@pcrel
write32(buf + 8, MTCTR_R12); // mtctr r12
write32(buf + 12, BCTR); // bctr
}
void PPC64PCRelPLTStub::addSymbols(ThunkSection &isec) {
addSymbol(saver.save("__plt_pcrel_" + destination.getName()), STT_FUNC, 0,
isec);
}
void PPC64LongBranchThunk::writeTo(uint8_t *buf) {
int64_t offset = in.ppc64LongBranchTarget->getEntryVA(&destination, addend) -
getPPC64TocBase();
@ -1007,7 +1039,8 @@ static Thunk *addThunkPPC64(RelType type, Symbol &s, int64_t a) {
type == R_PPC64_REL24_NOTOC) &&
"unexpected relocation type for thunk");
if (s.isInPlt())
return make<PPC64PltCallStub>(s);
return type == R_PPC64_REL24_NOTOC ? (Thunk *)make<PPC64PCRelPLTStub>(s)
: (Thunk *)make<PPC64PltCallStub>(s);
// This check looks at the st_other bits of the callee. If the value is 1
// then the callee clobbers the TOC and we need an R2 save stub.

131
lld/test/ELF/ppc64-pcrel-call-to-extern.s Normal file
View File

@ -0,0 +1,131 @@
# REQUIRES: ppc
# RUN: echo 'SECTIONS { \
# RUN: .text_caller1 0x10010000 : { *(.text_caller1) } \
# RUN: .text_caller2 0x10020000 : { *(.text_caller2) } \
# RUN: .text_caller3 0x10030000 : { *(.text_caller3) } \
# RUN: }' > %t.script
# RUN: llvm-mc -filetype=obj -triple=powerpc64le --defsym AUX=1 %s -o %t1.o
# RUN: llvm-mc -filetype=obj -triple=powerpc64le %s -o %t2.o
# RUN: ld.lld --shared %t2.o -o %t2.so
# RUN: ld.lld -T %t.script %t1.o %t2.so -o %t
# RUN: llvm-readelf -s %t | FileCheck %s --check-prefix=SYMBOL
# RUN: llvm-readelf -S -d %t | FileCheck %s --check-prefix=SEC
# RUN: llvm-readobj -r %t | FileCheck %s --check-prefix=REL
# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t | FileCheck %s
# RUN: llvm-mc -filetype=obj -triple=powerpc64 --defsym AUX=1 %s -o %t1.o
# RUN: llvm-mc -filetype=obj -triple=powerpc64 %s -o %t2.o
# RUN: ld.lld --shared %t2.o -o %t2.so
# RUN: ld.lld -T %t.script %t1.o %t2.so -o %t
# RUN: llvm-readelf -s %t | FileCheck %s --check-prefix=SYMBOL
# RUN: llvm-readelf -S -d %t | FileCheck %s --check-prefix=SEC
# RUN: llvm-readobj -r %t | FileCheck %s --check-prefix=REL
# RUN: llvm-objdump -d --no-show-raw-insn --mcpu=pwr10 %t | FileCheck %s
## The test is created to check that when a function without TOC access an
## external function, a r12 setup stub is inserted.
# SYMBOL: Symbol table '.dynsym' contains 4 entries:
# SYMBOL: 1: 0000000000000000 0 NOTYPE GLOBAL DEFAULT [<other: 0x60>] UND callee_global_TOC
# SYMBOL-NEXT: 2: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND callee_global_stother0
# SYMBOL-NEXT: 3: 0000000000000000 0 NOTYPE GLOBAL DEFAULT [<other: 0x20>] UND callee_global_stother1
# SYMBOL: Symbol table '.symtab' contains 12 entries:
# SYMBOL: 2: 0000000010010000 0 NOTYPE LOCAL DEFAULT [<other: 0x20>] 6 caller1
# SYMBOL-NEXT: 3: 0000000010020000 0 NOTYPE LOCAL DEFAULT [<other: 0x20>] 7 caller2
# SYMBOL-NEXT: 4: 0000000010030000 0 NOTYPE LOCAL DEFAULT [<other: 0x20>] 8 caller3
# SYMBOL: 6: 0000000010010008 16 FUNC LOCAL DEFAULT 6 __plt_pcrel_callee_global_stother0
# SYMBOL-NEXT: 7: 0000000010020008 16 FUNC LOCAL DEFAULT 7 __plt_pcrel_callee_global_stother1
# SYMBOL-NEXT: 8: 0000000010030008 16 FUNC LOCAL DEFAULT 8 __plt_pcrel_callee_global_TOC
# SYMBOL-NEXT: 9: 0000000000000000 0 NOTYPE GLOBAL DEFAULT [<other: 0x60>] UND callee_global_TOC
# SYMBOL-NEXT: 10: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND callee_global_stother0
# SYMBOL-NEXT: 11: 0000000000000000 0 NOTYPE GLOBAL DEFAULT [<other: 0x20>] UND callee_global_stother1
## DT_PLTGOT points to .plt
# SEC: .plt NOBITS 0000000010030140 040140 000028 00 WA 0 0 8
# SEC: 0x0000000000000003 (PLTGOT) 0x10030140
## The first 2 entries in the .plt are reserved for the dynamic linkers
## usage. The JMP_SLOT relocations are stored at .plt[2], .plt[3], .plt[4].
## Check that we emit 3 R_PPC64_JMP_SLOT in .rela.plt.
# REL: .rela.plt {
# REL-NEXT: 0x10030150 R_PPC64_JMP_SLOT callee_global_stother0 0x0
# REL-NEXT: 0x10030158 R_PPC64_JMP_SLOT callee_global_stother1 0x0
# REL-NEXT: 0x10030160 R_PPC64_JMP_SLOT callee_global_TOC 0x0
# REL-NEXT: }
# CHECK-LABEL: <caller1>:
# CHECK: 10010000: bl 0x10010008
# CHECK-NEXT: 10010004: blr
## .plt[2] - 0x10010008 = 0x10030150 - 0x10010008 = 0x20148 = 131400
# CHECK-LABEL: <__plt_pcrel_callee_global_stother0>:
# CHECK: 10010008: pld 12, 131400(0), 1
# CHECK-NEXT: 10010010: mtctr 12
# CHECK-NEXT: 10010014: bctr
# CHECK-LABEL: <caller2>:
# CHECK: 10020000: bl 0x10020008
# CHECK-NEXT: 10020004: blr
## .plt[3] - 0x10020008 = 0x10030158 - 0x10020008 = 0x10150 = 65872
# CHECK-LABEL: <__plt_pcrel_callee_global_stother1>:
# CHECK: 10020008: pld 12, 65872(0), 1
# CHECK-NEXT: 10020010: mtctr 12
# CHECK-NEXT: 10020014: bctr
# CHECK-LABEL: <caller3>:
# CHECK: 10030000: bl 0x10030008
# CHECK-NEXT: 10030004: blr
## .plt[4] - 0x10030008 = 0x10030160 - 0x10030008 = 0x158 = 344
# CHECK-LABEL: <__plt_pcrel_callee_global_TOC>:
# CHECK: 10030008: pld 12, 344(0), 1
# CHECK-NEXT: 10030010: mtctr 12
# CHECK-NEXT: 10030014: bctr
.ifdef AUX
.section .text_caller1, "ax", %progbits
caller1:
.localentry caller1, 1
bl callee_global_stother0@notoc
blr
.section .text_caller2, "ax", %progbits
caller2:
.localentry caller2, 1
bl callee_global_stother1@notoc
blr
.section .text_caller3, "ax", %progbits
caller3:
.localentry caller3, 1
bl callee_global_TOC@notoc
blr
.else
func_extern:
blr
.globl callee_global_stother0
callee_global_stother0:
blr
.globl callee_global_stother1
callee_global_stother1:
.localentry callee_global_stother1, 1
## nop is not needed after bl for R_PPC64_REL24_NOTOC
bl func_extern@notoc
blr
.globl callee_global_TOC
callee_global_TOC:
.Lfunc_gep1:
addis 2, 12, .TOC.-.Lfunc_gep1@ha
addi 2, 2, .TOC.-.Lfunc_gep1@l
.Lfunc_lep1:
.localentry callee_global_TOC, .Lfunc_lep1-.Lfunc_gep1
addis 4, 2, global@toc@ha
lwz 3, global@toc@l(4)
blr
global:
.long 0
.size global, 4
.endif

1
llvm/include/llvm/Object/ELF.h
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@ -50,6 +50,7 @@ static inline Error createError(const Twine &Err) {
enum PPCInstrMasks : uint64_t {
PADDI_R12_NO_DISP = 0x0610000039800000,
PLD_R12_NO_DISP = 0x04100000E5800000,
MTCTR_R12 = 0x7D8903A6,
BCTR = 0x4E800420,
};