[lld] b422dac - [lld-macho][reland] Support EH frames under arm64
Jez Ng via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 13 04:47:31 PDT 2022
Author: Jez Ng
Date: 2022-06-13T07:45:27-04:00
New Revision: b422dac240f1475999a2c1b5fc242a0ef2e08727
URL: https://github.com/llvm/llvm-project/commit/b422dac240f1475999a2c1b5fc242a0ef2e08727
DIFF: https://github.com/llvm/llvm-project/commit/b422dac240f1475999a2c1b5fc242a0ef2e08727.diff
LOG: [lld-macho][reland] Support EH frames under arm64
This reverts commit 10641a42e2286679e0d36ca827e1a40d95ae8ef1.
Differential Revision: https://reviews.llvm.org/D124561
Added:
lld/test/MachO/Inputs/eh-frame-arm64-r.o
Modified:
lld/MachO/InputFiles.cpp
lld/test/MachO/eh-frame.s
Removed:
################################################################################
diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
index 16d019fb477bd..89405d21878a2 100644
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -1172,16 +1172,37 @@ static CIE parseCIE(const InputSection *isec, const EhReader &reader,
//
// Concretely, we expect our relocations to write the value of `PC -
// target_addr` to `PC`. `PC` itself is denoted by a minuend relocation that
-// points to a symbol or section plus an addend.
+// points to a symbol plus an addend.
+//
+// It is important that the minuend relocation point to a symbol within the
+// same section as the fixup value, since sections may get moved around.
+//
+// For example, for arm64, llvm-mc emits relocations for the target function
+// address like so:
+//
+// ltmp:
+// <CIE start>
+// ...
+// <CIE end>
+// ... multiple FDEs ...
+// <FDE start>
+// <target function address - (ltmp + pcrel offset)>
+// ...
+//
+// If any of the FDEs in `multiple FDEs` get dead-stripped, then `FDE start`
+// will move to an earlier address, and `ltmp + pcrel offset` will no longer
+// reflect an accurate pcrel value. To avoid this problem, we "canonicalize"
+// our relocation by adding an `EH_Frame` symbol at `FDE start`, and updating
+// the reloc to be `target function address - (EH_Frame + new pcrel offset)`.
//
// If `Invert` is set, then we instead expect `target_addr - PC` to be written
// to `PC`.
template <bool Invert = false>
Defined *
-getTargetSymbolFromSubtraction(const InputSection *isec,
- std::vector<macho::Reloc>::iterator relocIt) {
- const macho::Reloc &subtrahend = *relocIt;
- const macho::Reloc &minuend = *std::next(relocIt);
+targetSymFromCanonicalSubtractor(const InputSection *isec,
+ std::vector<macho::Reloc>::iterator relocIt) {
+ macho::Reloc &subtrahend = *relocIt;
+ macho::Reloc &minuend = *std::next(relocIt);
assert(target->hasAttr(subtrahend.type, RelocAttrBits::SUBTRAHEND));
assert(target->hasAttr(minuend.type, RelocAttrBits::UNSIGNED));
// Note: pcSym may *not* be exactly at the PC; there's usually a non-zero
@@ -1196,9 +1217,21 @@ getTargetSymbolFromSubtraction(const InputSection *isec,
}
if (Invert)
std::swap(pcSym, target);
- if (pcSym->isec != isec ||
- pcSym->value - (Invert ? -1 : 1) * minuend.addend != subtrahend.offset)
- fatal("invalid FDE relocation in __eh_frame");
+ if (pcSym->isec == isec) {
+ if (pcSym->value - (Invert ? -1 : 1) * minuend.addend != subtrahend.offset)
+ fatal("invalid FDE relocation in __eh_frame");
+ } else {
+ // Ensure the pcReloc points to a symbol within the current EH frame.
+ // HACK: we should really verify that the original relocation's semantics
+ // are preserved. In particular, we should have
+ // `oldSym->value + oldOffset == newSym + newOffset`. However, we don't
+ // have an easy way to access the offsets from this point in the code; some
+ // refactoring is needed for that.
+ macho::Reloc &pcReloc = Invert ? minuend : subtrahend;
+ pcReloc.referent = isec->symbols[0];
+ assert(isec->symbols[0]->value == 0);
+ minuend.addend = pcReloc.offset * (Invert ? 1LL : -1LL);
+ }
return target;
}
@@ -1255,7 +1288,7 @@ void ObjFile::registerEhFrames(Section &ehFrameSection) {
if (cieOffRelocIt != isec->relocs.end()) {
// We already have an explicit relocation for the CIE offset.
cieIsec =
- getTargetSymbolFromSubtraction</*Invert=*/true>(isec, cieOffRelocIt)
+ targetSymFromCanonicalSubtractor</*Invert=*/true>(isec, cieOffRelocIt)
->isec;
dataOff += sizeof(uint32_t);
} else {
@@ -1310,7 +1343,7 @@ void ObjFile::registerEhFrames(Section &ehFrameSection) {
Defined *funcSym;
if (funcAddrRelocIt != isec->relocs.end()) {
- funcSym = getTargetSymbolFromSubtraction(isec, funcAddrRelocIt);
+ funcSym = targetSymFromCanonicalSubtractor(isec, funcAddrRelocIt);
} else {
funcSym = findSymbolAtAddress(sections, funcAddr);
ehRelocator.makePcRel(funcAddrOff, funcSym, target->p2WordSize);
@@ -1325,7 +1358,7 @@ void ObjFile::registerEhFrames(Section &ehFrameSection) {
InputSection *lsdaIsec = nullptr;
if (lsdaAddrRelocIt != isec->relocs.end()) {
- lsdaIsec = getTargetSymbolFromSubtraction(isec, lsdaAddrRelocIt)->isec;
+ lsdaIsec = targetSymFromCanonicalSubtractor(isec, lsdaAddrRelocIt)->isec;
} else if (lsdaAddrOpt) {
uint64_t lsdaAddr = *lsdaAddrOpt;
Section *sec = findContainingSection(sections, &lsdaAddr);
diff --git a/lld/test/MachO/Inputs/eh-frame-arm64-r.o b/lld/test/MachO/Inputs/eh-frame-arm64-r.o
new file mode 100644
index 0000000000000..15e73cacf71d0
Binary files /dev/null and b/lld/test/MachO/Inputs/eh-frame-arm64-r.o
diff er
diff --git a/lld/test/MachO/eh-frame.s b/lld/test/MachO/eh-frame.s
index 24fd7bfc93f97..7437fdddbc0a3 100644
--- a/lld/test/MachO/eh-frame.s
+++ b/lld/test/MachO/eh-frame.s
@@ -20,6 +20,18 @@
# RUN: llvm-nm -m %t/eh-frame-x86_64-r | FileCheck %s --check-prefix NO-EH-SYMS
# RUN: llvm-readobj --section-headers %t/eh-frame-x86_64-r | FileCheck %s --check-prefix=ALIGN -D#ALIGN=3
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-macos11.0 %s -o %t/eh-frame-arm64.o
+# RUN: %lld -arch arm64 -lSystem -lc++ %t/eh-frame-arm64.o -o %t/eh-frame-arm64
+# RUN: llvm-objdump --macho --syms --indirect-symbols --unwind-info \
+# RUN: --dwarf=frames %t/eh-frame-arm64 | FileCheck %s -D#BASE=0x100000000 -D#DWARF_ENC=3
+# RUN: llvm-nm -m %t/eh-frame-arm64 | FileCheck %s --check-prefix NO-EH-SYMS
+
+# COM: ld -r %t/eh-frame-arm64.o -o %S/Inputs/eh-frame-arm64-r.o
+# RUN: %lld -arch arm64 -lSystem -lc++ %S/Inputs/eh-frame-arm64-r.o -o %t/eh-frame-arm64-r
+# RUN: llvm-objdump --macho --syms --indirect-symbols --unwind-info \
+# RUN: --dwarf=frames %t/eh-frame-arm64-r | FileCheck %s -D#BASE=0x100000000 -D#DWARF_ENC=3
+# RUN: llvm-nm -m %t/eh-frame-arm64-r | FileCheck %s --check-prefix NO-EH-SYMS
+
# ALIGN: Name: __eh_frame
# ALIGN-NEXT: Segment: __TEXT
# ALIGN-NEXT: Address:
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