[lld] 6c641d0 - [lld-macho] Handle user-provided dtrace symbols to avoid linking failure
Jez Ng via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 11 12:32:35 PDT 2022
Author: Kaining Zhong
Date: 2022-07-11T15:32:26-04:00
New Revision: 6c641d0de686efd3e3da055aa4c743bb3450acb7
URL: https://github.com/llvm/llvm-project/commit/6c641d0de686efd3e3da055aa4c743bb3450acb7
DIFF: https://github.com/llvm/llvm-project/commit/6c641d0de686efd3e3da055aa4c743bb3450acb7.diff
LOG: [lld-macho] Handle user-provided dtrace symbols to avoid linking failure
This fixes https://github.com/llvm/llvm-project/issues/56238. ld64.lld currently does not generate __dof section in Mach-O, and -no_dtrace_dof option is on by default. However when there are user-defined dtrace symbols, ld64.lld will treat them as undefined symbols, which causes the linking to fail because lld cannot find their definitions. This patch allows ld64.lld to rewrite the instructions calling dtrace symbols to instructions like nop as what ld64 does; therefore, when encountered with user-provided dtrace probes, the linking can still succeed.
I'm not sure whether support for dtrace is expected in lld, so for now I didn't add codes to make lld emit __dof section like ld64, and only made it possible to link with dtrace symbols provided. If this feature is needed, I can add that part in Dtrace.cpp & Dtrace.h.
Reviewed By: int3, #lld-macho
Differential Revision: https://reviews.llvm.org/D129062
Added:
lld/test/MachO/arm-dtrace.s
lld/test/MachO/arm64-32-dtrace.s
lld/test/MachO/arm64-dtrace.s
lld/test/MachO/x86_64-dtrace.s
Modified:
lld/MachO/Arch/ARM.cpp
lld/MachO/Arch/ARM64Common.cpp
lld/MachO/Arch/ARM64Common.h
lld/MachO/Arch/X86_64.cpp
lld/MachO/InputSection.cpp
lld/MachO/SymbolTable.cpp
lld/MachO/Target.h
Removed:
################################################################################
diff --git a/lld/MachO/Arch/ARM.cpp b/lld/MachO/Arch/ARM.cpp
index 7de0837fcf38a..fd215ed99b593 100644
--- a/lld/MachO/Arch/ARM.cpp
+++ b/lld/MachO/Arch/ARM.cpp
@@ -40,6 +40,9 @@ struct ARM : TargetInfo {
void relaxGotLoad(uint8_t *loc, uint8_t type) const override;
const RelocAttrs &getRelocAttrs(uint8_t type) const override;
uint64_t getPageSize() const override { return 4 * 1024; }
+
+ void handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const override;
};
} // namespace
@@ -170,3 +173,36 @@ TargetInfo *macho::createARMTargetInfo(uint32_t cpuSubtype) {
static ARM t(cpuSubtype);
return &t;
}
+
+void ARM::handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const {
+ if (config->outputType == MH_OBJECT)
+ return;
+
+ switch (r.type) {
+ case ARM_RELOC_BR24:
+ if (sym->getName().startswith("___dtrace_probe")) {
+ // change call site to a NOP
+ write32le(loc, 0xE1A00000);
+ } else if (sym->getName().startswith("___dtrace_isenabled")) {
+ // change call site to 'eor r0, r0, r0'
+ write32le(loc, 0xE0200000);
+ } else {
+ error("Unrecognized dtrace symbol prefix: " + toString(*sym));
+ }
+ break;
+ case ARM_THUMB_RELOC_BR22:
+ if (sym->getName().startswith("___dtrace_probe")) {
+ // change 32-bit blx call site to two thumb NOPs
+ write32le(loc, 0x46C046C0);
+ } else if (sym->getName().startswith("___dtrace_isenabled")) {
+ // change 32-bit blx call site to 'nop', 'eor r0, r0'
+ write32le(loc, 0x46C04040);
+ } else {
+ error("Unrecognized dtrace symbol prefix: " + toString(*sym));
+ }
+ break;
+ default:
+ llvm_unreachable("Unsupported dtrace relocation type for ARM");
+ }
+}
diff --git a/lld/MachO/Arch/ARM64Common.cpp b/lld/MachO/Arch/ARM64Common.cpp
index f55258ce8ec9f..27fdf4ba14d93 100644
--- a/lld/MachO/Arch/ARM64Common.cpp
+++ b/lld/MachO/Arch/ARM64Common.cpp
@@ -109,3 +109,21 @@ void ARM64Common::relaxGotLoad(uint8_t *loc, uint8_t type) const {
instruction = ((instruction & 0x001fffff) | 0x91000000);
write32le(loc, instruction);
}
+
+void ARM64Common::handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const {
+ assert(r.type == ARM64_RELOC_BRANCH26);
+
+ if (config->outputType == MH_OBJECT)
+ return;
+
+ if (sym->getName().startswith("___dtrace_probe")) {
+ // change call site to a NOP
+ write32le(loc, 0xD503201F);
+ } else if (sym->getName().startswith("___dtrace_isenabled")) {
+ // change call site to 'MOVZ X0,0'
+ write32le(loc, 0xD2800000);
+ } else {
+ error("Unrecognized dtrace symbol prefix: " + toString(*sym));
+ }
+}
diff --git a/lld/MachO/Arch/ARM64Common.h b/lld/MachO/Arch/ARM64Common.h
index 54f94ee76c06b..1bd85066b35a8 100644
--- a/lld/MachO/Arch/ARM64Common.h
+++ b/lld/MachO/Arch/ARM64Common.h
@@ -29,6 +29,9 @@ struct ARM64Common : TargetInfo {
void relaxGotLoad(uint8_t *loc, uint8_t type) const override;
uint64_t getPageSize() const override { return 16 * 1024; }
+
+ void handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const override;
};
inline uint64_t bitField(uint64_t value, int right, int width, int left) {
diff --git a/lld/MachO/Arch/X86_64.cpp b/lld/MachO/Arch/X86_64.cpp
index d675356b9ffb9..d2efa5bb34514 100644
--- a/lld/MachO/Arch/X86_64.cpp
+++ b/lld/MachO/Arch/X86_64.cpp
@@ -39,6 +39,9 @@ struct X86_64 : TargetInfo {
void relaxGotLoad(uint8_t *loc, uint8_t type) const override;
const RelocAttrs &getRelocAttrs(uint8_t type) const override;
uint64_t getPageSize() const override { return 4 * 1024; }
+
+ void handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const override;
};
} // namespace
@@ -199,3 +202,23 @@ TargetInfo *macho::createX86_64TargetInfo() {
static X86_64 t;
return &t;
}
+
+void X86_64::handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const {
+ assert(r.type == X86_64_RELOC_BRANCH);
+
+ if (config->outputType == MH_OBJECT)
+ return;
+
+ if (sym->getName().startswith("___dtrace_probe")) {
+ // change call site to a NOP
+ loc[-1] = 0x90;
+ write32le(loc, 0x00401F0F);
+ } else if (sym->getName().startswith("___dtrace_isenabled")) {
+ // change call site to a clear eax
+ loc[-1] = 0x33;
+ write32le(loc, 0x909090C0);
+ } else {
+ error("Unrecognized dtrace symbol prefix: " + toString(*sym));
+ }
+}
diff --git a/lld/MachO/InputSection.cpp b/lld/MachO/InputSection.cpp
index 25eb878736d9f..df312525df610 100644
--- a/lld/MachO/InputSection.cpp
+++ b/lld/MachO/InputSection.cpp
@@ -201,6 +201,12 @@ void ConcatInputSection::writeTo(uint8_t *buf) {
if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&
!referentSym->isInGot())
target->relaxGotLoad(loc, r.type);
+ // For dtrace symbols, do not handle them as normal undefined symbols
+ if (referentSym->getName().startswith("___dtrace_")) {
+ // Change dtrace call site to pre-defined instructions
+ target->handleDtraceReloc(referentSym, r, loc);
+ continue;
+ }
referentVA = resolveSymbolVA(referentSym, r.type) + r.addend;
if (isThreadLocalVariables(getFlags())) {
diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
index d309f66c119fb..7bda1d13069fa 100644
--- a/lld/MachO/SymbolTable.cpp
+++ b/lld/MachO/SymbolTable.cpp
@@ -332,6 +332,10 @@ static bool recoverFromUndefinedSymbol(const Undefined &sym) {
return true;
}
+ // Leave dtrace symbols, since we will handle them when we do the relocation
+ if (name.startswith("___dtrace_"))
+ return true;
+
// Handle -U.
if (config->explicitDynamicLookups.count(sym.getName())) {
symtab->addDynamicLookup(sym.getName());
diff --git a/lld/MachO/Target.h b/lld/MachO/Target.h
index 09ff3c5639ea6..597502275deed 100644
--- a/lld/MachO/Target.h
+++ b/lld/MachO/Target.h
@@ -79,6 +79,15 @@ class TargetInfo {
bool usesThunks() const { return thunkSize > 0; }
+ // For now, handleDtraceReloc only implements -no_dtrace_dof, and ensures
+ // that the linking would not fail even when there are user-provided dtrace
+ // symbols. However, unlike ld64, lld currently does not emit __dof sections.
+ virtual void handleDtraceReloc(const Symbol *sym, const Reloc &r,
+ uint8_t *loc) const {
+ llvm_unreachable("Unsupported architecture for dtrace symbols");
+ }
+
+
virtual void applyOptimizationHints(uint8_t *buf, const ConcatInputSection *,
llvm::ArrayRef<uint64_t>) const {};
diff --git a/lld/test/MachO/arm-dtrace.s b/lld/test/MachO/arm-dtrace.s
new file mode 100644
index 0000000000000..4d69d56542c51
--- /dev/null
+++ b/lld/test/MachO/arm-dtrace.s
@@ -0,0 +1,45 @@
+# REQUIRES: arm
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=armv4t-apple-darwin %t/armv4t-dtrace.s -o %t/armv4t-dtrace.o
+# RUN: %lld -arch armv4t -o %t/armv4t-dtrace %t/armv4t-dtrace.o
+
+## If references of dtrace symbols are handled by lld, their relocation should be replaced with the following instructions
+# RUN: llvm-objdump --macho -D %t/armv4t-dtrace | FileCheck %s --check-prefix=CHECK-armv4t
+
+# CHECK-armv4t: 00 00 20 e0 eor r0, r0, r0
+
+# CHECK-armv4t: 00 00 a0 e1 mov r0, r0
+
+# RUN: llvm-mc -filetype=obj -triple=thumbv7-apple-darwin %t/armv7-dtrace.s -o %t/armv7-dtrace.o
+# RUN: %lld -arch armv7 -o %t/armv7-dtrace %t/armv7-dtrace.o
+
+## If references of dtrace symbols are handled by lld, their relocation should be replaced with the following instructions
+# RUN: llvm-objdump --macho -D %t/armv7-dtrace | FileCheck %s --check-prefix=CHECK-armv7
+
+# CHECK-armv7: 40 40 eors r0, r0
+# CHECK-armv7-NEXT: c0 46 mov r8, r8
+
+# CHECK-armv7: c0 46 mov r8, r8
+# CHECK-armv7-NEXT: c0 46 mov r8, r8
+
+;--- armv4t-dtrace.s
+ .globl _main
+_main:
+ bl ___dtrace_isenabled$Foo$added$v1
+ .reference ___dtrace_typedefs$Foo$v2
+ bl ___dtrace_probe$Foo$added$v1$696e74
+ .reference ___dtrace_stability$Foo$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
+
+.subsections_via_symbols
+
+;--- armv7-dtrace.s
+ .globl _main
+ .thumb_func _main
+_main:
+ bl ___dtrace_isenabled$Foo$added$v1
+ .reference ___dtrace_typedefs$Foo$v2
+ bl ___dtrace_probe$Foo$added$v1$696e74
+ .reference ___dtrace_stability$Foo$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
+
+.subsections_via_symbols
diff --git a/lld/test/MachO/arm64-32-dtrace.s b/lld/test/MachO/arm64-32-dtrace.s
new file mode 100644
index 0000000000000..23e45f63085ea
--- /dev/null
+++ b/lld/test/MachO/arm64-32-dtrace.s
@@ -0,0 +1,23 @@
+# REQUIRES: aarch64
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=arm64_32-apple-darwin %t/arm64-32-dtrace.s -o %t/arm64-32-dtrace.o
+# RUN: %lld -arch arm64_32 -o %t/arm64-32-dtrace %t/arm64-32-dtrace.o
+
+## If references of dtrace symbols are handled by lld, their relocation should be replaced with the following instructions
+# RUN: llvm-objdump --macho -D %t/arm64-32-dtrace | FileCheck %s --check-prefix=CHECK
+
+# CHECK: 00 00 80 d2 mov x0, #0
+
+# CHECK: 1f 20 03 d5 nop
+
+#--- arm64-32-dtrace.s
+ .globl _main
+_main:
+ bl ___dtrace_isenabled$Foo$added$v1
+ .reference ___dtrace_typedefs$Foo$v2
+ bl ___dtrace_probe$Foo$added$v1$696e74
+ .reference ___dtrace_stability$Foo$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
+ ret
+
+.subsections_via_symbols
diff --git a/lld/test/MachO/arm64-dtrace.s b/lld/test/MachO/arm64-dtrace.s
new file mode 100644
index 0000000000000..36854195e3142
--- /dev/null
+++ b/lld/test/MachO/arm64-dtrace.s
@@ -0,0 +1,23 @@
+# REQUIRES: aarch64
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %t/arm64-dtrace.s -o %t/arm64-dtrace.o
+# RUN: %lld -arch arm64 -o %t/arm64-dtrace %t/arm64-dtrace.o
+
+## If references of dtrace symbols are handled by lld, their relocation should be replaced with the following instructions
+# RUN: llvm-objdump --macho -D %t/arm64-dtrace | FileCheck %s --check-prefix=CHECK
+
+# CHECK: 00 00 80 d2 mov x0, #0
+
+# CHECK: 1f 20 03 d5 nop
+
+#--- arm64-dtrace.s
+ .globl _main
+_main:
+ bl ___dtrace_isenabled$Foo$added$v1
+ .reference ___dtrace_typedefs$Foo$v2
+ bl ___dtrace_probe$Foo$added$v1$696e74
+ .reference ___dtrace_stability$Foo$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
+ ret
+
+.subsections_via_symbols
diff --git a/lld/test/MachO/x86_64-dtrace.s b/lld/test/MachO/x86_64-dtrace.s
new file mode 100644
index 0000000000000..7caedca3efd15
--- /dev/null
+++ b/lld/test/MachO/x86_64-dtrace.s
@@ -0,0 +1,27 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/x86_64-dtrace.s -o %t/x86_64-dtrace.o
+# RUN: %lld -arch x86_64 -o %t/x86_64-dtrace %t/x86_64-dtrace.o
+
+## If references of dtrace symbols are handled by lld, their relocation should be replaced with the following instructions
+# RUN: llvm-objdump --macho -D %t/x86_64-dtrace | FileCheck %s --check-prefix=CHECK
+
+# CHECK: 33 c0 xorl %eax, %eax
+# CHECK-NEXT: 90 nop
+# CHECK-NEXT: 90 nop
+# CHECK-NEXT: 90 nop
+
+# CHECK: 90 nop
+# CHECK-NEXT: 0f 1f 40 00 nopl (%rax)
+
+#--- x86_64-dtrace.s
+ .globl _main
+_main:
+ callq ___dtrace_isenabled$Foo$added$v1
+ .reference ___dtrace_typedefs$Foo$v2
+ callq ___dtrace_probe$Foo$added$v1$696e74
+ .reference ___dtrace_stability$Foo$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
+ retq
+
+.subsections_via_symbols
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