[lld] 4e572db - [lld/mac] Mark private externs with GOT relocs as LOCAL in indirect symbtab
Nico Weber via llvm-commits
llvm-commits at lists.llvm.org
Fri Oct 15 10:24:53 PDT 2021
Author: Nico Weber
Date: 2021-10-15T13:24:47-04:00
New Revision: 4e572db0c2ec4e96f8ddfade7384e8ee8ad97384
URL: https://github.com/llvm/llvm-project/commit/4e572db0c2ec4e96f8ddfade7384e8ee8ad97384
DIFF: https://github.com/llvm/llvm-project/commit/4e572db0c2ec4e96f8ddfade7384e8ee8ad97384.diff
LOG: [lld/mac] Mark private externs with GOT relocs as LOCAL in indirect symbtab
prepareSymbolRelocation() in Writer.cpp adds both symbols that need binding and
symbols relocated with a pointer relocation to the got.
Pointer relocations are emitted for non-movq GOTPCREL(%rip) loads. (movqs
become GOT_LOADs so that the linker knows they can be relaxed to leaqs, while
others, such as addq, become just GOT -- a pointer relocation -- since they
can't be relaxed in that way).
For example, this C file produces a private_extern GOT relocation when
compiled with -O2 with clang:
extern const char kString[];
const char* g(int a) { return kString + a; }
Linkers need to put pointer-relocated symbols into the GOT, but ld64 marks them
as LOCAL in the indirect symbol table. This matters, since `strip -x` looks at
the indirect symbol table when deciding what to strip.
The indirect symtab emitting code was assuming that only symbols that need
binding are in the GOT, but pointer relocations where there too. Hence, the
code needs to explicitly check if a symbol is a private extern.
Fixes https://crbug.com/1242638, which has some more information in comments 14
and 15. With this patch, the output of `nm -U` on Chromium Framework after
stripping now contains just two symbols when using lld, just like with ld64.
Differential Revision: https://reviews.llvm.org/D111852
Added:
Modified:
lld/MachO/SyntheticSections.cpp
lld/test/MachO/compact-unwind-both-local-and-dylib-personality.s
lld/test/MachO/indirect-symtab.s
Removed:
################################################################################
diff --git a/lld/MachO/SyntheticSections.cpp b/lld/MachO/SyntheticSections.cpp
index 61fbf7487cc0d..81f9224a1d2ca 100644
--- a/lld/MachO/SyntheticSections.cpp
+++ b/lld/MachO/SyntheticSections.cpp
@@ -1104,8 +1104,12 @@ void IndirectSymtabSection::finalizeContents() {
}
static uint32_t indirectValue(const Symbol *sym) {
- return sym->symtabIndex != UINT32_MAX ? sym->symtabIndex
- : INDIRECT_SYMBOL_LOCAL;
+ if (sym->symtabIndex == UINT32_MAX)
+ return INDIRECT_SYMBOL_LOCAL;
+ if (auto *defined = dyn_cast<Defined>(sym))
+ if (defined->privateExtern)
+ return INDIRECT_SYMBOL_LOCAL;
+ return sym->symtabIndex;
}
void IndirectSymtabSection::writeTo(uint8_t *buf) const {
diff --git a/lld/test/MachO/compact-unwind-both-local-and-dylib-personality.s b/lld/test/MachO/compact-unwind-both-local-and-dylib-personality.s
index a4ef172d7f7c0..933fcd6939166 100644
--- a/lld/test/MachO/compact-unwind-both-local-and-dylib-personality.s
+++ b/lld/test/MachO/compact-unwind-both-local-and-dylib-personality.s
@@ -33,12 +33,13 @@
# A: Indirect symbols for (__DATA_CONST,__got)
# A-NEXT: address index name
# A-DAG: 0x[[#%x,GXX_PERSONALITY_LO:]] [[#]] ___gxx_personality_v0
-# A-DAG: 0x[[#%x,GXX_PERSONALITY_HI:]] [[#]] ___gxx_personality_v0
+# A-DAG: 0x[[#%x,GXX_PERSONALITY_HI:]] [[#]] ___gxx_personality_v0
# A-DAG: 0x[[#%x,PERSONALITY_1:]] LOCAL
# A-DAG: 0x[[#%x,PERSONALITY_2:]] LOCAL
# BC: Indirect symbols for (__DATA_CONST,__got)
# BC-NEXT: address index name
+# BC-DAG: 0x[[#%x,GXX_PERSONALITY_HI:]] LOCAL
# BC-DAG: 0x[[#%x,GXX_PERSONALITY_LO:]] LOCAL
# BC-DAG: 0x[[#%x,PERSONALITY_1:]] LOCAL
# BC-DAG: 0x[[#%x,PERSONALITY_2:]] LOCAL
diff --git a/lld/test/MachO/indirect-symtab.s b/lld/test/MachO/indirect-symtab.s
index 9c64735e5487e..52849ccb87455 100644
--- a/lld/test/MachO/indirect-symtab.s
+++ b/lld/test/MachO/indirect-symtab.s
@@ -2,8 +2,9 @@
# RUN: rm -rf %t; split-file %s %t
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/libfoo.s -o %t/libfoo.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/bar.s -o %t/bar.o
# RUN: %lld -dylib %t/libfoo.o -o %t/libfoo.dylib -lSystem
-# RUN: %lld %t/test.o %t/libfoo.dylib -o %t/test -lSystem
+# RUN: %lld %t/test.o %t/bar.o %t/libfoo.dylib -o %t/test -lSystem
# RUN: llvm-objdump --macho -d --no-show-raw-insn --indirect-symbols %t/test | FileCheck %s
# RUN: llvm-otool -l %t/test | FileCheck --check-prefix=DYSYMTAB %s
@@ -11,6 +12,8 @@
# CHECK-NEXT: _main:
# CHECK-NEXT: movq {{.*}}(%rip), %rax ## literal pool symbol address: _foo
# CHECK-NEXT: movq {{.*}}(%rip), %rax ## literal pool symbol address: _bar
+# CHECK-NEXT: leaq _baz(%rip), %rax
+# CHECK-NEXT: addq {{.*}}(%rip), %rax
# CHECK-NEXT: movq {{.*}}(%rip), %rax ## literal pool symbol address: _foo_tlv
# CHECK-NEXT: movq {{.*}}(%rip), %rax ## literal pool symbol address: _bar_tlv
# CHECK-NEXT: callq {{.*}} ## symbol stub for: _foo_fn
@@ -21,8 +24,9 @@
# CHECK-NEXT: address index name
# CHECK-NEXT: _bar_fn
# CHECK-NEXT: _foo_fn
-# CHECK-NEXT: Indirect symbols for (__DATA_CONST,__got) 3 entries
+# CHECK-NEXT: Indirect symbols for (__DATA_CONST,__got) 4 entries
# CHECK-NEXT: address index name
+# CHECK-NEXT: LOCAL
# CHECK-NEXT: _bar
# CHECK-NEXT: _foo
# CHECK-NEXT: _stub_binder
@@ -35,7 +39,7 @@
# CHECK-NEXT: _bar_tlv
# CHECK-NEXT: _foo_tlv
-# DYSYMTAB: nindirectsyms 9
+# DYSYMTAB: nindirectsyms 10
#--- libfoo.s
@@ -56,8 +60,19 @@ _bar_tlv:
_main:
movq _foo at GOTPCREL(%rip), %rax
movq _bar at GOTPCREL(%rip), %rax
+ movq _baz at GOTPCREL(%rip), %rax
+ addq _quux at GOTPCREL(%rip), %rax
mov _foo_tlv at TLVP(%rip), %rax
mov _bar_tlv at TLVP(%rip), %rax
callq _foo_fn
callq _bar_fn
ret
+
+#--- bar.s
+.data
+.globl _baz,_quux
+.private_extern _baz,_quux
+_baz:
+.asciz "baz"
+_quux:
+.asciz "quux"
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