[llvm] 7a66a26 - [llvm-objcopy,ELF] --discard-locals/--discard-all: allow and keep symbols referenced by relocations
via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 11 21:26:17 PDT 2025
Author: Fangrui Song
Date: 2025-03-11T21:26:13-07:00
New Revision: 7a66a26658f40d00ad4c298260d9c3b8f91e1368
URL: https://github.com/llvm/llvm-project/commit/7a66a26658f40d00ad4c298260d9c3b8f91e1368
DIFF: https://github.com/llvm/llvm-project/commit/7a66a26658f40d00ad4c298260d9c3b8f91e1368.diff
LOG: [llvm-objcopy,ELF] --discard-locals/--discard-all: allow and keep symbols referenced by relocations
In GNU objcopy, symbols referenced by relocations are retained. Our COFF
(https://reviews.llvm.org/D56480) and Mach-O
(https://reviews.llvm.org/D75104) ports port the behavior, but the ELF
port doesn't.
This PR implements the behavior for ELF.
Close #47468 (tcl has a use case that requires `strip -x tclStubLib.o`
to strip local symbols not referenced by relocations.)
Pull Request: https://github.com/llvm/llvm-project/pull/130704
Added:
Modified:
llvm/docs/CommandGuide/llvm-objcopy.rst
llvm/docs/ReleaseNotes.md
llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp
llvm/test/tools/llvm-objcopy/ELF/discard-all.test
llvm/test/tools/llvm-objcopy/ELF/discard-locals.test
Removed:
llvm/test/tools/llvm-objcopy/ELF/discard-locals-rel.test
################################################################################
diff --git a/llvm/docs/CommandGuide/llvm-objcopy.rst b/llvm/docs/CommandGuide/llvm-objcopy.rst
index 8dc1357635e1b..96f3247780b3b 100644
--- a/llvm/docs/CommandGuide/llvm-objcopy.rst
+++ b/llvm/docs/CommandGuide/llvm-objcopy.rst
@@ -57,9 +57,10 @@ multiple file formats.
.. option:: --discard-all, -x
- Remove most local symbols from the output. Different file formats may limit
- this to a subset of the local symbols. For example, file and section symbols in
- ELF objects will not be discarded. Additionally, remove all debug sections.
+ Remove most local symbols not referenced by relocations from the output.
+ Different file formats may limit this to a subset of the local symbols. For
+ example, file and section symbols in ELF objects will not be discarded.
+ Additionally, remove all debug sections.
.. option:: --dump-section <section>=<file>
@@ -386,7 +387,7 @@ them.
.. option:: --discard-locals, -X
- Remove local symbols starting with ".L" from the output.
+ Remove local symbols starting with ".L" not referenced by relocations from the output.
.. option:: --extract-dwo
diff --git a/llvm/docs/ReleaseNotes.md b/llvm/docs/ReleaseNotes.md
index d7a80ae93aa34..3d608c636a8f6 100644
--- a/llvm/docs/ReleaseNotes.md
+++ b/llvm/docs/ReleaseNotes.md
@@ -160,6 +160,7 @@ Changes to the LLVM tools
* llvm-objcopy now supports the `--update-section` flag for intermediate Mach-O object files.
* llvm-strip now supports continuing to process files on encountering an error.
+* In llvm-objcopy's ELF port, `--discard-locals` and `--discard-all` now allow and preserve symbols referenced by relocations.
Changes to LLDB
---------------------------------
diff --git a/llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp b/llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp
index 1a31bfa2e0db3..5a785d7afd1e4 100644
--- a/llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp
+++ b/llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp
@@ -364,7 +364,7 @@ static Error updateAndRemoveSymbols(const CommonConfig &Config,
// (like GroupSection or RelocationSection). This way, we know which
// symbols are still 'needed' and which are not.
if (Config.StripUnneeded || !Config.UnneededSymbolsToRemove.empty() ||
- !Config.OnlySection.empty()) {
+ !Config.OnlySection.empty() || Config.DiscardMode != DiscardType::None) {
for (SectionBase &Sec : Obj.sections())
Sec.markSymbols();
}
@@ -386,22 +386,23 @@ static Error updateAndRemoveSymbols(const CommonConfig &Config,
if (Config.StripDebug && Sym.Type == STT_FILE)
return true;
- if ((Config.DiscardMode == DiscardType::All ||
- (Config.DiscardMode == DiscardType::Locals &&
- StringRef(Sym.Name).starts_with(".L"))) &&
- Sym.Binding == STB_LOCAL && Sym.getShndx() != SHN_UNDEF &&
- Sym.Type != STT_FILE && Sym.Type != STT_SECTION)
- return true;
-
if ((Config.StripUnneeded ||
Config.UnneededSymbolsToRemove.matches(Sym.Name)) &&
(!Obj.isRelocatable() || isUnneededSymbol(Sym)))
return true;
- // We want to remove undefined symbols if all references have been stripped.
- if (!Config.OnlySection.empty() && !Sym.Referenced &&
- Sym.getShndx() == SHN_UNDEF)
- return true;
+ if (!Sym.Referenced) {
+ if ((Config.DiscardMode == DiscardType::All ||
+ (Config.DiscardMode == DiscardType::Locals &&
+ StringRef(Sym.Name).starts_with(".L"))) &&
+ Sym.Binding == STB_LOCAL && Sym.getShndx() != SHN_UNDEF &&
+ Sym.Type != STT_FILE && Sym.Type != STT_SECTION)
+ return true;
+ // We want to remove undefined symbols if all references have been
+ // stripped.
+ if (!Config.OnlySection.empty() && Sym.getShndx() == SHN_UNDEF)
+ return true;
+ }
return false;
};
diff --git a/llvm/test/tools/llvm-objcopy/ELF/discard-all.test b/llvm/test/tools/llvm-objcopy/ELF/discard-all.test
index 50cad3ae9f533..ce65026715f71 100644
--- a/llvm/test/tools/llvm-objcopy/ELF/discard-all.test
+++ b/llvm/test/tools/llvm-objcopy/ELF/discard-all.test
@@ -32,6 +32,14 @@ Sections:
Address: 0x1000
AddressAlign: 0x0000000000000010
Size: 64
+ - Name: .rela.text
+ Type: SHT_RELA
+ Link: .symtab
+ Info: .text
+ Relocations:
+ - Offset: 0
+ Symbol: Referenced
+ Type: R_X86_64_PC32
Symbols:
- Name: Local
Type: STT_FUNC
@@ -49,6 +57,8 @@ Symbols:
Section: .text
Value: 0x1010
Binding: STB_GLOBAL
+ - Name: Referenced
+ Section: .text
- Name: Weak
Type: STT_FUNC
Size: 8
@@ -85,6 +95,15 @@ Symbols:
#CHECK-NEXT: Section: Undefined
#CHECK-NEXT: }
#CHECK-NEXT: Symbol {
+#CHECK-NEXT: Name: Referenced
+#CHECK-NEXT: Value: 0x0
+#CHECK-NEXT: Size: 0
+#CHECK-NEXT: Binding: Local
+#CHECK-NEXT: Type: None
+#CHECK-NEXT: Other: 0
+#CHECK-NEXT: Section: .text
+#CHECK-NEXT: }
+#CHECK-NEXT: Symbol {
#CHECK-NEXT: Name: Global
#CHECK-NEXT: Value: 0x1010
#CHECK-NEXT: Size: 8
diff --git a/llvm/test/tools/llvm-objcopy/ELF/discard-locals-rel.test b/llvm/test/tools/llvm-objcopy/ELF/discard-locals-rel.test
deleted file mode 100644
index 00bb8fcf18205..0000000000000
--- a/llvm/test/tools/llvm-objcopy/ELF/discard-locals-rel.test
+++ /dev/null
@@ -1,26 +0,0 @@
-# RUN: yaml2obj %s -o %t
-# RUN: not llvm-objcopy --discard-locals %t %t2 2>&1 | FileCheck %s -DFILE=%t
-
-!ELF
-FileHeader:
- Class: ELFCLASS64
- Data: ELFDATA2LSB
- Type: ET_REL
- Machine: EM_X86_64
-Sections:
- - Name: .text
- Type: SHT_PROGBITS
- - Name: .rel.text
- Type: SHT_REL
- Link: .symtab
- Info: .text
- Relocations:
- - Offset: 0x1000
- Symbol: .L.rel
- Type: R_X86_64_PC32
-Symbols:
- - Name: .L.rel
- Type: STT_FUNC
- Section: .text
-
-# CHECK: error: '[[FILE]]': not stripping symbol '.L.rel' because it is named in a relocation
diff --git a/llvm/test/tools/llvm-objcopy/ELF/discard-locals.test b/llvm/test/tools/llvm-objcopy/ELF/discard-locals.test
index 4aba1cd1c782a..c1fe0f2b02b6e 100644
--- a/llvm/test/tools/llvm-objcopy/ELF/discard-locals.test
+++ b/llvm/test/tools/llvm-objcopy/ELF/discard-locals.test
@@ -29,6 +29,14 @@ FileHeader:
Sections:
- Name: .text
Type: SHT_PROGBITS
+ - Name: .rela.text
+ Type: SHT_RELA
+ Link: .symtab
+ Info: .text
+ Relocations:
+ - Offset: 0
+ Symbol: .L.referenced
+ Type: R_X86_64_PC32
- Name: .LLVM.Custom.Section
Type: SHT_PROGBITS
Symbols:
@@ -48,6 +56,8 @@ Symbols:
- Name: .L.undefined
- Name: .L.abs
Index: SHN_ABS
+ - Name: .L.referenced
+ Section: .text
- Name: .L.Global
Type: STT_FUNC
Section: .text
@@ -109,6 +119,15 @@ Symbols:
# CHECK-NEXT: Section: Undefined
# CHECK-NEXT: }
# CHECK-NEXT: Symbol {
+# CHECK-NEXT: Name: .L.referenced
+# CHECK-NEXT: Value:
+# CHECK-NEXT: Size:
+# CHECK-NEXT: Binding: Local
+# CHECK-NEXT: Type: None
+# CHECK-NEXT: Other:
+# CHECK-NEXT: Section: .text
+# CHECK-NEXT: }
+# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: .L.Global
# CHECK-NEXT: Value:
# CHECK-NEXT: Size:
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