[lld] r266121 - ELF: Give automatically generated __start_* and __stop_* symbols hidden visibility.
Peter Collingbourne via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 12 13:41:42 PDT 2016
Author: pcc
Date: Tue Apr 12 15:41:42 2016
New Revision: 266121
URL: http://llvm.org/viewvc/llvm-project?rev=266121&view=rev
Log:
ELF: Give automatically generated __start_* and __stop_* symbols hidden visibility.
These symbols describe a property of a linkage unit, so it seems reasonable
to limit their visibility to the linkage unit. Furthermore the use cases I
am aware of do not require more than hidden visibility.
This is a departure from the behavior of the bfd and gold linkers. However,
it is unclear that the decision to give these symbols default visibility
in those linkers was made deliberately. The __start_*/__stop_* feature
was added to the bfd linker in 1994 [1], while the visibility feature was
added about five years later [2], so it may have been that the visibility
of these symbols was not considered. The feature was implemented in gold
[3] in the same way; the behavior may have simply been copied from bfd.
The only related discussion I could find on the binutils mailing list [4]
was a user issue which would most likely not have occurred if the symbols
had hidden visibility.
[1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=5efddb2e7c3229b569a862205f61d42860af678b
[2] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=0fc731e447cd01e7fc35197b487ff0e4fd25afca
[3] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=bfd58944a64b0997a310b95fbe0423338961e71c
[4] https://sourceware.org/ml/binutils/2014-05/msg00011.html
Differential Revision: http://reviews.llvm.org/D19024
Modified:
lld/trunk/ELF/Writer.cpp
lld/trunk/test/ELF/startstop-shared.s
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=266121&r1=266120&r2=266121&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Tue Apr 12 15:41:42 2016
@@ -1261,11 +1261,11 @@ void Writer<ELFT>::addStartStopSymbols(O
StringRef Stop = Saver.save("__stop_" + S);
if (SymbolBody *B = Symtab.find(Start))
if (B->isUndefined())
- Symtab.addSynthetic(Start, *Sec, 0, STV_DEFAULT);
+ Symtab.addSynthetic(Start, *Sec, 0, STV_HIDDEN);
if (SymbolBody *B = Symtab.find(Stop))
if (B->isUndefined())
Symtab.addSynthetic(Stop, *Sec, DefinedSynthetic<ELFT>::SectionEnd,
- STV_DEFAULT);
+ STV_HIDDEN);
}
template <class ELFT> static bool needsPtLoad(OutputSectionBase<ELFT> *Sec) {
Modified: lld/trunk/test/ELF/startstop-shared.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/startstop-shared.s?rev=266121&r1=266120&r2=266121&view=diff
==============================================================================
--- lld/trunk/test/ELF/startstop-shared.s (original)
+++ lld/trunk/test/ELF/startstop-shared.s Tue Apr 12 15:41:42 2016
@@ -5,21 +5,21 @@
.quad __start_foo
.section foo,"a"
-// By default the symbol is visible and we need a dynamic reloc.
-// CHECK: R_X86_64_64 __start_foo 0x0
+// By default the symbol is hidden.
+// CHECK: R_X86_64_RELATIVE - 0x[[ADDR1:.*]]
.hidden __start_bar
.quad __start_bar
.section bar,"a"
-// Test that we are able to hide the symbol.
-// CHECK: R_X86_64_RELATIVE - 0x[[ADDR:.*]]
+// References do not affect the visibility.
+// CHECK: R_X86_64_RELATIVE - 0x[[ADDR2:.*]]
// CHECK: Name: __start_bar
-// CHECK-NEXT: Value: 0x[[ADDR]]
+// CHECK-NEXT: Value: 0x[[ADDR2]]
// CHECK-NEXT: Size:
// CHECK-NEXT: Binding: Local
// CHECK: Name: __start_foo
-// CHECK-NEXT: Value:
+// CHECK-NEXT: Value: 0x[[ADDR1]]
// CHECK-NEXT: Size:
-// CHECK-NEXT: Binding: Global
+// CHECK-NEXT: Binding: Local
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