http://sourceware.org/bugzilla/show_bug.cgi?id=15167
Bug #: 15167 Summary: ld merges gnu_unique def and normal ref into normal symbol Product: binutils Version: 2.24 (HEAD) Status: NEW Severity: normal Priority: P2 Component: ld AssignedTo: unassig...@sourceware.org ReportedBy: m...@suse.de Classification: Unclassified This came up over at http://gcc.gnu.org/ml/gcc/2013-02/msg00227.html describing a strange mismatch between two symbols that are unique, but in the shared object one is normal and the other is unique. I traced this back to an ordering problem in ld at http://gcc.gnu.org/ml/gcc/2013-02/msg00239.html . The binutils involved there are 2.21.1, but current upstream still exhibits the issue. I made a minimal testcase with two asm files: % cat unique1.s .file "unique.cc" .weak _ZN1SIiE1iE .section .bss._ZN1SIiE1iE,"awG",@nobits,_ZN1SIiE1iE,comdat .align 4 .type _ZN1SIiE1iE, @gnu_unique_object .size _ZN1SIiE1iE, 4 _ZN1SIiE1iE: .zero 4 .ident "GCC: (GNU) 4.6.1 20110505 (prerelease)" .section .note.GNU-stack,"",@progbits % cat unique2.s .file "unique.cc" .text .align 2 .globl _ZN1SIiE3getEv .type _ZN1SIiE3getEv, @function _ZN1SIiE3getEv: .LFB0: .cfi_startproc pushq %rbp .cfi_def_cfa_offset 16 .cfi_offset 6, -16 movq %rsp, %rbp .cfi_def_cfa_register 6 movq %rdi, -8(%rbp) movq _ZN1SIiE1iE@GOTPCREL(%rip), %rax movl (%rax), %eax popq %rbp .cfi_def_cfa 7, 8 ret .cfi_endproc .LFE0: .size _ZN1SIiE3getEv, .-_ZN1SIiE3getEv .ident "GCC: (GNU) 4.6.1 20110505 (prerelease)" .section .note.GNU-stack,"",@progbits % gcc -c unique1.s unique2.s % ./ld/ld-new -shared -o unique-ok.so unique2.o unique1.o % ./ld/ld-new -shared -o unique-bad.so unique1.o unique2.o % nm -D unique-bad.so | grep _ZN1SIiE1iE 0000000000200398 B _ZN1SIiE1iE % nm -D unique-ok.so | grep _ZN1SIiE1iE 0000000000200398 u _ZN1SIiE1iE In difference is that for unique-ok.so the reference to _ZN1SIiE1iE comes first (in unique2.o), then the definition (in unique1.o), and that results correctly in a global unique symbol exported from the DSO. For unique-bad.so the definition comes first, and the uniqueness seems to get lost when the normal reference is seen, so a normal global (not even weak) symbol is now exported from the DSO. This can (and as the thread at gcc@ shows actually does) lead to problems when the system relies on some symbols to be indeed globally unique. The empty_rep static member of libstdc++'s string<> and wstring<> templates is one example. As said, this is broken in at least 2.21.1 and in current trunk. FWIW, the C++ source I used to initially generate the above asms is: template <typename T> struct S { static T i; T get(); }; template <typename T> T S<T>::i; template <> int S<int>::get() { return i; } compiled with -fPIC, and then split the .s into two by hand. -- Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug. _______________________________________________ bug-binutils mailing list bug-binutils@gnu.org https://lists.gnu.org/mailman/listinfo/bug-binutils