[LLVMbugs] [Bug 21288] New: mis-compile of TLS+alias (extracted from glibc's errno.c)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21288

            Bug ID: 21288
           Summary: mis-compile of TLS+alias (extracted from glibc's
                    errno.c)
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: david.majnemer at gmail.com
          Reporter: kcc at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

test case (extracted from glibc's csu/errno.c): 

__thread int TL_WITH_ALIAS;
extern __thread int __libc_errno __attribute__ ((alias ("TL_WITH_ALIAS")));

gcc produces tbss. 
clang produces bss.     (tested with clang r219701 on x86_64 linux)

Chandler says to show this to David Majnemer

% for c in gcc clang; do $c -S p.c  -o -; echo =======================; done 
    .file    "p.c"
    .globl    TL_WITH_ALIAS
    .section    .tbss,"awT", at nobits
    .align 4
    .type    TL_WITH_ALIAS, @object
    .size    TL_WITH_ALIAS, 4
TL_WITH_ALIAS:
    .zero    4
    .globl    __libc_errno
    .set    __libc_errno,TL_WITH_ALIAS
    .ident    "GCC: (Ubuntu 4.8.2-19ubuntu1) 4.8.2"
    .section    .note.GNU-stack,"", at progbits
=======================
    .text
    .file    "p.c"
    .type    TL_WITH_ALIAS, at object   # @TL_WITH_ALIAS
    .bss
    .globl    TL_WITH_ALIAS
    .align    4
TL_WITH_ALIAS:
    .long    0                       # 0x0
    .size    TL_WITH_ALIAS, 4


    .globl    __libc_errno
__libc_errno = TL_WITH_ALIAS
    .ident    "clang version 3.6.0 (219701)"
    .section    ".note.GNU-stack","", at progbits
=======================

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