[LLVMbugs] [Bug 9352] New: [MC assembler] relocations for weak symbols not generated

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9352

           Summary: [MC assembler] relocations for weak symbols not
                    generated
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: dimitry at andric.com
                CC: llvmbugs at cs.uiuc.edu


Clang's integrated assembler does not always generate external
relocations for weak symbols, even when that is required.

Test case:

        .weak   foo
        .equ    foo, foo_stub

        .text
foo_stub:
        ret

bar:
        call    foo
        ret

Here, the "call foo" should be resolved at link time, so the assembler
should put in a relocation.  GNU as assembles this to:

0000000000000000 <foo>:
   0:   c3                      retq

0000000000000001 <bar>:
   1:   e8 00 00 00 00          callq  6 <bar+0x5>
   6:   c3                      retq

and it creates the following relocation for the call:

relocation with addend (.rela.text):

entry: 0
        r_offset: 0x2
        r_info: 2
        r_addend: -4

In contrast, clang r126742 integrated-as produces:

0000000000000000 <foo>:
   0:   c3                      retq

0000000000000001 <bar>:
   1:   e8 fa ff ff ff          callq  0 <foo>
   6:   c3                      retq

so does not create any relocation; it short-circuits the "call foo"
directly.

On FreeBSD, this breaks our malloc very, very badly. :)

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