[LLVMbugs] [Bug 18725] New: Struct not passed correctly in vararg

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Feb 4 07:06:57 PST 2014


            Bug ID: 18725
           Summary: Struct not passed correctly in vararg
           Product: clang
           Version: trunk
          Hardware: PC
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ishiura-compiler at ml.kwansei.ac.jp
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Clang 3.5 (based on LLVM 3.5svn) for x86_64 target miscompiles the following

    $ cat error.c

    #include <stdarg.h>

    struct S { float m0[2]; int m1; };

    void func(int x, ... )
        va_list ap;
        va_start(ap, x);
        struct S y = va_arg(ap, struct S);

        if( y.m1 != 1 ) { __builtin_abort(); }

    int main(void)
        int x;
        struct S s = {{1,1},1};
        func(x, s);

        return 0;

    $ clang error.c

    $ ./a.out
    Abort trap: 6

The value of y.m1 was 1065353216 instead of 1.
There was no problem with an i686 target.

    $ clang -v
    clang version 3.5 (trunk 200763)
    Target: x86_64-apple-darwin13.0.0
    Thread model: posix

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