[llvm-bugs] [Bug 27663] New: __builtin_va_arg stack-walk short

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27663

            Bug ID: 27663
           Summary: __builtin_va_arg stack-walk short
           Product: clang
           Version: 3.8
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: zenith432 at users.sourceforge.net
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

I've marked this as clang 3.8, but code was compiled on Apple's Xcode 7.3.1.
Sample code
================ va_sum.c
int va_sum(unsigned int count, ...)
{
    int sum = 0;
    __builtin_ms_va_list ap;

    __builtin_ms_va_start(ap, count);
    while (count) {
        sum += __builtin_va_arg(ap, int);
        --count;
    }
    __builtin_ms_va_end(ap);
    return sum;
}
==================

Compiled with
clang -S -Os -fno-unwind-tables -target x86_64-pc-win32-macho va_sum.c

generates this code
================ va_sum.s
    .section    __TEXT,__text,regular,pure_instructions
    .globl    _va_sum
_va_sum:                                ## @va_sum
## BB#0:
    pushq    %rax
    movq    %r9, 40(%rsp)
    movq    %r8, 32(%rsp)
    movq    %rdx, 24(%rsp)
    leaq    24(%rsp), %rax
    movq    %rax, (%rsp)
    xorl    %eax, %eax
    testl    %ecx, %ecx
    je    LBB0_2
LBB0_1:                                 ## %.lr.ph
                                        ## =>This Inner Loop Header: Depth=1
    movq    (%rsp), %r8
    addq    $3, %r8
    andq    $-4, %r8
    leaq    4(%r8), %rdx
    movq    %rdx, (%rsp)
    addl    (%r8), %eax
    decl    %ecx
    jne    LBB0_1
LBB0_2:                                 ## %._crit_edge
    popq    %rdx
    retq


.subsections_via_symbols
========================

The stack walk is wrong (leaq, 4(%r8), %rdx).  It advances the pointer by 4
bytes each time - the sizeof(int).  On x86_64 the stack needs to be walked by
steps of 8 bytes.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20160506/9b664a3f/attachment.html>