[Bug c++/45265] GCC has an intermittent bug when computing the address of function parameters

[rogerio at rilhas dot com]

------- Comment #22 from rogerio at rilhas dot com  2010-08-12 17:24 -------
(In reply to comment #21)
> Even without optimization (as the compilation script uses), the program
> crashes.

Right, that was the point of introducing the 1000-character buffer. With it it
crashes always.

>  To be concrete about what's going wrong based on what the assembly
> code actually looks like (GCC version Ubuntu 4.4.3-4ubuntu5):
> bug_example:
>     pushl    %ebp
>     movl    %esp, %ebp
>     subl    $1048, %esp         # space for buffer
>     movl    8(%ebp), %eax       # move string elsewhere
>     movl    %eax, -1020(%ebp)
>     movl    %gs:20, %eax        # stuff for stack checking
>     movl    %eax, -12(%ebp)
>     xorl    %eax, %eax
>     movb    $0, -1012(%ebp)
>     leal    12(%ebp), %eax      # address of i to stack
>     movl    %eax, 4(%esp)
>     leal    -1020(%ebp), %eax   # address of (copied) strp to stack
>     movl    %eax, (%esp)
>     call    bug_example_2
>     movl    -12(%ebp), %eax
>     xorl    %gs:20, %eax
>     je    .L6
>     call    __stack_chk_fail
> .L6:
>     leave
>     ret
>     .size    bug_example, .-bug_example
> You are assuming that in `bug_example' that the parameters passed to
> `bug_example_2' must be the addresses of those variables *as they were passed
> on the stack*.  This is certainly one way of implementing it, but it is not
> mandated by the standard (as comment #9 points out).

You are absolutelly right, I fully agree that a non-cdecl conformant GCC would
not need to pass parameters on the stack. It only has to pass parameters on the
stack (in a very well-defined way) if it claims to be cdecl-compliant. But even
with the cdecl specifier in the source the generated assembly code is wrong.
Hence a bug.

Hadn't you realized yet that that is my point from the start????


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45265