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

["froydnj at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #21 from froydnj at gcc dot gnu dot org  2010-08-12 17:08 -------
Even without optimization (as the compilation script uses), the program
crashes.  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).


-- 


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