Ubuntu
gdb package

malloc scribbles on the stack of newly-compiled programs

Bug #176038 reported by eggshaped on 2007-12-13

Affects		Status	Importance	Assigned to	Milestone
	gcc	Invalid	Undecided	Unassigned
	gdb (Ubuntu)	Invalid	Undecided	Unassigned

Bug Description

Binary package hint: gcc

After a fresh install of gutsy desktop, I found that programs compiled on it (which would work fine when compiled and run other machines, such as my Intel OS X laptop) would crash with a corrupt stack almost immediately after they began running. (The programs in question were wxWidgets applications, one of my own and one sample "Hello, World!" app for testing.)

The actual stack-scribbling begins the first time the program hits malloc+83 (mov $0x1, %ecx) in libc, but since it only happens to programs I've compiled myself, I'm flagging this as a compiler bug. Note that it happens in both gcc and g++.

Here's the minimal test case:

// Compiled with just "gcc -g -o test test.c"
// gcc (GCC) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
// libc 2.6.1-1ubuntu10
// Linux 2.6.22-14-generic #1 SMP Sun Oct 14 23:05:12 GMT 2007 i686 GNU/Linux

#include <stdio.h>
#include <stdlib.h>

void wtf(int argc, char** argv) {
  // main()'s stack frame gets hosed as soon as the next line executes.
  char** myargv = (char**) malloc(sizeof(char*) * argc);
  int myargc = argc;
}

int main(int argc, char** argv) {
wtf(argc, argv);
return 0;
}

Debugger output:

(gdb) b wtf
Breakpoint 1 at 0x804837a: file test2.c, line 6.
(gdb) run
Starting program: /home/foo/test2

Breakpoint 1, wtf (argc=1, argv=0xbfdc2f24) at test2.c:6
6 char** myargv = (char**) malloc(sizeof(char*) * argc);
(gdb) bt
#0 wtf (argc=1, argv=0xbfdc2f24) at test2.c:6
#1 0x080483b5 in main (argc=1, argv=0xbfdc2f24) at test2.c:11 [looks OK...]
(gdb) n
7 int myargc = argc;
(gdb) bt
#0 wtf (argc=1, argv=0xbfdc2f24) at test2.c:7
#1 0x080483b5 in main (argc=0, argv=0x20ff1) at test2.c:11 [say what?]