[Syllable-kernel] Need help

[Kristian V. <kri...@xe...>]

I'm currently testing Glibc 2.3.3, and as part of that I am trying
to rebuild Gcc 3.3.4 against the new libs.  I've run into a problem
which is now beginning to look like a bug with Glibc 2.3.3, but I'm
totally stumped.

I've got it down to the following testcase:

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

FILE *y;

int main( int argc, char *argv[] )
{
  FILE *x;

  printf("x\n");
  x = fopen(argv[0],"r");
  fclose(x);
  printf("x closed\n");

  if( NULL == y )
  {
    printf("y is NULL\n");
    return EXIT_FAILURE;
  }
  printf("y\n");
  y = fopen(argv[0],"r");
  fclose(y);
  printf("y closed\n");

  return EXIT_SUCCESS;
}

Output is:

$ ./fopen
x
x closed
y
Segmentation fault (core dumped)
$ 

If you're paying attention, it actually crashes when it gets the the
if( NULL == y ) with a NULL pointer:

0:fopen::fopen : Invalid pagefault at 00000000 (NOTP:READ:USER)
0:fopen::fopen : EAX = 00000000 : EBX = 8000185c : ECX = 00000009 : EDX =
a00e4aa0
0:fopen::fopen : ESI = 00000001 : EDI = ffffbb2c : EBP = ffffbaac
0:fopen::fopen : SS::ESP = 0023::ffffba90
0:fopen::fopen : CS::EIP = 0013::800006b5
0:fopen::fopen : DS = 0023 : ES = 0023 : FS = 0023 : GS = 00d0
0:fopen::fopen : EFLAGS = 00213286 (PF SF IF RF ID )
0:fopen::fopen : CPU ID = 0 : kernel stack = 051c5014
0:fopen::fopen : 0 -> 800006b5
0:fopen::fopen :    fopen + 000006b5 -> __gmon_start__ + 800006b5
0:fopen::fopen : 1 -> a00143e1
0:fopen::fopen :    libc.so.2 + 000143e1 -> __libc_start_main + 000000a1
0:fopen::fopen : 2 -> 80000435
0:fopen::fopen :    fopen + 00000435 -> __gmon_start__ + 80000435
0:fopen::fopen : verify_area() got kernel address 00000000
0:fopen::fopen : 
0:fopen::fopen : Areas :
0:fopen::fopen : Area 0000 (10239) -> 80000000-80000fff 04ca7cd8 01 ro_fopen
0:fopen::fopen : Area 0001 (10240) -> 80001000-80001fff 04ca7cd8 01 rw_fopen
0:fopen::fopen : Area 0002 (10244) -> 88000000-88022fff 00000000 01 heap
0:fopen::fopen : Area 0003 (10241) -> a0000000-a00e3fff 04ca7ad8 01
ro_libc.so.2
0:fopen::fopen : Area 0004 (10242) -> a00e4000-a00eafff 04ca7ad8 01
rw_libc.so.2
0:fopen::fopen : Area 0005 (10243) -> ffc00000-ffffffff 00000000 01
main_stack
0:fopen::fopen : 0 -> 800006b5
0:fopen::fopen :    fopen + 000006b5 -> __gmon_start__ + 800006b5
0:fopen::fopen : 1 -> a00143e1
0:fopen::fopen :    libc.so.2 + 000143e1 -> __libc_start_main + 000000a1
0:fopen::fopen : 2 -> 80000435
0:fopen::fopen :    fopen + 00000435 -> __gmon_start__ + 80000435
0:fopen::fopen : verify_area() got kernel address 00000000
0:fopen::fopen : Killed by signal 11

Through experimentation I've found:

o If the declaration of y is moved inside main() it works.
o If y is declared as static FILE *y, it works.

This is what is causing me so much trouble; the scope of the variable is
relevent to the bug.  I could understand it if the crash was being caused
when fopen() tries to assign the value to y, but it crashes *whenever the
code goes anywhere near y*.  This, of course, is impossible.  At least, it
is highly improbable.

I need a linker/asm guru fast.  Can anyone explain why the scope of the
variable would have any relevence, and how it could cause this?

-- 
Vanders
http://www.syllable.org
http://www.liqwyd.com

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