Created attachment 5726 [details]
sample code

Description of problem:
If error_one_per_line is set to a non-zero value, and error_at_line(3) is called consecutively with the same lineno, once with a NULL filename and the other non-NULL (in either order), the program SEGVs.  GDB shows the function uses strcmp(3) without checking for NULL inputs.


Version-Release number of selected component (if applicable):
Fedora 14: glibc-2.13-1.i686


How reproducible:
Always.


Steps to Reproduce:
1. gcc -Wall error-segv.c && ./a.out


Actual results:
./a.out: error_at_line with NULL filename: No such file or directory
Segmentation fault (core dumped)

Program received signal SIGSEGV, Segmentation fault.
__strcmp_ia32 () at ../sysdeps/i386/i686/strcmp.S:39
39	L(oop):	movb	(%ecx), %al
(gdb) bt
#0  __strcmp_ia32 () at ../sysdeps/i386/i686/strcmp.S:39
#1  0x0070eea6 in __error_at_line (status=0, errnum=2, 
    file_name=0x80485b9 "error-segv.c", line_number=10, message=0x8048594 "%s")
    at error.c:275
#2  0x080484bf in error_at_line () at /usr/include/bits/error.h:72
#3  main () at error-segv.c:10


Expected results:
Since NULL != __FILE__, the error_one_per_line clause should not be triggered, and output should be generated.


Additional info:
Neither http://www.gnu.org/s/libc/manual/html_node/Error-Messages.html nor http://www.kernel.org/doc/man-pages/online/pages/man3/error.3.html give any indication that filename cannot be NULL; my tests show that without setting error_one_per_line, or even set with two consecutive NULL filenames, it works fine.