gdb and strace show the buggy behavior on my machine.
Starting program: /cygdrive/e/verify/malloc/malltest.exe
Program received signal SIGSEGV, Segmentation fault. 0x61042e26 in strdup () from /usr/bin/cygwin1.dll (gdb) bt #0 0x61042e26 in strdup () from /usr/bin/cygwin1.dll #1 0x6104326b in mmap64 () from /usr/bin/cygwin1.dll #2 0x61043849 in mmap () from /usr/bin/cygwin1.dll #3 0x610401bc in mktime () from /usr/bin/cygwin1.dll #4 0x61040413 in mktime () from /usr/bin/cygwin1.dll #5 0x610413e6 in malloc () from /usr/bin/cygwin1.dll #6 0x004010e7 in main (argc=1, argv=0xa042630) at malltest.c:10
and
448 1192931 [main] malltest 1472 mmap64: 630000 = mmap() succeeded 249 1193180 [main] malltest 1472 mmap64: addr 0, len 1048576, prot 3, flags 22, fd -1, off 0 202 1193382 [main] malltest 1472 handle_exceptions: In cygwin_except_handler exc 0xC0000005 at 0x61042E26 sp 0x22FCB4 123 1193505 [main] malltest 1472 handle_exceptions: In cygwin_except_handler sig = 11 at 0x61042E26 118 1193623 [main] malltest 1472 handle_exceptions: In cygwin_except_handler calling 0x0 1193743 [main] malltest 1472 handle_exceptions: Exception: STATUS_ACCESS_VIOLATION 120 1193743 [main] malltest 1472 handle_exceptions: Exception: STATUS_ACCESS_VIOLATION
The wrapper from Bill Riemer's reply works, at least when I wrap my own malloc() calls.
More tips are still appreciated.
Best regards, Juergen
Ronald Landheer-Cieslak wrote:
Your code may have an unexpected side-effect: printf allocates memory as well. Try using this:
#include <stdlib.h>
int main(void) { void * x;
x = malloc(1000000);
while (x != NULL)
{
x = malloc(1000000);
if (x == NULL)
write(2, "malloc returned NULL\n", 21);
}
return(0);
}
I've tested it under gdb and with strace, both say "malloc returned NULL". OTOH, when simply run from the command-line, I do get a segmentation fault.
HTH
rlc
On Tue, Sep 02, 2003 at 03:35:04PM +0200, Juergen Bohn wrote:
Tested with cygwin1.dll 1.5.3-1 and 1.3.22-1 on Win2000-SP4, malloc() does not (always)
return NULL if there is no more memory available. Try, for example, simple loops like:
x = malloc(10000); for (i=0; x != NULL; i++) { x = malloc(10000); if (x == NULL) printf("x is NULL\n"); }
My application terminates with a segmentation violation, but all attempts to handle this by signal() or atexit() fail. Unfortunately, also sysconf() does not work to get the number of available pages (_SC_AVPHYS_PAGES, I get always the same but wrong value).
While testing, I detected that errno is set to 12 ("Not enough memory") after enough iterations through the for-loop above, while variable x still is not zero. But still my application crashes even when I break the loop at errno!=0.
Is there any secure way to find out, how much memory is available (or hope that the malloc() problems will be solved)?
Many thanks, Juergen
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