severity 563882 important
retitle 563882 ia64: memchr overshots
thanks
On Tue, Jan 26, 2010 at 01:48:34PM -0600, Jonathan Nieder wrote:
> severity 563882 critical
Please explain. git is neither unrelated to glibc nor does this cause
serious data loss.
> That is, it maps the file into memory and looks for null bytes.
No, the kernel always maps complete pages, so this maps several null
bytes.
> Then this program would lie to you and say “M.out is binary”
The test program does not properly show what is going on.
The following program shows the cause:
| #include <sys/stat.h>
| #include <sys/mman.h>
| #include <fcntl.h>
|
| int main(int argc, const char * const argv[])
| {
| struct stat st;
| lstat(argv[1], &st);
|
| int fd = open(argv[1], O_RDONLY);
| void *data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
| void *t = memchr(data, 0, st.st_size);
| printf("ptr: %p, ret: %p, len: 0x%zx\n", data, t, st.st_size);
| return 0;
| }
Example output:
| % ./test /etc/passwd
| ptr: 0x2000000000050000, ret: 0x200000000005040e, len: 0x40e
The found location is already after the buffer. memchr is AFAIK expanded
by gcc.
Bastian
--
Where there's no emotion, there's no motive for violence.
-- Spock, "Dagger of the Mind", stardate 2715.1
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