I'm using gettimeofday to get the most accurate time from the kernel
When I use calloc to create and initalize memory for the struct timeval *tv,
everything works fine:
struct timeval *tv;
tv = (struct timeval *)calloc(1, sizeof(struct timeval));
if (!tv) {
/* handle error... */
exit
}
gettimeofday(tv);
But, when I use malloc, gettimeofday segfaults, even though tv != NULL, and I
can set tv_sec and tv_usec manually without getting a segfault. Normally I'm
able to figure these kind of things out, but right now, I'm stuck. Especially
as it works if I use calloc and gettimeofday on a separate struct, or, if i
print the address of the malloc'ed timeval.
strace of program:
execve("./test_time", ["./test_time"], [/* 49 vars */]) = 0
brk(0) = 0x2330000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x7f42ca271000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x7f42ca26f000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or
directory)
open("tls/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
open("tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
open("x86_64/libc.s#include <stdio.h>
#include <stdlib.h>
/*
* struct timeval {
* time_t tv_sec;
* suseconds_t tv_usec;
* };
*/
void gettime_1(void)
{
struct timeval *tv;
tv = (struct timeval *)malloc(1*sizeof (struct timeval));
if (!tv) {
fprintf(stderr, "Could not allocate memory for timestruct\n");
return;
}
gettimeofday(tv);
printf("Time1: %lu, %lu\n", (long unsigned)tv->tv_sec, (long unsigned)tv-
>tv_usec);
}
void gettime_2(void)
{
struct timeval *tv;
tv = (struct timeval *)calloc(1,sizeof (struct timeval));
if (!tv) {
fprintf(stderr, "Could not allocate memory for timestruct\n");
return;
}
gettimeofday(tv);
printf("Time2: %lu, %lu\n", (long unsigned)tv->tv_sec, (long unsigned)tv-
>tv_usec);
}
int main (int argc, char *argv[])
{
gettime_1();
gettime_2();
return 0;
}
o.6", O_RDONLY) = -1 ENOENT (No such file or directory)
open("libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
open("/usr/lib32/tls/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat("/usr/lib32/tls/x86_64", 0x7fffd226fb20) = -1 ENOENT (No such file or
directory)
open("/usr/lib32/tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat("/usr/lib32/tls", 0x7fffd226fb20) = -1 ENOENT (No such file or
directory)
open("/usr/lib32/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat("/usr/lib32/x86_64", 0x7fffd226fb20) = -1 ENOENT (No such file or
directory)
open("/usr/lib32/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or
directory)
stat("/usr/lib32", {st_mode=S_IFDIR|0755, st_size=36864, ...}) = 0
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=115573, ...}) = 0
mmap(NULL, 115573, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f42ca252000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
directory)
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\345"..., 832) =
832
fstat(3, {st_mode=S_IFREG|0755, st_size=1502520, ...}) = 0
mmap(NULL, 3609304, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =
0x7f42c9ce2000
mprotect(0x7f42c9e4b000, 2093056, PROT_NONE) = 0
mmap(0x7f42ca04a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|
MAP_DENYWRITE, 3, 0x168000) = 0x7f42ca04a000
mmap(0x7f42ca04f000, 17112, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|
MAP_ANONYMOUS, -1, 0) = 0x7f42ca04f000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x7f42ca251000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x7f42ca250000
arch_prctl(ARCH_SET_FS, 0x7f42ca2506e0) = 0
mprotect(0x7f42ca04a000, 16384, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ) = 0
mprotect(0x7f42ca272000, 4096, PROT_READ) = 0
munmap(0x7f42ca252000, 115573) = 0
brk(0) = 0x2330000
brk(0x2351000) = 0x2351000
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++
Process 9387 detached
The program itself (note the usage of gettime_1 and gettime_2 (if I call
gettime_2 before gettime_1, it works, if I call gettime_1 first, it
segfaults).
#include <stdio.h>
#include <stdlib.h>
/*
* struct timeval {
* time_t tv_sec;
* suseconds_t tv_usec;
* };
*/
void gettime_1(void)
{
struct timeval *tv;
tv = (struct timeval *)malloc(1*sizeof (struct timeval));
if (!tv) {
fprintf(stderr, "Could not allocate memory for timestruct\n");
return;
}
gettimeofday(tv);
printf("Time1: %lu, %lu\n", (long unsigned)tv->tv_sec, (long unsigned)tv-
>tv_usec);
}
void gettime_2(void)
{
struct timeval *tv;
tv = (struct timeval *)calloc(1,sizeof (struct timeval));
if (!tv) {
fprintf(stderr, "Could not allocate memory for timestruct\n");
return;
}
gettimeofday(tv);
printf("Time2: %lu, %lu\n", (long unsigned)tv->tv_sec, (long unsigned)tv-
>tv_usec);
}
int main (int argc, char *argv[])
{
gettime_1();
gettime_2();
return 0;
}
Any help appreciated :-)
--
Henrik
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