Howdy,
I ran into a weird issue today while playing around with pmap. In an
effort to better understand the memory organization of a process, I
created a test program [1] to malloc() memory, and to print the address
where the memory is located. When I run my test program, I get the
following output:
$ ./foo &
Touching memory pages starting at address 209f8
[1] 5890
To see where memory (especially the heap) is located, I ran pmap against
the process:
$ pmap -x 5890
5890: ./foo
Address Kbytes RSS Anon Locked Mode Mapped File
00010000 8 8 - - r-x-- foo
00020000 8 8 8 - rwx-- foo
00022000 1032 1032 1032 - rwx-- [ heap ]
FF280000 864 808 - - r-x-- libc.so.1
FF368000 32 32 32 - rwx-- libc.so.1
FF370000 8 8 8 - rwx-- libc.so.1
FF380000 8 8 8 - rwx-- [ anon ]
FF398000 16 16 - - r-x-- libc_psr.so.1
FF3A0000 24 16 16 - rwx-- [ anon ]
FF3B0000 184 184 - - r-x-- ld.so.1
FF3EE000 8 8 8 - rwx-- ld.so.1
FF3F0000 8 8 8 - rwx-- ld.so.1
FFBFE000 8 8 8 - rw--- [ stack ]
-------- ------- ------- ------- -------
total Kb 2208 2144 1128 -
If the heap starts at address 22000, how can the chunk of memory I
allocated start at address 209f8?
Thanks for any insight,
- Ryan
[1]
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char**argv)
{
int i;
char *a = (char *) malloc(1024 *1024);
printf("Touching memory pages starting at address %0x\n",a);
for (i = 0; i < 1024 * 1024; i += 8192) {
a[i] = 23;
}
sleep(300);
}
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