Differences between current version and revision by previous author of MemoryMap.
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| Newer page: | version 10 | Last edited on Tuesday, March 20, 2007 12:56:45 pm | by PerryLorier | |
| Older page: | version 9 | Last edited on Tuesday, March 20, 2007 3:42:10 am | by DeanDavis | Revert |
@@ -1,6 +1,7 @@
The [Linux] VirtualMemory Map (as seen by a UserSpace program)<br>
<code>
+<?plugin OldStyleTable
| __Starts at__| __Contains__<br>
| ffffffff |< End of the universe<br>
| ffffe000 |< vsyscall table (new in 2.5.x)<br>
| c0000000 |< Off limits, reserved for the kernel<br>
@@ -11,50 +12,62 @@
| yyyyyyyy |< __.bss__, uninitialised program data<br>
| xxxxxxxx |< __.data__ segment, initialised program data<br>
| 08048000 |< __.text__ segment, program code<br>
| 00000000 |< Unmapped to trap [NULL] pointers<br><br>
+?>
</code>
"BSS" means __b__lock __s__tarted by __s__ymbol and is a segment of uninitialised that is only stored in the BinaryExecutable image as a length and offset, since it would otherwise waste space. The "text" segment on the other hand contains ''initialized'' global variables and ''is'' stored in the BinaryExecutable.
!!Practical examples
!Library-mapped memory (using ldd(1))
-
$ ldd /bin/ls<br>
- librt.so.1 => /lib/librt.so.1 (0x40026000)<br>
- libc.so.6 => /lib/libc.so.6 (0x40038000)<br>
- libpthread.so.0 => /lib/libpthread.so.0 (0x4016a000)<br>
- /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)<br
>
+<verbatim>
+
$ ldd /bin/ls
+ librt.so.1 => /lib/librt.so.1 (0x40026000)
+ libc.so.6 => /lib/libc.so.6 (0x40038000)
+ libpthread.so.0 => /lib/libpthread.so.0 (0x4016a000)
+ /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
+
</verbatim
>
!Program code<br>
-
$ cat > x.c<br>
+<verbatim>
+
$ cat > x.c
- #include <stdio.h><br
>
- int main(void) {printf("%p\n", main);return ;}<br>
- $ gcc -o x x.c && ./x<br>
- 0x8048344<br>
- $<br
>
-(this is printing the address of the main function.)<br>
+ #include <stdio.h>
+ int main(void) {printf("%p\n", main);return ;}
+ $ gcc -o x x.c && ./x
+ 0x8048344
+ $
+
</verbatim
>
+(this is printing the address of the main function.)
!Process Heap
-
$ cat > x2.c<br>
-<code>
- #include <stdio.h><br
>
- int main(void) {char c;printf("%p\n", &c); return ;}<br></code>
- $ gcc -o x2 x2.c && ./x2<br>
- 0xbffffab7<br
>
+<verbatim>
+
$ cat > x2.c
+
+ #include <stdio.h>
+ int main(void) {char c;printf("%p\n", &c); return ;}
+ $ gcc -o x2 x2.c && ./x2
+ 0xbffffab7
+
</verbatim
>
!Process Data and bss segment
-
$ perl -e 'my $var; print \$var . "\n"'<br>
+<verbatim>
+
$ perl -e 'my $var; print \$var . "\n"'
SCALAR(0x814f38c)<br>
-(note that this is the address in the [Perl] interpreter)<br>
+</verbatim>
+
(note that this is the address in the [Perl] interpreter)
+<verbatim>
$ cat > x3.c
- #include <stdio.h><br
>
- #include <stdlib.h><br
>
- int main(void) {char *p=!malloc(3);printf("%p\n", p); return ;}<br>
- $ gcc -o x3 x3.c && ./x3<br>
- 0x8049628<br
>
-
+ #include <stdio.h>
+ #include <stdlib.h>
+ int main(void) {char *p=!malloc(3);printf("%p\n", p); return ;}
+ $ gcc -o x3 x3.c && ./x3
+ 0x8049628
+
</verbatim
>
Also,
+<verbatim>
cat /proc/''pid''/maps
+</verbatim>
gives you the memory map for a program :)
