Differences between current version and predecessor to the previous major change 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 8 | Last edited on Sunday, November 14, 2004 12:20:47 pm | by AristotlePagaltzis | Revert |
@@ -1,56 +1,73 @@
-The [Linux] VirtualMemory Map (as seen by a UserSpace program)
-
-| __Starts at__ | __Contains__
-| ffffffff |< End of the universe
-| ffffe000 |< vsyscall table (new in 2.5.x)
-| c0000000 |< Off limits, reserved for the kernel
-| bfffffff |< Process stack (grows down)
-| bffff000 |< Process heap (grows up)
-| 40000000 |< Libraries
-| zzzzzzzz |< Unused
-| yyyyyyyy |< __.bss__, uninitialised program data
-| xxxxxxxx |< __.data__ segment, initialised program data
-| 08048000 |< __.text__ segment, program code
-| 00000000 |< Unmapped to trap [NULL] pointers
-
+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>
+| bfffffff |< Process stack (grows down)<br>
+| bffff000 |< Process heap (grows up)<br>
+| 40000000 |< Libraries<br>
+| zzzzzzzz |< Unused<br>
+| 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))
+<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
+!Program code<br>
+<verbatim>
$ cat > x.c
+
#include <stdio.h>
int main(void) {printf("%p\n", main);return 0;}
$ gcc -o x x.c && ./x
0x8048344
$
+</verbatim>
(this is printing the address of the main function.)
!Process Heap
+<verbatim>
$ cat > x2.c
+
#include <stdio.h>
int main(void) {char c;printf("%p\n", &c); return 0;}
$ gcc -o x2 x2.c && ./x2
0xbffffab7
+</verbatim>
!Process Data and bss segment
+
+<verbatim>
$ perl -e 'my $var; print \$var . "\n"'
- SCALAR(0x814f38c)
+ SCALAR(0x814f38c)<br>
+</verbatim>
(note that this is the address in the [Perl] interpreter)
+<verbatim>
$ cat > x3.c
+
#include <stdio.h>
#include <stdlib.h>
int main(void) {char *p=!malloc(3);printf("%p\n", p); return 0;}
$ gcc -o x3 x3.c && ./x3
0x8049628
-
+</verbatim>
Also,
+<verbatim>
cat /proc/''pid''/maps
+</verbatim>
gives you the memory map for a program :)
