Compile source code with GNU C Compiler (gcc)
gcc -o vars vars.cRun the executable file
./varsExamine the variables memory addresses and values stored in those addresses
gdb varsGNU gdb (Raspbian 8.2.1-2) 8.2.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from vars...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/pi/source/examine-variables/vars
points is 27 and is stored at 0xbefff4fc
year is 2020 and is stored at 0xbefff4f8
Program received signal SIGINT, Interrupt.
__GI_raise (sig=2) at ../sysdeps/unix/sysv/linux/raise.c:50
50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) x/3xw 0xbefff4f8
0xbefff4f8: 0x000007e4 0x0000001b 0x00000000
years = 0x000007e4 = 2020 (in decimal)
points = 0x0000001b = 27 (in decimal)
Same thing, this time printing the values in decimal format
(gdb) x/3dw 0xbefff4f8
0xbefff4f8: 2020 27 0
Same thing, this time in series of bytes (in little-endian data storage)
(gdb) x/12xb 0xbefff4f8
0xbefff4f8: 0xe4 0x07 0x00 0x00 0x1b 0x00 0x00 0x00
0xbefff500: 0x00 0x00 0x00 0x00
gdb vars
GNU gdb (Raspbian 8.2.1-2) 8.2.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from vars...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/pi/source/examine-variables/vars
points is 27 and is stored at 0xbefff4fc
year is 2020 and is stored at 0xbefff4f8
Program received signal SIGINT, Interrupt.
__GI_raise (sig=2) at ../sysdeps/unix/sysv/linux/raise.c:50
50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) i proc mapping
process 4698
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x10000 0x11000 0x1000 0x0 /home/pi/source/examine-variables/vars
0x20000 0x21000 0x1000 0x0 /home/pi/source/examine-variables/vars
0x21000 0x22000 0x1000 0x1000 /home/pi/source/examine-variables/vars
0x22000 0x43000 0x21000 0x0 [heap]
0xb6e57000 0xb6f8f000 0x138000 0x0 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6f8f000 0xb6f9f000 0x10000 0x138000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6f9f000 0xb6fa1000 0x2000 0x138000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6fa1000 0xb6fa2000 0x1000 0x13a000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6fa2000 0xb6fa5000 0x3000 0x0
0xb6fb9000 0xb6fbd000 0x4000 0x0 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fbd000 0xb6fcc000 0xf000 0x4000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fcc000 0xb6fcd000 0x1000 0x3000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fcd000 0xb6fce000 0x1000 0x4000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fce000 0xb6fee000 0x20000 0x0 /lib/arm-linux-gnueabihf/ld-2.28.so
0xb6ff9000 0xb6ffb000 0x2000 0x0
0xb6ffb000 0xb6ffc000 0x1000 0x0 [sigpage]
0xb6ffc000 0xb6ffd000 0x1000 0x0 [vvar]
0xb6ffd000 0xb6ffe000 0x1000 0x0 [vdso]
0xb6ffe000 0xb6fff000 0x1000 0x20000 /lib/arm-linux-gnueabihf/ld-2.28.so
0xb6fff000 0xb7000000 0x1000 0x21000 /lib/arm-linux-gnueabihf/ld-2.28.so
0xbefdf000 0xbf000000 0x21000 0x0 [stack]
points ... is stored at 0xbefff4fc
year ... is stored at 0xbefff4f8
the memory range 0xbefdf000 0xbf000000 (where our variables are stored) is allocated for the stack
gcc -o vars-heap vars-heap.cgdb vars-heap
GNU gdb (Raspbian 8.2.1-2) 8.2.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from vars-heap...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/pi/source/examine-variables/vars-heap
points is 27 and is stored at 0xbefff4ec
year is 2020 and is stored at 0xbefff4e8
data is 0x00022558 and is stored at 0xbefff4e4
Program received signal SIGINT, Interrupt.
__GI_raise (sig=2) at ../sysdeps/unix/sysv/linux/raise.c:50
50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) i p mapp
Ambiguous info command "p mapp": pretty-printer, probes, proc, program.
(gdb) i pro mapp
Ambiguous info command "pro mapp": probes, proc, program.
(gdb) i proc mapp
process 4811
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x10000 0x11000 0x1000 0x0 /home/pi/source/examine-variables/vars-heap
0x20000 0x21000 0x1000 0x0 /home/pi/source/examine-variables/vars-heap
0x21000 0x22000 0x1000 0x1000 /home/pi/source/examine-variables/vars-heap
0x22000 0x43000 0x21000 0x0 [heap]
0xb6e57000 0xb6f8f000 0x138000 0x0 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6f8f000 0xb6f9f000 0x10000 0x138000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6f9f000 0xb6fa1000 0x2000 0x138000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6fa1000 0xb6fa2000 0x1000 0x13a000 /lib/arm-linux-gnueabihf/libc-2.28.so
0xb6fa2000 0xb6fa5000 0x3000 0x0
0xb6fb9000 0xb6fbd000 0x4000 0x0 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fbd000 0xb6fcc000 0xf000 0x4000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fcc000 0xb6fcd000 0x1000 0x3000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fcd000 0xb6fce000 0x1000 0x4000 /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so
0xb6fce000 0xb6fee000 0x20000 0x0 /lib/arm-linux-gnueabihf/ld-2.28.so
0xb6ff9000 0xb6ffb000 0x2000 0x0
0xb6ffb000 0xb6ffc000 0x1000 0x0 [sigpage]
0xb6ffc000 0xb6ffd000 0x1000 0x0 [vvar]
0xb6ffd000 0xb6ffe000 0x1000 0x0 [vdso]
0xb6ffe000 0xb6fff000 0x1000 0x20000 /lib/arm-linux-gnueabihf/ld-2.28.so
0xb6fff000 0xb7000000 0x1000 0x21000 /lib/arm-linux-gnueabihf/ld-2.28.so
0xbefdf000 0xbf000000 0x21000 0x0 [stack]
data is 0x00022558 (HEAP) and is stored at 0xbefff4e4 (STACK)
the memory range 0x22000 0x43000 (where our pointer variable is stored) is allocated for the heap
0xbefff4e4 is stack address
0x00022558 is the value stored in this stack address that points to another address in the heap