Question about gdb and memory addresses

Question

i am trying to use gdb to analyse a c program but i am a little confused. in the above picture you can see i am trying to analyse the stack . On the left we have memory addresses.Since i am using a 64 bit machine ,shouldn't ever memory address have 64 bits?but in the picture every memory location has 32 bits . Also the stack starts at 0x28fed0 and the second address is 0x28fee0 ,where are the address between these.I mean where is 0x28fed1? I studied architecture many years ago and i seem to be missing something basic. Can any one help me out?

thanks

Answer 1

The stack is not intrinsically 64-bit, it's just a memory area which can contains anything.

You specifically asked gdb to dump the memory in 32-bit quantities:

x/32xw

32 is the count (you can see that you've got 8 lines of 4 columns), x is output format (hexadecimal), and w is the item size ("word" - a 32-bit integer).

If you want to view memory as an array of 64-bit items, replace w by g ("giant word" or a 64-bit integer). To see individual bytes, use b.

As for addressing, each 32-bit item occupies four 8-bit bytes, so a row of four of them adds up to 4*4=16, or 0x10 bytes, that's why the next line starts at 0x28fee0. The byte at address 0x28fed1 is present inside the 32-bit word at 0x28fed0. Try dumping memory in different formats to get the feel for the data layout. Read up on little endian.