CODEWITHSUNDEEP
assemblygdb
Koinos
Koinos

Reputation: 301

Size of a hex in GDB's x memory-dump command

I'm trying to try all the variants of the x command in assembly. I typed

(gdb) x /x $rsp
0x7fffffffdf90: 0x01

According to my book the x/x command select the first 8 bytes from rsp and write them as an hex. However, looking for the assembly documentation (gdb help) i have not found anywhere that the size of /x is explicitly 8 byte. So how do I know if it is really 8 bytes ?

Upvotes: 0

Views: 332

Answers (1)

Employed Russian
Employed Russian

Reputation: 213935

So how do I know if it is really 8 bytes ?

It's not. It's "whatever size you used last". Documentation.

For example:

(gdb) x/bx $rsp
0x7fffffffcbc8: 0x1c

Subsequent x/x commands will use size 1 (a single char):

(gdb) x/x $rsp
0x7fffffffcbc8: 0x1c

You can override the size explicitly:

(gdb) x/gx $rsp
0x7fffffffcbc8: 0x00007ffff7ddc61c

Subsequent x/x commands now default to size 8:

(gdb) x/x $rsp
0x7fffffffcbc8: 0x00007ffff7ddc61c

Upvotes: 2

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