Specify number size in gdb for print commands?

Question

To play around with various additions to registers that may be 8,4,2 or 1 bytes (rax, eax, ax, al) is there a way I can specify the number of bytes of the number I'm using? For example

# works for 4 bytes >>> p/x -1 $30 = 0xffffffff >>> p/x 1 $31 = 0x1 >>> p/d 0xffffffff $34 = -1 # can I get it to work for one byte, signed char? >>> p/d 0xff $35 = 255

kaylum · Accepted Answer · 2020-09-26 04:28:38Z

1

A simple way is to use casting to tell gdb the type of the value.

(gdb) p /d (char)0xff $2 = -1

answered Sep 26, 2020 at 4:28

kaylum

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2 Comments

samuelbrody1249 Over a year ago

thanks, could you please link to a part in the docs that explains that a bit if it's there? I tried help x and help p but wasn't finding too much of help.

kaylum Over a year ago

It's not really documented very explicitly as far as I know. The commands to examine data work on expressions. An expression is in the context of the language being debugged. In this case, the default type for C is int and casting is the way to change the type of any expression.

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