[fasmarm] rpi lower16 upper16

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shailesh

Joined: 13 Mar 2017
Posts: 2

shailesh 13 Mar 2017, 09:49

Hello,

does fasmarm have any support for extracting the upper16 and lower16 bits to write a macro to load a register with a 32 bit value directly?

Regards,
Shailesh

13 Mar 2017, 09:49

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19254
Location: In your JS exploiting you and your system

revolution 13 Mar 2017, 09:59

Assuming you are using 32-bit code then:

Code:

macro movlit reg,value {
  movw reg,(value) and 0xffff
  movt reg,(value) shr 16
}

movlit r0,0x12345678

13 Mar 2017, 09:59

shailesh

Joined: 13 Mar 2017
Posts: 2

shailesh 13 Mar 2017, 13:10

Thanks! Worked like a charm. The and and shr commands are, I am assuming, compiler specific. Can I find info about them in the fasm documentation? It wold be interesting to see what other commands I can use for implementing macros.

13 Mar 2017, 13:10

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 19254
Location: In your JS exploiting you and your system

revolution 13 Mar 2017, 13:38

fasmarm uses all the same operators as fasm. You'll need to check the fasm documentation for the basic assembler things and the specific fasmarm documentation for the ARM related stuff.

In essence you'll get:

and
or
xor
not
shl
shr
bsr
*
/
+
-
etc.

See the fasm manual for the precedence rules.

13 Mar 2017, 13:38

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