small example



I thought the above push rax should push qword rax (2 dwords) onto stack and that the printf would read these correctly, but it prints an incorrect result.

Can someone show me how to do this ?

Also, with 32-bit pe, how can I get value of rax into a memory location?

I've tried


and

but nothing seems to work

Many thanks

You can't use 64-bit code while running in 32-bit mode. The situation is even worse than when trying to use 16-bit code, which at least is accessible by NOT using use16 so fasm insert the appropriate override prefixes for the instructions.

So is use64 simply to revert to 64-bit after use32 in a 64-bit app?

Actually, use* are meant to be used when some portion of code will be run by the CPU in a mode other than the current one. For instance, if you were writing a DOS app and you switch to 32-bit protected mode, you'd need use32 for the code that will run after the mode switch, otherwise the processor won't interpret the instructions correctly because fasm (or any other assembler for that matter), assembled it assuming the CPU works in 16-bit mode all the time.

Using use32 in a 64-bit app would also be wrong, because again, if the CPU is running in 64-bit mode then instructions like "INC EAX" assembled in a use32 context will be interpreted by the CPU as a REX prefix, among many other problems caused by using incorrect instruction encodings for the mode the processor is running in.

Thanks for clearing that up for me loco.