Some small addition: On Thu, 28 Oct 2010 16:25:59 +0200, Thomas Schatzl <tom_at_w...@gmx.at> wrote: > Hi, > > On Thu, 28 Oct 2010 08:28:16 -0500, Andrew Brunner > <andrew.t.brun...@gmail.com> wrote: >> I tried to use the assembly code from the x64 unit on a i386 build of >> FPC but FPC throws error on compile. Why are the specific x64 >> instructions being blocked? The cpu running the code has the ability > > In general, the 32 and 64 bit instructions partially use the same opcode > for different actual instructions depending on the processor mode. The code > segment selector contains information about the type of instruction set > used. > It might be worth a try to hack a REX prefix in 32 bit assembly and see > what happens, but I'd assume that either you get an invalid opcode > exception or the prefix is just ignored.
Actually, the REX prefix uses the 32 bit inc/dec opcode space (0x40-0x4f) - so you *will* get an invalid opcode in the best case, and if you are lucky, some unwanted program behavior. Hth, Thomas _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
