>>> On 03.07.18 at 10:46, <david.lai...@aculab.com> wrote: > From: Jan Beulich >> Sent: 03 July 2018 09:36 > ... >> As said there, omitting suffixes from instructions in AT&T mode is bad >> practice when operand size cannot be determined by the assembler from >> register operands, and is likely going to be warned about by upstream >> gas in the future (mine does already). > ... >> - bt $9, EFLAGS(%rsp) /* interrupts off? */ >> + btl $9, EFLAGS(%rsp) /* interrupts off? */ > > Hmmm.... > Does the operand size make any difference at all for the bit instructions? > I'm pretty sure that the cpus (386 onwards) have always done aligned 32bit > transfers (the docs never actually said aligned). > I can't remember whether 64bit mode allows immediates above 31. > > So gas accepting 'btb $n,memory' is giving a false impression of > what actually happens.
BTB does not exist at all. BTW and (on 64-bit) BTQ do exist though, and they have behavior differing from BTL. The only AT&T syntax doc I have says that L is the default suffix to be used, but there are cases where this wasn't (and maybe still isn't) the case, so omitting a suffix when register operands aren't available to size instructions has always been a risky game. Jan
