Re: Bad xasm in __lwp_getprivate_fast

[Matt Thomas <matt%3am-software.com@localhost>]

On Oct 15, 2014, at 12:47 PM, Anders Magnusson <ragge%ludd.ltu.se@localhost> wrote:

> Matt Thomas skrev den 2014-10-15 17:42:
>> On Oct 15, 2014, at 3:06 AM, Anders Magnusson <ragge%ludd.ltu.se@localhost> wrote:
>> 
>>> While doing some testing I came across this not-so-correct extended assembler in mcontext.h:
>>> 
>>> static __inline void *
>>> __lwp_getprivate_fast(void)
>>> {
>>>        register void *tcb __asm("r0");
>>>        __asm("chmk %0" :: "i"(SYS__lwp_getprivate) : "r0");
>>>        return tcb;
>>> }
>>> 
>>> The result from chmk will be in r0.
>>> 
>>> The asm line says that r0 will be destroyed in the asm statement. In this particular case it will most likely work because gcc handles tcb as an uninitialized variable and it will get the r0 value anyway as long as the code is not reordered (which it may be). If tcb is assigned 0 before the asm statement it will fail.
>>> 
>>> Correct would be to write something like
>>> 
>>> __asm("chmk %0" : "=r"(tcb): "i"(SYS__lwp_getprivate));
>>> 
>>> which tells that the result will be in tcb (e.g. r0).
>>> 
>>> Comments?  Otherwise I will go ahead and fix this.
>> That won't do the right thing since that will emit chmk %r0.
> Yetch, of course not, it should be %1.  Thanks.

The problem is that %0 isn't referenced and it may not be r0.

Maybe combining the two?