Re: [microblaze-uclinux] [patch] errno corruption

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Yashi,

Yasushi SHOJI wrote:

>>I expect it might be optimisation related - although I'm not sure why 
>>you and I would have different optimisation settings in the uClibc build...
> 
> ugaaaa, that's right. I have been using -Os instead of -O2!!!
> 
> -CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes -Wno-trigraphs -O2 \
> +CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes -Wno-trigraphs -Os \
> 
> sorry about that! I've totally forgot about it!

Heh happens all the time to me.  I've recently set up some structures 
here, where I maintain a pure CVS checkout (updated everynight with a 
cron job).  Then, I have various working distros to test etc.  Helps me 
keep track of what "everyone else" is seeing, vs whatever hacked local 
copy I'm using.

>>Anyway, the way forward:  I think we need to digest Dave's earlier email 
>>and do it properly - remove these assumptions that are causing the 
>>problem.  Basically that means rolling the syscall_return macro into the 
>>syscallN declarations, with inline assembly done properly.
> 
> 
> basically my second patch + macro move, right?
> 
> or do you want to implement in asm, so that we can optimise the way we
> want?

I think it should probably be done like in David's m68knommu example. 
Declare the variable __res, then inline asm to make the syscall, being 
explicit about the register allocations.  Here's a quick hack:

#define _syscall2(type, name, atype, a, btype, b)   \
  type name(atype a, btype b)                         \
     {                                                   \
       long __res;                                       \
       __asm__ __volatile__ ("addk  SYSCALL_ARG0, %2, r0  \n\t"     \
                             "addk  SYSCALL_ARG1, %3, r0  \n\t"     \
                             "bralid r17, 0x08            \n\t"	   \
                             "addik SYSCALL_NUM, r0, %1   \n\t"     \
                             "addk   %0, SYSCALL_RET, r0  \n\t"     \
                 :"=r" (__res)                          \
                 : "i" (__NR_##name),                    \
                   "r" ((long)a),                        \
                   "r" ((long)b)                         \
                 : "cc", "SYSCALL_RET", "SYSCALL_ARG0", "SYSCALL_ARG1", \
                         "SYSCALL_NUM");\
       if ((unsigned long)(__res) >= (unsigned long)(-125)) { \
         errno = -__res;                                 \
         __res = -1;                                     \
       }                                                 \
       return (type)__res;                               \
     }

Or something like it.  Note with this explicit approach we also get to 
use the delayslot on the bralid instruction, which is nice.  Also the 
syscall params should be mapped into exactly the same registers as for 
the function call that's making it, so it should produce some pretty 
streamlined assembly.

  > if you can tell me how you want, i can generate a patch. ;)

Great, well see if you can get my example above going, then map it into 
the syscall0 -> syscall5 macros

Thanks,

John

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