[RFC PATCH 07/13] um: nommu: configure fs register on host syscall invocation

[Hajime Tazaki]

On Fri, 25 Oct 2024 18:28:01 +0900,
Johannes Berg wrote:
> 
> On Thu, 2024-10-24 at 21:09 +0900, Hajime Tazaki wrote:
> > 
> > +static void sigill(int sig, siginfo_t *si, void *ctx_void)
> > +{
> > +	longjmp(jmpbuf, 1);
> > +}
> 
> Should this code use sigsetjmp/siglongjmp?

the code is referred from tools/testing/selftests/x86/fsgsbase.c and
the original code uses sigsetjmp/siglongjmp indeed.

I was struggling to pull the definition of sigsetjmp & co from host
headers as it conflicts with UML definitions of jmp_buf, etc.

Will look into detail again but would be nice if you have an
experience on this.

> > +int os_has_fsgsbase(void)
> > +{
> > +	return has_fsgsbase;
> > +}
> 
> Why should this be a function rather than just exposing the variable?

as it is referred in arch/x86/um code.

> > +++ b/arch/um/os-Linux/time.c
> > @@ -89,7 +89,8 @@ long long os_nsecs(void)
> >  {
> >  	struct timespec ts;
> >  
> > -	clock_gettime(CLOCK_MONOTONIC,&ts);
> > +	clock_gettime(CLOCK_MONOTONIC, &ts);
> > +
> >  	return timespec_to_ns(&ts);
> 
> unrelated changes

will revert it.

> >  #ifndef CONFIG_MMU
> >  
> > +static int os_x86_arch_prctl(int pid, int option, unsigned long *arg2)
> > +{
> > +	if (os_has_fsgsbase()) {
> > +		switch (option) {
> > +		case ARCH_SET_FS:
> > +			wrfsbase(*arg2);
> > +			break;
> > +		case ARCH_SET_GS:
> > +			wrgsbase(*arg2);
> > +			break;
> > +		case ARCH_GET_FS:
> > +			*arg2 = rdfsbase();
> > +			break;
> > +		case ARCH_GET_GS:
> > +			*arg2 = rdgsbase();
> > +			break;
> > +		}
> > +		return 0;
> > +	} else
> > +		return os_arch_prctl(pid, option, arg2);
> 
> please use (or don't) {} on all branches

thanks, will fix it.

> > @@ -39,4 +73,5 @@ __visible void do_syscall_64(struct pt_regs *regs)
> >  			current_thread_info()->aux_fp_regs);
> >  	}
> >  }
> > +
> >  #endif
> 
> unrelated

will revert it too.

-- Hajime