Re: [PATCH 31/33] powerpc/64: make buildable without CONFIG_COMPAT

[Michal Suchánek]

On Wed, Nov 13, 2019 at 01:02:34PM +1000, Nicholas Piggin wrote:
> Michal Suchanek's on November 13, 2019 2:52 am:
> > There are numerous references to 32bit functions in generic and 64bit
> > code so ifdef them out.
> > 
> > Signed-off-by: Michal Suchanek <msuchanek@xxxxxxx>
> 
> For the most part these seem okay to me.
> 
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index 45f1d5e54671..35874119b398 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -44,16 +44,16 @@ CFLAGS_btext.o += -DDISABLE_BRANCH_PROFILING
> >  endif
> >  
> >  obj-y				:= cputable.o ptrace.o syscalls.o \
> > -				   irq.o align.o signal_32.o pmc.o vdso.o \
> > +				   irq.o align.o signal_$(BITS).o pmc.o vdso.o \
> >  				   process.o systbl.o idle.o \
> >  				   signal.o sysfs.o cacheinfo.o time.o \
> >  				   prom.o traps.o setup-common.o \
> >  				   udbg.o misc.o io.o misc_$(BITS).o \
> >  				   of_platform.o prom_parse.o
> > -obj-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
> > -				   signal_64.o ptrace32.o \
> > +obj-$(CONFIG_PPC64)		+= setup_64.o \
> >  				   paca.o nvram_64.o firmware.o note.o \
> >  				   syscall_64.o
> > +obj-$(CONFIG_COMPAT)		+= sys_ppc32.o ptrace32.o signal_32.o
> >  obj-$(CONFIG_VDSO32)		+= vdso32/
> >  obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o
> >  obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> > index 00173cc904ef..c339a984958f 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -52,8 +52,10 @@
> >  SYS_CALL_TABLE:
> >  	.tc sys_call_table[TC],sys_call_table
> >  
> > +#ifdef CONFIG_COMPAT
> >  COMPAT_SYS_CALL_TABLE:
> >  	.tc compat_sys_call_table[TC],compat_sys_call_table
> > +#endif
> >  
> >  /* This value is used to mark exception frames on the stack. */
> >  exception_marker:
> > diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> > index 60436432399f..61678cb0e6a1 100644
> > --- a/arch/powerpc/kernel/signal.c
> > +++ b/arch/powerpc/kernel/signal.c
> > @@ -247,7 +247,6 @@ static void do_signal(struct task_struct *tsk)
> >  	sigset_t *oldset = sigmask_to_save();
> >  	struct ksignal ksig = { .sig = 0 };
> >  	int ret;
> > -	int is32 = is_32bit_task();
> >  
> >  	BUG_ON(tsk != current);
> >  
> > @@ -277,7 +276,7 @@ static void do_signal(struct task_struct *tsk)
> >  
> >  	rseq_signal_deliver(&ksig, tsk->thread.regs);
> >  
> > -	if (is32) {
> > +	if (is_32bit_task()) {
> >          	if (ksig.ka.sa.sa_flags & SA_SIGINFO)
> >  			ret = handle_rt_signal32(&ksig, oldset, tsk);
> >  		else
> 
> This is just a clean up I guess.

It also expands directly to if(0) or if(1) for the !COMPAT cases. I am
not sure how it would work with the intermediate variable.

There was more complex change initially but after some additional
cleanups removing the variable is the only part left.

> 
> > diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
> > index d00cfc4a39a9..319ebd4f494d 100644
> > --- a/arch/powerpc/kernel/syscall_64.c
> > +++ b/arch/powerpc/kernel/syscall_64.c
> > @@ -17,7 +17,6 @@ typedef long (*syscall_fn)(long, long, long, long, long, long);
> >  
> >  long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8, unsigned long r0, struct pt_regs *regs)
> >  {
> > -	unsigned long ti_flags;
> >  	syscall_fn f;
> >  
> >  	if (IS_ENABLED(CONFIG_PPC_BOOK3S))
> > @@ -64,8 +63,7 @@ long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8,
> >  
> >  	__hard_irq_enable();
> >  
> > -	ti_flags = current_thread_info()->flags;
> > -	if (unlikely(ti_flags & _TIF_SYSCALL_DOTRACE)) {
> > +	if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
> >  		/*
> >  		 * We use the return value of do_syscall_trace_enter() as the
> >  		 * syscall number. If the syscall was rejected for any reason
> > @@ -81,7 +79,7 @@ long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8,
> >  	/* May be faster to do array_index_nospec? */
> >  	barrier_nospec();
> >  
> > -	if (unlikely(ti_flags & _TIF_32BIT)) {
> > +	if (unlikely(is_32bit_task())) {
> >  		f = (void *)compat_sys_call_table[r0];
> >  
> >  		r3 &= 0x00000000ffffffffULL;
> 
> I guess this is okay, I did want to be careful about where ti_flags
> was loaded exactly, but I think DOTRACE and 32BIT are not volatile.
> Is it possible to define _TIF_32BIT to zero for 64-bit !compat case
> and have the original branch eliminated, or does that cause other
> problems?

is_32bit_task() expands to 0 or 1 constant unless CONFIG_COMPAT is set.
That's why the test needs replacing here.

Unsetting _TIF_32BIT might also be feasible but it is not necessary.

Thanks

Michal