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

[Nicholas Piggin <npiggin@gmail.com>]

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@suse.de>

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.

> 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?

Thanks,
Nick