Subject: Re: [PATCH v4 3/4] powerpc/64: make buildable without CONFIG_COMPAT

From: Michal Suchánek <[email-masked]>
Date: Thu, 29 Aug 2019 20:56:05 +0200

On Thu, 29 Aug 2019 19:40:55 +0200
Christophe Leroy <[email-masked]> wrote:

> Le 29/08/2019 à 12:23, Michal Suchanek a écrit :
> > There are numerous references to 32bit functions in generic and 64bit
> > code so ifdef them out.
> > 
> > Signed-off-by: Michal Suchanek <[email-masked]>
> > ---
> > v2:
> > - fix 32bit ifdef condition in signal.c
> > - simplify the compat ifdef condition in vdso.c - 64bit is redundant
> > - simplify the compat ifdef condition in callchain.c - 64bit is redundant
> > v3:
> > - use IS_ENABLED and maybe_unused where possible
> > - do not ifdef declarations
> > - clean up Makefile
> > v4:
> > - further makefile cleanup
> > - simplify is_32bit_task conditions
> > - avoid ifdef in condition by using return
> > ---
> >   arch/powerpc/include/asm/thread_info.h |  4 ++--
> >   arch/powerpc/kernel/Makefile           |  7 +++----
> >   arch/powerpc/kernel/entry_64.S         |  2 ++
> >   arch/powerpc/kernel/signal.c           |  3 +--
> >   arch/powerpc/kernel/syscall_64.c       |  6 ++----
> >   arch/powerpc/kernel/vdso.c             |  5 ++---
> >   arch/powerpc/perf/callchain.c          | 14 ++++++++++----
> >   7 files changed, 22 insertions(+), 19 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> > index 8e1d0195ac36..c128d8a48ea3 100644
> > --- a/arch/powerpc/include/asm/thread_info.h
> > +++ b/arch/powerpc/include/asm/thread_info.h
> > @@ -144,10 +144,10 @@ static inline bool test_thread_local_flags(unsigned int flags)
> >   	return (ti->local_flags & flags) != 0;
> >   }
> >   
> > -#ifdef CONFIG_PPC64
> > +#ifdef CONFIG_COMPAT
> >   #define is_32bit_task()	(test_thread_flag(TIF_32BIT))
> >   #else
> > -#define is_32bit_task()	(1)
> > +#define is_32bit_task()	(IS_ENABLED(CONFIG_PPC32))
> >   #endif
> >   
> >   #if defined(CONFIG_PPC64)
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index 1d646a94d96c..9d8772e863b9 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -44,16 +44,15 @@ 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-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
> > -				   signal_64.o ptrace32.o \
> > -				   paca.o nvram_64.o firmware.o \
> > +obj-$(CONFIG_PPC64)		+= setup_64.o paca.o nvram_64.o firmware.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 2ec825a85f5b..a2dbf216f607 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -51,8 +51,10 @@
> >   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
> > diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
> > index 98ed970796d5..0d5cbbe54cf1 100644
> > --- a/arch/powerpc/kernel/syscall_64.c
> > +++ b/arch/powerpc/kernel/syscall_64.c
> > @@ -38,7 +38,6 @@ 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;
> >   
> >   	BUG_ON(!(regs->msr & MSR_PR));
> > @@ -83,8 +82,7 @@ long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8,
> >   	 */
> >   	regs->softe = IRQS_ENABLED;
> >   
> > -	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
> > @@ -100,7 +98,7 @@ 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;
> > diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
> > index d60598113a9f..6d4a077f74d6 100644
> > --- a/arch/powerpc/kernel/vdso.c
> > +++ b/arch/powerpc/kernel/vdso.c
> > @@ -667,9 +667,7 @@ static void __init vdso_setup_syscall_map(void)
> >   {
> >   	unsigned int i;
> >   	extern unsigned long *sys_call_table;
> > -#ifdef CONFIG_PPC64
> >   	extern unsigned long *compat_sys_call_table;
> > -#endif
> >   	extern unsigned long sys_ni_syscall;
> >   
> >   
> > @@ -678,7 +676,8 @@ static void __init vdso_setup_syscall_map(void)
> >   		if (sys_call_table[i] != sys_ni_syscall)
> >   			vdso_data->syscall_map_64[i >> 5] |=
> >   				0x80000000UL >> (i & 0x1f);
> > -		if (compat_sys_call_table[i] != sys_ni_syscall)
> > +		if (IS_ENABLED(CONFIG_COMPAT) &&
> > +		    compat_sys_call_table[i] != sys_ni_syscall)
> >   			vdso_data->syscall_map_32[i >> 5] |=
> >   				0x80000000UL >> (i & 0x1f);
> >   #else /* CONFIG_PPC64 */
> > diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> > index c84bbd4298a0..aef8c750d242 100644
> > --- a/arch/powerpc/perf/callchain.c
> > +++ b/arch/powerpc/perf/callchain.c
> > @@ -15,7 +15,7 @@
> >   #include <asm/sigcontext.h>
> >   #include <asm/ucontext.h>
> >   #include <asm/vdso.h>
> > -#ifdef CONFIG_PPC64
> > +#ifdef CONFIG_COMPAT  
> 
> Is this ifdef needed at all ? Is it a problem to include it all the time ?

Yes, it is a problem. Some 32bit structures are not defined giving an
error.

> 
> >   #include "../kernel/ppc32.h"
> >   #endif
> >   #include <asm/pte-walk.h>
> > @@ -165,6 +165,7 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
> >   	return read_user_stack_slow(ptr, ret, 8);
> >   }
> >   
> > +__maybe_unused  
> 
> I don't like that too much. I see this function is almost identical 
> between PPC64 and PPC32. It should be possible to have only one, using 
> IS_ENABLED(CONFIG_PPC64) inside it to call read_user_stack_slow().
> An define a dummy read_user_stack_slow() for PPC32 as already done for 
> perf_callchain_user_64().

We need to #ifdef the block below anyway because it needs 32bit
structures defined which aren't. So can add usage there.

> 
> >   static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> >   {
> >   	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> > @@ -341,6 +342,7 @@ static inline int valid_user_sp(unsigned long sp, int is_64)
> >   
> >   #endif /* CONFIG_PPC64 */
> >   
> > +#if defined(CONFIG_PPC32) || defined(CONFIG_COMPAT)
> >   /*
> >    * Layout for non-RT signal frames
> >    */
> > @@ -482,12 +484,16 @@ static void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
> >   		sp = next_sp;
> >   	}
> >   }
> > +#endif /* 32bit */
> >   
> >   void
> >   perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
> >   {
> > -	if (current_is_64bit())
> > -		perf_callchain_user_64(entry, regs);
> > -	else
> > +#if defined(CONFIG_PPC32) || defined(CONFIG_COMPAT)
> > +	if (!current_is_64bit()) {
> >   		perf_callchain_user_32(entry, regs);
> > +		return;
> > +	}
> > +#endif
> > +	perf_callchain_user_64(entry, regs);
> >   }
> >   
> 
> Instead of that it could just be:
> 
> 	if (current_is_64bit())
> 		perf_callchain_user_64(entry, regs);
> 	else
> 		perf_callchain_user_32(entry, regs);
> 
> 
> By adding a dummy perf_callchain_user_32() when needed as already done 
> for perf_callchain_user_64()

and it can do a dummy use of the function above as well.

> And by making sure current_is_64bit() returns IS_ENABLED(CONFIG_PPC64) 
> when CONFIG_COMPAT is not set, on the same principle as you did for 
> is_32bit_task()
Yes, that would make it constant for the !COMPAT cases.
> 
> And maybe you could think about spliting callchain.c out in a 
> callchain_32.c and a callchain_64.c that gets selected by the Makefiles 
> based on the same principle as you did for ptrace_32.c etc...

I actually did not split those. Can look how splitting is done there
and if it can be applied to the callchain situation.

Thanks

Michal