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

From: Michal Suchánek <[email-masked]>
Date: Thu, 29 Aug 2019 12:36:38 +0200

On Thu, 29 Aug 2019 12:23:42 +0200
Michal Suchanek <[email-masked]> wrote:

> 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
>  #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
>  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);
>  }

This will likely cause unreachable code on 32bit. Since there is need
for an ifdef and it cannot be inside condition the best is probably to
just split it to two separate conditions:

 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);
+#endif
 }