Subject: Re: [PATCH v5 3/5] powerpc/64: make buildable without CONFIG_COMPAT

From: Michal Suchánek <[email-masked]>
Date: Fri, 30 Aug 2019 09:54:51 +0200

On Fri, 30 Aug 2019 06:35:13 +0000 (UTC)
Christophe Leroy <[email-masked]> wrote:

> On 08/29/2019 10:28 PM, Michal Suchanek 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
> > v5:
> > - avoid unreachable code on 32bit
> > - make is_current_64bit constant on !COMPAT
> > - add stub perf_callchain_user_32 to avoid some ifdefs
> > ---
> >   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          | 13 +++++++++++--
> >   7 files changed, 23 insertions(+), 17 deletions(-)
> >   
> [...]
> 
> > diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> > index c84bbd4298a0..881be5c4e9bb 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>
> > @@ -291,7 +291,8 @@ static inline int current_is_64bit(void)
> >   	 * interrupt stack, and the thread flags don't get copied over
> >   	 * from the thread_info on the main stack to the interrupt stack.
> >   	 */
> > -	return !test_ti_thread_flag(task_thread_info(current), TIF_32BIT);
> > +	return !IS_ENABLED(CONFIG_COMPAT) ||
> > +		!test_ti_thread_flag(task_thread_info(current), TIF_32BIT);
> >   }
> >   
> >   #else  /* CONFIG_PPC64 */
> > @@ -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
> >    */
> > @@ -482,6 +484,13 @@ static void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
> >   		sp = next_sp;
> >   	}
> >   }
> > +#else /* 32bit */
> > +static void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
> > +				   struct pt_regs *regs)
> > +{
> > +	(void)&read_user_stack_32; /* unused if !COMPAT */  
> 
> That looks pretty much like a hack.
> 
> See possible alternative below.
> 
> > +}
> > +#endif /* 32bit */
> >   
> >   void
> >   perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
> >   
> 
> ---
>  arch/powerpc/perf/callchain.c | 62 +++++++++++++++++++------------------------
>  1 file changed, 27 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> index 881be5c4e9bb..1b169b32776a 100644
> --- a/arch/powerpc/perf/callchain.c
> +++ b/arch/powerpc/perf/callchain.c
> @@ -165,22 +165,6 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
>  	return read_user_stack_slow(ptr, ret, 8);
>  }
>  
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> -{
> -	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> -	    ((unsigned long)ptr & 3))
> -		return -EFAULT;
> -
> -	pagefault_disable();
> -	if (!__get_user_inatomic(*ret, ptr)) {
> -		pagefault_enable();
> -		return 0;
> -	}
> -	pagefault_enable();
> -
> -	return read_user_stack_slow(ptr, ret, 4);
> -}
> -
>  static inline int valid_user_sp(unsigned long sp, int is_64)
>  {
>  	if (!sp || (sp & 7) || sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
> @@ -296,25 +280,10 @@ static inline int current_is_64bit(void)
>  }
>  
>  #else  /* CONFIG_PPC64 */
> -/*
> - * On 32-bit we just access the address and let hash_page create a
> - * HPTE if necessary, so there is no need to fall back to reading
> - * the page tables.  Since this is called at interrupt level,
> - * do_page_fault() won't treat a DSI as a page fault.
> - */
> -static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> -{
> -	int rc;
> -
> -	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> -	    ((unsigned long)ptr & 3))
> -		return -EFAULT;
>  
> -	pagefault_disable();
> -	rc = __get_user_inatomic(*ret, ptr);
> -	pagefault_enable();
> -
> -	return rc;
> +static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
> +{
> +	return 0;
>  }
>  
>  static inline void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
> @@ -344,6 +313,30 @@ static inline int valid_user_sp(unsigned long sp, int is_64)
>  
>  #if defined(CONFIG_PPC32) || defined(CONFIG_COMPAT)
>  /*
> + * On 32-bit we just access the address and let hash_page create a
> + * HPTE if necessary, so there is no need to fall back to reading
> + * the page tables.  Since this is called at interrupt level,
> + * do_page_fault() won't treat a DSI as a page fault.
> + */
> +static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
> +{
> +	int rc;
> +
> +	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
> +	    ((unsigned long)ptr & 3))
> +		return -EFAULT;
> +
> +	pagefault_disable();
> +	rc = __get_user_inatomic(*ret, ptr);
> +	pagefault_enable();
> +
> +	if (IS_ENABLED(CONFIG_PPC32) || !rc)
> +		return rc;
> +
> +	return read_user_stack_slow(ptr, ret, 4);
Which is not declared here. This is not intended to be the final state,
anyway.

Thanks

Michal
> +}
> +
> +/*
>   * Layout for non-RT signal frames
>   */
>  struct signal_frame_32 {
> @@ -488,7 +481,6 @@ static void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
>  static void perf_callchain_user_32(struct perf_callchain_entry_ctx *entry,
>  				   struct pt_regs *regs)
>  {
> -	(void)&read_user_stack_32; /* unused if !COMPAT */
>  }
>  #endif /* 32bit */
>