Re: [RFC PATCH 2/4] riscv: add compile-time test into is_compat_task()

[Leonardo Bras <leobras@redhat.com>]

On Fri, Dec 22, 2023 at 05:35:20PM +0800, Guo Ren wrote:
> On Fri, Dec 22, 2023 at 5:02 PM Leonardo Bras <leobras@redhat.com> wrote:
> >
> > Currently several places will test for CONFIG_COMPAT before testing
> > is_compat_task(), probably in order to avoid a run-time test into the task
> > structure.
> >
> > Since is_compat_task() is an inlined function, it would be helpful to add a
> > compile-time test of CONFIG_COMPAT, making sure it always returns zero when
> > the option is not enabled during the kernel build.
> >
> > With this, the compiler is able to understand in build-time that
> > is_compat_task() will always return 0, and optimize-out some of the extra
> > code introduced by the option.
> >
> > This will also allow removing a lot #ifdefs that were introduced, and make
> > the code more clean.
> >
> > Signed-off-by: Leonardo Bras <leobras@redhat.com>
> > ---
> >  arch/riscv/include/asm/compat.h    | 3 +++
> >  arch/riscv/include/asm/elf.h       | 4 ----
> >  arch/riscv/include/asm/pgtable.h   | 6 ------
> >  arch/riscv/include/asm/processor.h | 4 ++--
> >  4 files changed, 5 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
> > index 2ac955b51148f..91517b51b8e27 100644
> > --- a/arch/riscv/include/asm/compat.h
> > +++ b/arch/riscv/include/asm/compat.h
> > @@ -14,6 +14,9 @@
> >
> >  static inline int is_compat_task(void)
> >  {
> > +       if (!IS_ENABLED(CONFIG_COMPAT))
> > +               return 0;
> > +
> >         return test_thread_flag(TIF_32BIT);
> >  }
> >
> > diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> > index 59a08367fddd7..2e88257cafaea 100644
> > --- a/arch/riscv/include/asm/elf.h
> > +++ b/arch/riscv/include/asm/elf.h
> > @@ -53,13 +53,9 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
> >  #define ELF_ET_DYN_BASE                ((DEFAULT_MAP_WINDOW / 3) * 2)
> >
> >  #ifdef CONFIG_64BIT
> > -#ifdef CONFIG_COMPAT
> >  #define STACK_RND_MASK         (is_compat_task() ? \
> >                                  0x7ff >> (PAGE_SHIFT - 12) : \
> >                                  0x3ffff >> (PAGE_SHIFT - 12))
> > -#else
> > -#define STACK_RND_MASK         (0x3ffff >> (PAGE_SHIFT - 12))
> > -#endif
> >  #endif
> >
> >  /*
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index 1d472b31e0cfe..ea5b269be223a 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -127,16 +127,10 @@
> >  #define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1))
> >  #define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
> >
> > -#ifdef CONFIG_COMPAT
> >  #define MMAP_VA_BITS_64 ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
> >  #define MMAP_MIN_VA_BITS_64 (VA_BITS_SV39)
> >  #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
> >  #define MMAP_MIN_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_MIN_VA_BITS_64)
> > -#else
> > -#define MMAP_VA_BITS ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
> > -#define MMAP_MIN_VA_BITS (VA_BITS_SV39)
> > -#endif /* CONFIG_COMPAT */
> > -
> >  #else
> >  #include <asm/pgtable-32.h>
> >  #endif /* CONFIG_64BIT */
> > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > index f19f861cda549..ed32e53e55999 100644
> > --- a/arch/riscv/include/asm/processor.h
> > +++ b/arch/riscv/include/asm/processor.h
> > @@ -22,7 +22,7 @@
> >  ({                                                             \
> >         unsigned long mmap_end;                                 \
> >         typeof(addr) _addr = (addr);                            \
> > -       if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> > +       if ((_addr) == 0 || is_compat_task())                   \
> >                 mmap_end = STACK_TOP_MAX;                       \
> >         else if ((_addr) >= VA_USER_SV57)                       \
> >                 mmap_end = STACK_TOP_MAX;                       \
> > @@ -39,7 +39,7 @@
> >         typeof(addr) _addr = (addr);                            \
> >         typeof(base) _base = (base);                            \
> >         unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base);   \
> > -       if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> > +       if ((_addr) == 0 || is_compat_task())                   \
> >                 mmap_base = (_base);                            \
> >         else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
> >                 mmap_base = VA_USER_SV57 - rnd_gap;             \
> > --
> > 2.43.0
> >
> Reviewed-by: Guo Ren <guoren@kernel.org>

Thanks!
Leo

> 
> -- 
> Best Regards
>  Guo Ren
>