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Message-ID: <CAJF2gTQNE7OQiAbkvVNzo9PCV=Xr8KQD0_=s-G56QMZJiZnjvA@mail.gmail.com>
Date: Fri, 22 Dec 2023 17:35:20 +0800
From: Guo Ren <guoren@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>, Eric Biederman <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>,
Conor Dooley <conor.dooley@...rochip.com>, Andy Chiu <andy.chiu@...ive.com>,
Greg Ungerer <gerg@...nel.org>, Vincent Chen <vincent.chen@...ive.com>,
Xiao Wang <xiao.w.wang@...el.com>, Charlie Jenkins <charlie@...osinc.com>,
Andrew Morton <akpm@...ux-foundation.org>, Alexandre Ghiti <alexghiti@...osinc.com>,
Kemeng Shi <shikemeng@...weicloud.com>, David Hildenbrand <david@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>, Qinglin Pan <panqinglin2020@...as.ac.cn>,
Greentime Hu <greentime.hu@...ive.com>, Björn Töpel <bjorn@...osinc.com>,
Clément Léger <cleger@...osinc.com>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [RFC PATCH 2/4] riscv: add compile-time test into is_compat_task()
On Fri, Dec 22, 2023 at 5:02 PM Leonardo Bras <leobras@...hat.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@...hat.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@...nel.org>
--
Best Regards
Guo Ren
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