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Message-ID: <ZYXDdlF1CFNpDdiV@LeoBras>
Date: Fri, 22 Dec 2023 14:12:22 -0300
From: Leonardo Bras <leobras@...hat.com>
To: Guo Ren <guoren@...nel.org>
Cc: Leonardo Bras <leobras@...hat.com>,
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 05:35:20PM +0800, Guo Ren wrote:
> 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>
Thanks!
Leo
>
> --
> Best Regards
> Guo Ren
>
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