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References: <20220721021127.1086628-1-yijun@loongson.cn> <CAAhV-H4YL-8tj+-329tWguwxrPaL7DpiTT2QkXBPh_feT7M5jA@mail.gmail.com>
 <dcfac9ad-d6e0-b157-4f11-cc2d3e2f1376@xen0n.name>
In-Reply-To: <dcfac9ad-d6e0-b157-4f11-cc2d3e2f1376@xen0n.name>
From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Thu, 21 Jul 2022 11:22:47 +0800
Message-ID: <CAAhV-H6RGZwKjV4Shm9fvH_XJ1+yqq9KpxkXNEWwOaPRmahSLQ@mail.gmail.com>
Subject: Re: [PATCH] LoongArch: Remove unused header compiler.h
To:     WANG Xuerui <kernel@xen0n.name>
Cc:     Jun Yi <yijun@loongson.cn>, loongarch@lists.linux.dev,
        LKML <linux-kernel@vger.kernel.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
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Hi, Xuerui,

On Thu, Jul 21, 2022 at 11:17 AM WANG Xuerui <kernel@xen0n.name> wrote:
>
> Hi YI Jun and Huacai,
>
> On 2022/7/21 10:52, Huacai Chen wrote:
> > Hi, Jun,
> >
> > On Thu, Jul 21, 2022 at 10:11 AM Jun Yi <yijun@loongson.cn> wrote:
> >> Loongarch not used arch-specific compiler.h
> > I'm not sure whether compiler.h will be used in future. If it will be
> > used, I want to keep it as is. Xuerui, what do you think about it?
>
> I surveyed all the existing arch compiler.h in the tree:
>
> $ find ./arch -name compiler.h
> ./arch/alpha/include/asm/compiler.h
> ./arch/alpha/include/uapi/asm/compiler.h
> ./arch/arm/include/asm/compiler.h
> ./arch/arm64/include/asm/compiler.h
> ./arch/mips/include/asm/compiler.h
> ./arch/loongarch/include/asm/compiler.h
>
> Of all these occurrences:
>
> - alpha needs to ensure a certain insn is being emitted from time to
> time, with plain C constructs (or built-ins) on compiler versions with
> said support, falling back to inline asm otherwise;
> - arm and arm64 both need some inline assembly help (of different sort),
> with arm64 stuffing some pointer authentication helpers into this file too;
> - mips, which is obviously what the loongarch version is based on, needs
> (1) a kludge for older compilers to fix delay slot filling around
> __builtin_unreachable, (2) definitions for explicit arch level
> selection. There is also the historical GCC_OFF_SMALL_ASM() constraint
> definition that was rendered redundant by commit 4abaacc704729 ("MIPS:
> remove GCC < 4.9 support").
>
> For loongarch, the "ZC" constraint (I don't think it was a coincidence
> BTW) should be usable for all present and future hardware, so I do think
> the GCC_OFF_SMALL_ASM() here is redundant. We may want to remove the
> mips one too. And the arch level thing is not currently needed either,
> future revisions to the LoongArch ISA should be largely backwards
> compatible, so it could be a long time before such explicit selection of
> arch level is necessary, for exact control over emitted insn.
>
> So overall, I'm in favor of removing this header for now.
Have you considered the new relocation types will be added in the near
future? I think we need compiler.h at that time.

Huacai
>
> > Huacai
> >> Signed-off-by: Jun Yi <yijun@loongson.cn>
> >> ---
> >>   arch/loongarch/Kconfig                |  1 -
> >>   arch/loongarch/include/asm/atomic.h   |  9 ++++-----
> >>   arch/loongarch/include/asm/compiler.h | 15 ---------------
> >>   arch/loongarch/include/asm/futex.h    |  5 ++---
> >>   arch/loongarch/include/asm/irqflags.h |  1 -
> >>   arch/loongarch/include/asm/local.h    |  1 -
> >>   arch/loongarch/kernel/reset.c         |  1 -
> >>   arch/loongarch/lib/delay.c            |  1 -
> >>   8 files changed, 6 insertions(+), 28 deletions(-)
> >>   delete mode 100644 arch/loongarch/include/asm/compiler.h
> >>
> >> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> >> index 53a912befb62..89da3e09084e 100644
> >> --- a/arch/loongarch/Kconfig
> >> +++ b/arch/loongarch/Kconfig
> >> @@ -69,7 +69,6 @@ config LOONGARCH
> >>          select GENERIC_TIME_VSYSCALL
> >>          select GPIOLIB
> >>          select HAVE_ARCH_AUDITSYSCALL
> >> -       select HAVE_ARCH_COMPILER_H
> >>          select HAVE_ARCH_MMAP_RND_BITS if MMU
> >>          select HAVE_ARCH_SECCOMP_FILTER
> >>          select HAVE_ARCH_TRACEHOOK
> >> diff --git a/arch/loongarch/include/asm/atomic.h b/arch/loongarch/include/asm/atomic.h
> >> index 979367ad4e2c..b5e2e3201af1 100644
> >> --- a/arch/loongarch/include/asm/atomic.h
> >> +++ b/arch/loongarch/include/asm/atomic.h
> >> @@ -10,7 +10,6 @@
> >>   #include <linux/types.h>
> >>   #include <asm/barrier.h>
> >>   #include <asm/cmpxchg.h>
> >> -#include <asm/compiler.h>
> >>
> >>   #if __SIZEOF_LONG__ == 4
> >>   #define __LL           "ll.w   "
> >> @@ -164,7 +163,7 @@ static inline int arch_atomic_sub_if_positive(int i, atomic_t *v)
> >>                  "2:                                                     \n"
> >>                  __WEAK_LLSC_MB
> >>                  : "=&r" (result), "=&r" (temp),
> >> -                 "+" GCC_OFF_SMALL_ASM() (v->counter)
> >> +                 "+ZC" (v->counter)
> >>                  : "I" (-i));
> >>          } else {
> >>                  __asm__ __volatile__(
> >> @@ -177,7 +176,7 @@ static inline int arch_atomic_sub_if_positive(int i, atomic_t *v)
> >>                  "2:                                                     \n"
> >>                  __WEAK_LLSC_MB
> >>                  : "=&r" (result), "=&r" (temp),
> >> -                 "+" GCC_OFF_SMALL_ASM() (v->counter)
> >> +                 "+ZC" (v->counter)
> >>                  : "r" (i));
> >>          }
> >>
> >> @@ -327,7 +326,7 @@ static inline long arch_atomic64_sub_if_positive(long i, atomic64_t *v)
> >>                  "2:                                                     \n"
> >>                  __WEAK_LLSC_MB
> >>                  : "=&r" (result), "=&r" (temp),
> >> -                 "+" GCC_OFF_SMALL_ASM() (v->counter)
> >> +                 "+ZC" (v->counter)
> >>                  : "I" (-i));
> >>          } else {
> >>                  __asm__ __volatile__(
> >> @@ -340,7 +339,7 @@ static inline long arch_atomic64_sub_if_positive(long i, atomic64_t *v)
> >>                  "2:                                                     \n"
> >>                  __WEAK_LLSC_MB
> >>                  : "=&r" (result), "=&r" (temp),
> >> -                 "+" GCC_OFF_SMALL_ASM() (v->counter)
> >> +                 "+ZC" (v->counter)
> >>                  : "r" (i));
> >>          }
> >>
> >> diff --git a/arch/loongarch/include/asm/compiler.h b/arch/loongarch/include/asm/compiler.h
> >> deleted file mode 100644
> >> index 657cebe70ace..000000000000
> >> --- a/arch/loongarch/include/asm/compiler.h
> >> +++ /dev/null
> >> @@ -1,15 +0,0 @@
> >> -/* SPDX-License-Identifier: GPL-2.0 */
> >> -/*
> >> - * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> >> - */
> >> -#ifndef _ASM_COMPILER_H
> >> -#define _ASM_COMPILER_H
> >> -
> >> -#define GCC_OFF_SMALL_ASM() "ZC"
> >> -
> >> -#define LOONGARCH_ISA_LEVEL "loongarch"
> >> -#define LOONGARCH_ISA_ARCH_LEVEL "arch=loongarch"
> >> -#define LOONGARCH_ISA_LEVEL_RAW loongarch
> >> -#define LOONGARCH_ISA_ARCH_LEVEL_RAW LOONGARCH_ISA_LEVEL_RAW
> >> -
> >> -#endif /* _ASM_COMPILER_H */
> >> diff --git a/arch/loongarch/include/asm/futex.h b/arch/loongarch/include/asm/futex.h
> >> index 9de8231694ec..e28b65d9c67a 100644
> >> --- a/arch/loongarch/include/asm/futex.h
> >> +++ b/arch/loongarch/include/asm/futex.h
> >> @@ -8,7 +8,6 @@
> >>   #include <linux/futex.h>
> >>   #include <linux/uaccess.h>
> >>   #include <asm/barrier.h>
> >> -#include <asm/compiler.h>
> >>   #include <asm/errno.h>
> >>
> >>   #define __futex_atomic_op(insn, ret, oldval, uaddr, oparg)             \
> >> @@ -95,8 +94,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 oldval, u32 newv
> >>          "       "__UA_ADDR "\t1b, 4b                            \n"
> >>          "       "__UA_ADDR "\t2b, 4b                            \n"
> >>          "       .previous                                       \n"
> >> -       : "+r" (ret), "=&r" (val), "=" GCC_OFF_SMALL_ASM() (*uaddr)
> >> -       : GCC_OFF_SMALL_ASM() (*uaddr), "Jr" (oldval), "Jr" (newval),
> >> +       : "+r" (ret), "=&r" (val), "=ZC" (*uaddr)
> >> +       : "ZC" (*uaddr), "Jr" (oldval), "Jr" (newval),
> >>            "i" (-EFAULT)
> >>          : "memory", "t0");
> >>
> >> diff --git a/arch/loongarch/include/asm/irqflags.h b/arch/loongarch/include/asm/irqflags.h
> >> index 52121cd791fe..319a8c616f1f 100644
> >> --- a/arch/loongarch/include/asm/irqflags.h
> >> +++ b/arch/loongarch/include/asm/irqflags.h
> >> @@ -9,7 +9,6 @@
> >>
> >>   #include <linux/compiler.h>
> >>   #include <linux/stringify.h>
> >> -#include <asm/compiler.h>
> >>   #include <asm/loongarch.h>
> >>
> >>   static inline void arch_local_irq_enable(void)
> >> diff --git a/arch/loongarch/include/asm/local.h b/arch/loongarch/include/asm/local.h
> >> index 2052a2267337..65fbbae9fc4d 100644
> >> --- a/arch/loongarch/include/asm/local.h
> >> +++ b/arch/loongarch/include/asm/local.h
> >> @@ -9,7 +9,6 @@
> >>   #include <linux/bitops.h>
> >>   #include <linux/atomic.h>
> >>   #include <asm/cmpxchg.h>
> >> -#include <asm/compiler.h>
> >>
> >>   typedef struct {
> >>          atomic_long_t a;
> >> diff --git a/arch/loongarch/kernel/reset.c b/arch/loongarch/kernel/reset.c
> >> index 2b86469e4718..800c965a17ea 100644
> >> --- a/arch/loongarch/kernel/reset.c
> >> +++ b/arch/loongarch/kernel/reset.c
> >> @@ -13,7 +13,6 @@
> >>   #include <linux/console.h>
> >>
> >>   #include <acpi/reboot.h>
> >> -#include <asm/compiler.h>
> >>   #include <asm/idle.h>
> >>   #include <asm/loongarch.h>
> >>   #include <asm/reboot.h>
> >> diff --git a/arch/loongarch/lib/delay.c b/arch/loongarch/lib/delay.c
> >> index 5d856694fcfe..831d4761f385 100644
> >> --- a/arch/loongarch/lib/delay.c
> >> +++ b/arch/loongarch/lib/delay.c
> >> @@ -7,7 +7,6 @@
> >>   #include <linux/smp.h>
> >>   #include <linux/timex.h>
> >>
> >> -#include <asm/compiler.h>
> >>   #include <asm/processor.h>
> >>
> >>   void __delay(unsigned long cycles)
> >> --
> >> 2.31.1
> >>
> >>