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References: <20220514080402.2650181-1-chenhuacai@loongson.cn>
 <20220514080402.2650181-20-chenhuacai@loongson.cn> <5b14144a-9725-41db-7179-c059c41814cf@xen0n.name>
In-Reply-To: <5b14144a-9725-41db-7179-c059c41814cf@xen0n.name>
From:   Huacai Chen <chenhuacai@gmail.com>
Date:   Sun, 15 May 2022 22:52:02 +0800
Message-ID: <CAAhV-H7wV7tVBDSnVB9iLZpLhfx8mNgyKXy8wRZ+fKdUED2Xzw@mail.gmail.com>
Subject: Re: [PATCH V10 19/22] LoongArch: Add VDSO and VSYSCALL support
To:     WANG Xuerui <kernel@xen0n.name>
Cc:     Huacai Chen <chenhuacai@loongson.cn>,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Airlie <airlied@linux.ie>,
        Jonathan Corbet <corbet@lwn.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Yanteng Si <siyanteng@loongson.cn>,
        Guo Ren <guoren@kernel.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi, Xuerui,

On Sun, May 15, 2022 at 10:47 PM WANG Xuerui <kernel@xen0n.name> wrote:
>
> Hi,
>
> On 5/14/22 16:03, Huacai Chen wrote:
> > Add VDSO and VSYSCALL support (sigreturn, gettimeofday and its friends)
> > for LoongArch.
> >
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> > ---
> >   arch/loongarch/include/asm/vdso.h             |  38 +++++
> >   arch/loongarch/include/asm/vdso/clocksource.h |   8 +
> >   .../loongarch/include/asm/vdso/gettimeofday.h |  99 +++++++++++++
> >   arch/loongarch/include/asm/vdso/processor.h   |  14 ++
> >   arch/loongarch/include/asm/vdso/vdso.h        |  30 ++++
> >   arch/loongarch/include/asm/vdso/vsyscall.h    |  27 ++++
> >   arch/loongarch/kernel/vdso.c                  | 138 ++++++++++++++++++
> >   arch/loongarch/vdso/Makefile                  |  96 ++++++++++++
> >   arch/loongarch/vdso/elf.S                     |  15 ++
> >   arch/loongarch/vdso/gen_vdso_offsets.sh       |  13 ++
> >   arch/loongarch/vdso/sigreturn.S               |  24 +++
> >   arch/loongarch/vdso/vdso.S                    |  22 +++
> >   arch/loongarch/vdso/vdso.lds.S                |  72 +++++++++
> >   arch/loongarch/vdso/vgettimeofday.c           |  25 ++++
> >   14 files changed, 621 insertions(+)
> >   create mode 100644 arch/loongarch/include/asm/vdso.h
> >   create mode 100644 arch/loongarch/include/asm/vdso/clocksource.h
> >   create mode 100644 arch/loongarch/include/asm/vdso/gettimeofday.h
> >   create mode 100644 arch/loongarch/include/asm/vdso/processor.h
> >   create mode 100644 arch/loongarch/include/asm/vdso/vdso.h
> >   create mode 100644 arch/loongarch/include/asm/vdso/vsyscall.h
> >   create mode 100644 arch/loongarch/kernel/vdso.c
> >   create mode 100644 arch/loongarch/vdso/Makefile
> >   create mode 100644 arch/loongarch/vdso/elf.S
> >   create mode 100755 arch/loongarch/vdso/gen_vdso_offsets.sh
> >   create mode 100644 arch/loongarch/vdso/sigreturn.S
> >   create mode 100644 arch/loongarch/vdso/vdso.S
> >   create mode 100644 arch/loongarch/vdso/vdso.lds.S
> >   create mode 100644 arch/loongarch/vdso/vgettimeofday.c
> >
> > diff --git a/arch/loongarch/include/asm/vdso.h b/arch/loongarch/include/asm/vdso.h
> > new file mode 100644
> > index 000000000000..996bddae12dc
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso.h
> > @@ -0,0 +1,38 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#ifndef __ASM_VDSO_H
> > +#define __ASM_VDSO_H
> > +
> > +#include <linux/mm_types.h>
> > +#include <vdso/datapage.h>
> > +
> > +#include <asm/barrier.h>
> > +
> > +/**
> > + * struct loongarch_vdso_info - Details of a VDSO image.
> > + * @vdso: Pointer to VDSO image (page-aligned).
> > + * @size: Size of the VDSO image (page-aligned).
> > + * @off_rt_sigreturn: Offset of the rt_sigreturn() trampoline.
> > + * @code_mapping: Special mapping structure for vdso code.
> > + * @code_mapping: Special mapping structure for vdso data.
> > + *
> > + * This structure contains details of a VDSO image, including the image data
> > + * and offsets of certain symbols required by the kernel. It is generated as
> > + * part of the VDSO build process, aside from the mapping page array, which is
> > + * populated at runtime.
> > + */
> > +struct loongarch_vdso_info {
> > +     void *vdso;
> > +     unsigned long size;
> > +     unsigned long offset_sigreturn;
> > +     struct vm_special_mapping code_mapping;
> > +     struct vm_special_mapping data_mapping;
> > +};
> > +
> > +extern struct loongarch_vdso_info vdso_info;
> > +
> > +#endif /* __ASM_VDSO_H */
> > diff --git a/arch/loongarch/include/asm/vdso/clocksource.h b/arch/loongarch/include/asm/vdso/clocksource.h
> > new file mode 100644
> > index 000000000000..13cd580d406d
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso/clocksource.h
> > @@ -0,0 +1,8 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +#ifndef __ASM_VDSOCLOCKSOURCE_H
> > +#define __ASM_VDSOCLOCKSOURCE_H
> > +
> > +#define VDSO_ARCH_CLOCKMODES \
> > +     VDSO_CLOCKMODE_CPU
> > +
> > +#endif /* __ASM_VDSOCLOCKSOURCE_H */
> > diff --git a/arch/loongarch/include/asm/vdso/gettimeofday.h b/arch/loongarch/include/asm/vdso/gettimeofday.h
> > new file mode 100644
> > index 000000000000..5fc5a746b1c4
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso/gettimeofday.h
> > @@ -0,0 +1,99 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +#ifndef __ASM_VDSO_GETTIMEOFDAY_H
> > +#define __ASM_VDSO_GETTIMEOFDAY_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <asm/unistd.h>
> > +#include <asm/vdso/vdso.h>
> > +
> > +#define VDSO_HAS_CLOCK_GETRES                1
> > +
> > +static __always_inline long gettimeofday_fallback(
> > +                             struct __kernel_old_timeval *_tv,
> > +                             struct timezone *_tz)
> > +{
> > +     register struct __kernel_old_timeval *tv asm("a0") = _tv;
> > +     register struct timezone *tz asm("a1") = _tz;
> > +     register long nr asm("a7") = __NR_gettimeofday;
> > +     register long ret asm("v0");
> > +
> > +     asm volatile(
> > +     "       syscall 0\n"
> > +     : "=r" (ret)
> > +     : "r" (nr), "r" (tv), "r" (tz)
> > +     : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7",
> > +       "$t8", "memory");
> Here ret is being hinted to register $v0, which is in fact the same
> register as $a0; so I'm afraid the "=r" constraint wouldn't prevent the
> $a0 from being clobbered before the syscall insn? Changing "v0" to "a0",
> then "=r" to "+r", could do it, although I cannot build-test it (due to
> the boot protocol being incompatible with existing shipped systems).
> Please check this for me...
Thanks, all v0 will be replaced.

Huacai
> > +
> > +     return ret;
> > +}
> > +
> > +static __always_inline long clock_gettime_fallback(
> > +                                     clockid_t _clkid,
> > +                                     struct __kernel_timespec *_ts)
> > +{
> > +     register clockid_t clkid asm("a0") = _clkid;
> > +     register struct __kernel_timespec *ts asm("a1") = _ts;
> > +     register long nr asm("a7") = __NR_clock_gettime;
> > +     register long ret asm("v0");
> > +
> > +     asm volatile(
> > +     "       syscall 0\n"
> > +     : "=r" (ret)
> > +     : "r" (nr), "r" (clkid), "r" (ts)
> > +     : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7",
> > +       "$t8", "memory");
> > +
> > +     return ret;
> > +}
> > +
> > +static __always_inline int clock_getres_fallback(
> > +                                     clockid_t _clkid,
> > +                                     struct __kernel_timespec *_ts)
> > +{
> > +     register clockid_t clkid asm("a0") = _clkid;
> > +     register struct __kernel_timespec *ts asm("a1") = _ts;
> > +     register long nr asm("a7") = __NR_clock_getres;
> > +     register long ret asm("v0");
> > +
> > +     asm volatile(
> > +     "       syscall 0\n"
> > +     : "=r" (ret)
> > +     : "r" (nr), "r" (clkid), "r" (ts)
> > +     : "$t0", "$t1", "$t2", "$t3", "$t4", "$t5", "$t6", "$t7",
> > +       "$t8", "memory");
> > +
> > +     return ret;
> > +}
> > +
> > +static __always_inline u64 __arch_get_hw_counter(s32 clock_mode,
> > +                                              const struct vdso_data *vd)
> > +{
> > +     unsigned int count;
> > +
> > +     __asm__ __volatile__(
> > +     "       rdtime.d %0, $zero\n"
> > +     : "=r" (count));
> > +
> > +     return count;
> > +}
> > +
> > +static inline bool loongarch_vdso_hres_capable(void)
> > +{
> > +     return true;
> > +}
> > +#define __arch_vdso_hres_capable loongarch_vdso_hres_capable
> > +
> > +static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
> > +{
> > +     return get_vdso_data();
> > +}
> > +
> > +#endif /* !__ASSEMBLY__ */
> > +
> > +#endif /* __ASM_VDSO_GETTIMEOFDAY_H */
> > diff --git a/arch/loongarch/include/asm/vdso/processor.h b/arch/loongarch/include/asm/vdso/processor.h
> > new file mode 100644
> > index 000000000000..ef5770b343a0
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso/processor.h
> > @@ -0,0 +1,14 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +#ifndef __ASM_VDSO_PROCESSOR_H
> > +#define __ASM_VDSO_PROCESSOR_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#define cpu_relax()  barrier()
> > +
> > +#endif /* __ASSEMBLY__ */
> > +
> > +#endif /* __ASM_VDSO_PROCESSOR_H */
> > diff --git a/arch/loongarch/include/asm/vdso/vdso.h b/arch/loongarch/include/asm/vdso/vdso.h
> > new file mode 100644
> > index 000000000000..5a01643a65b3
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso/vdso.h
> > @@ -0,0 +1,30 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <asm/asm.h>
> > +#include <asm/page.h>
> > +
> > +static inline unsigned long get_vdso_base(void)
> > +{
> > +     unsigned long addr;
> > +
> > +     __asm__(
> > +     " la.pcrel %0, _start\n"
> > +     : "=r" (addr)
> > +     :
> > +     :);
> > +
> > +     return addr;
> > +}
> > +
> > +static inline const struct vdso_data *get_vdso_data(void)
> > +{
> > +     return (const struct vdso_data *)(get_vdso_base() - PAGE_SIZE);
> > +}
> > +
> > +#endif /* __ASSEMBLY__ */
> > diff --git a/arch/loongarch/include/asm/vdso/vsyscall.h b/arch/loongarch/include/asm/vdso/vsyscall.h
> > new file mode 100644
> > index 000000000000..5de615383a22
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/vdso/vsyscall.h
> > @@ -0,0 +1,27 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __ASM_VDSO_VSYSCALL_H
> > +#define __ASM_VDSO_VSYSCALL_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/timekeeper_internal.h>
> > +#include <vdso/datapage.h>
> > +
> > +extern struct vdso_data *vdso_data;
> > +
> > +/*
> > + * Update the vDSO data page to keep in sync with kernel timekeeping.
> > + */
> > +static __always_inline
> > +struct vdso_data *__loongarch_get_k_vdso_data(void)
> > +{
> > +     return vdso_data;
> > +}
> > +#define __arch_get_k_vdso_data __loongarch_get_k_vdso_data
> > +
> > +/* The asm-generic header needs to be included after the definitions above */
> > +#include <asm-generic/vdso/vsyscall.h>
> > +
> > +#endif /* !__ASSEMBLY__ */
> > +
> > +#endif /* __ASM_VDSO_VSYSCALL_H */
> > diff --git a/arch/loongarch/kernel/vdso.c b/arch/loongarch/kernel/vdso.c
> > new file mode 100644
> > index 000000000000..e20c8ca87473
> > --- /dev/null
> > +++ b/arch/loongarch/kernel/vdso.c
> > @@ -0,0 +1,138 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#include <linux/binfmts.h>
> > +#include <linux/elf.h>
> > +#include <linux/err.h>
> > +#include <linux/init.h>
> > +#include <linux/ioport.h>
> > +#include <linux/kernel.h>
> > +#include <linux/mm.h>
> > +#include <linux/random.h>
> > +#include <linux/sched.h>
> > +#include <linux/slab.h>
> > +#include <linux/timekeeper_internal.h>
> > +
> > +#include <asm/page.h>
> > +#include <asm/vdso.h>
> > +#include <vdso/helpers.h>
> > +#include <vdso/vsyscall.h>
> > +#include <generated/vdso-offsets.h>
> > +
> > +extern char vdso_start[], vdso_end[];
> > +
> > +/* Kernel-provided data used by the VDSO. */
> > +static union loongarch_vdso_data {
> > +     u8 page[PAGE_SIZE];
> > +     struct vdso_data data[CS_BASES];
> > +} loongarch_vdso_data __page_aligned_data;
> > +struct vdso_data *vdso_data = loongarch_vdso_data.data;
> > +static struct page *vdso_pages[] = { NULL };
> > +
> > +static int vdso_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
> > +{
> > +     current->mm->context.vdso = (void *)(new_vma->vm_start);
> > +
> > +     return 0;
> > +}
> > +
> > +struct loongarch_vdso_info vdso_info = {
> > +     .vdso = vdso_start,
> > +     .size = PAGE_SIZE,
> > +     .code_mapping = {
> > +             .name = "[vdso]",
> > +             .pages = vdso_pages,
> > +             .mremap = vdso_mremap,
> > +     },
> > +     .data_mapping = {
> > +             .name = "[vvar]",
> > +     },
> > +     .offset_sigreturn = vdso_offset_sigreturn,
> > +};
> > +
> > +static int __init init_vdso(void)
> > +{
> > +     unsigned long i, pfn;
> > +
> > +     BUG_ON(!PAGE_ALIGNED(vdso_info.vdso));
> > +     BUG_ON(!PAGE_ALIGNED(vdso_info.size));
> > +
> > +     pfn = __phys_to_pfn(__pa_symbol(vdso_info.vdso));
> > +     for (i = 0; i < vdso_info.size / PAGE_SIZE; i++)
> > +             vdso_info.code_mapping.pages[i] = pfn_to_page(pfn + i);
> > +
> > +     return 0;
> > +}
> > +subsys_initcall(init_vdso);
> > +
> > +static unsigned long vdso_base(void)
> > +{
> > +     unsigned long base = STACK_TOP;
> > +
> > +     if (current->flags & PF_RANDOMIZE) {
> > +             base += get_random_int() & (VDSO_RANDOMIZE_SIZE - 1);
> > +             base = PAGE_ALIGN(base);
> > +     }
> > +
> > +     return base;
> > +}
> > +
> > +int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> > +{
> > +     int ret;
> > +     unsigned long vvar_size, size, data_addr, vdso_addr;
> > +     struct mm_struct *mm = current->mm;
> > +     struct vm_area_struct *vma;
> > +     struct loongarch_vdso_info *info = current->thread.vdso;
> > +
> > +     if (mmap_write_lock_killable(mm))
> > +             return -EINTR;
> > +
> > +     /*
> > +      * Determine total area size. This includes the VDSO data itself
> > +      * and the data page.
> > +      */
> > +     vvar_size = PAGE_SIZE;
> > +     size = vvar_size + info->size;
> > +
> > +     data_addr = get_unmapped_area(NULL, vdso_base(), size, 0, 0);
> > +     if (IS_ERR_VALUE(data_addr)) {
> > +             ret = data_addr;
> > +             goto out;
> > +     }
> > +     vdso_addr = data_addr + PAGE_SIZE;
> > +
> > +     vma = _install_special_mapping(mm, data_addr, vvar_size,
> > +                                    VM_READ | VM_MAYREAD,
> > +                                    &info->data_mapping);
> > +     if (IS_ERR(vma)) {
> > +             ret = PTR_ERR(vma);
> > +             goto out;
> > +     }
> > +
> > +     /* Map VDSO data page. */
> > +     ret = remap_pfn_range(vma, data_addr,
> > +                           virt_to_phys(vdso_data) >> PAGE_SHIFT,
> > +                           PAGE_SIZE, PAGE_READONLY);
> > +     if (ret)
> > +             goto out;
> > +
> > +     /* Map VDSO code page. */
> > +     vma = _install_special_mapping(mm, vdso_addr, info->size,
> > +                                    VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
> > +                                    &info->code_mapping);
> > +     if (IS_ERR(vma)) {
> > +             ret = PTR_ERR(vma);
> > +             goto out;
> > +     }
> > +
> > +     mm->context.vdso = (void *)vdso_addr;
> > +     ret = 0;
> > +
> > +out:
> > +     mmap_write_unlock(mm);
> > +     return ret;
> > +}
> > diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile
> > new file mode 100644
> > index 000000000000..6b6e16732c60
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/Makefile
> > @@ -0,0 +1,96 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Objects to go into the VDSO.
> > +
> > +# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> > +# the inclusion of generic Makefile.
> > +ARCH_REL_TYPE_ABS := R_LARCH_32|R_LARCH_64|R_LARCH_MARK_LA|R_LARCH_JUMP_SLOT
> > +include $(srctree)/lib/vdso/Makefile
> > +
> > +obj-vdso-y := elf.o vgettimeofday.o sigreturn.o
> > +
> > +# Common compiler flags between ABIs.
> > +ccflags-vdso := \
> > +     $(filter -I%,$(KBUILD_CFLAGS)) \
> > +     $(filter -E%,$(KBUILD_CFLAGS)) \
> > +     $(filter -march=%,$(KBUILD_CFLAGS)) \
> > +     $(filter -m%-float,$(KBUILD_CFLAGS)) \
> > +     -D__VDSO__
> > +
> > +ifeq ($(cc-name),clang)
> > +ccflags-vdso += $(filter --target=%,$(KBUILD_CFLAGS))
> > +endif
> > +
> > +cflags-vdso := $(ccflags-vdso) \
> > +     $(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
> > +     -O2 -g -fno-strict-aliasing -fno-common -fno-builtin -G0 \
> > +     -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> > +     $(call cc-option, -fno-asynchronous-unwind-tables) \
> > +     $(call cc-option, -fno-stack-protector)
> > +aflags-vdso := $(ccflags-vdso) \
> > +     -D__ASSEMBLY__ -Wa,-gdwarf-2
> > +
> > +ifneq ($(c-gettimeofday-y),)
> > +  CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> > +endif
> > +
> > +# VDSO linker flags.
> > +ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
> > +     $(filter -E%,$(KBUILD_CFLAGS)) -nostdlib -shared \
> > +     --hash-style=sysv --build-id -T
> > +
> > +GCOV_PROFILE := n
> > +
> > +#
> > +# Shared build commands.
> > +#
> > +
> > +quiet_cmd_vdsold_and_vdso_check = LD      $@
> > +      cmd_vdsold_and_vdso_check = $(cmd_ld); $(cmd_vdso_check)
> > +
> > +quiet_cmd_vdsoas_o_S = AS       $@
> > +      cmd_vdsoas_o_S = $(CC) $(a_flags) -c -o $@ $<
> > +
> > +# Generate VDSO offsets using helper script
> > +gen-vdsosym := $(srctree)/$(src)/gen_vdso_offsets.sh
> > +quiet_cmd_vdsosym = VDSOSYM $@
> > +      cmd_vdsosym = $(NM) $< | $(gen-vdsosym) | LC_ALL=C sort > $@
> > +
> > +include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
> > +     $(call if_changed,vdsosym)
> > +
> > +#
> > +# Build native VDSO.
> > +#
> > +
> > +native-abi := $(filter -mabi=%,$(KBUILD_CFLAGS))
> > +
> > +targets += $(obj-vdso-y)
> > +targets += vdso.lds vdso.so.dbg vdso.so
> > +
> > +obj-vdso := $(obj-vdso-y:%.o=$(obj)/%.o)
> > +
> > +$(obj-vdso): KBUILD_CFLAGS := $(cflags-vdso) $(native-abi)
> > +$(obj-vdso): KBUILD_AFLAGS := $(aflags-vdso) $(native-abi)
> > +
> > +$(obj)/vdso.lds: KBUILD_CPPFLAGS := $(ccflags-vdso) $(native-abi)
> > +
> > +$(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE
> > +     $(call if_changed,vdsold_and_vdso_check)
> > +
> > +$(obj)/vdso.so: OBJCOPYFLAGS := -S
> > +$(obj)/vdso.so: $(obj)/vdso.so.dbg FORCE
> > +     $(call if_changed,objcopy)
> > +
> > +obj-y += vdso.o
> > +
> > +$(obj)/vdso.o : $(obj)/vdso.so
> > +
> > +# install commands for the unstripped file
> > +quiet_cmd_vdso_install = INSTALL $@
> > +      cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
> > +
> > +vdso.so: $(obj)/vdso.so.dbg
> > +     @mkdir -p $(MODLIB)/vdso
> > +     $(call cmd,vdso_install)
> > +
> > +vdso_install: vdso.so
> > diff --git a/arch/loongarch/vdso/elf.S b/arch/loongarch/vdso/elf.S
> > new file mode 100644
> > index 000000000000..9bb21b9f9583
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/elf.S
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#include <asm/vdso/vdso.h>
> > +
> > +#include <linux/elfnote.h>
> > +#include <linux/version.h>
> > +
> > +ELFNOTE_START(Linux, 0, "a")
> > +     .long LINUX_VERSION_CODE
> > +ELFNOTE_END
> > diff --git a/arch/loongarch/vdso/gen_vdso_offsets.sh b/arch/loongarch/vdso/gen_vdso_offsets.sh
> > new file mode 100755
> > index 000000000000..1bb4e12642ff
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/gen_vdso_offsets.sh
> > @@ -0,0 +1,13 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +
> > +#
> > +# Derived from RISC-V and ARM64:
> > +# Author: Will Deacon <will.deacon@arm.com>
> > +#
> > +# Match symbols in the DSO that look like VDSO_*; produce a header file
> > +# of constant offsets into the shared object.
> > +#
> > +
> > +LC_ALL=C sed -n -e 's/^00*/0/' -e \
> > +'s/^\([0-9a-fA-F]*\) . VDSO_\([a-zA-Z0-9_]*\)$/\#define vdso_offset_\2\t0x\1/p'
> > diff --git a/arch/loongarch/vdso/sigreturn.S b/arch/loongarch/vdso/sigreturn.S
> > new file mode 100644
> > index 000000000000..9cb3c58fad03
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/sigreturn.S
> > @@ -0,0 +1,24 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#include <asm/vdso/vdso.h>
> > +
> > +#include <linux/linkage.h>
> > +#include <uapi/asm/unistd.h>
> > +
> > +#include <asm/regdef.h>
> > +#include <asm/asm.h>
> > +
> > +     .section        .text
> > +     .cfi_sections   .debug_frame
> > +
> > +SYM_FUNC_START(__vdso_rt_sigreturn)
> > +
> > +     li.w    a7, __NR_rt_sigreturn
> > +     syscall 0
> > +
> > +SYM_FUNC_END(__vdso_rt_sigreturn)
> > diff --git a/arch/loongarch/vdso/vdso.S b/arch/loongarch/vdso/vdso.S
> > new file mode 100644
> > index 000000000000..46789bade6ff
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/vdso.S
> > @@ -0,0 +1,22 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + *
> > + * Derived from RISC-V:
> > + * Copyright (C) 2014 Regents of the University of California
> > + */
> > +
> > +#include <linux/init.h>
> > +#include <linux/linkage.h>
> > +#include <asm/page.h>
> > +
> > +     __PAGE_ALIGNED_DATA
> > +
> > +     .globl vdso_start, vdso_end
> > +     .balign PAGE_SIZE
> > +vdso_start:
> > +     .incbin "arch/loongarch/vdso/vdso.so"
> > +     .balign PAGE_SIZE
> > +vdso_end:
> > +
> > +     .previous
> > diff --git a/arch/loongarch/vdso/vdso.lds.S b/arch/loongarch/vdso/vdso.lds.S
> > new file mode 100644
> > index 000000000000..955f02de4a2d
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/vdso.lds.S
> > @@ -0,0 +1,72 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Author: Huacai Chen <chenhuacai@loongson.cn>
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +OUTPUT_FORMAT("elf64-loongarch", "elf64-loongarch", "elf64-loongarch")
> > +
> > +OUTPUT_ARCH(loongarch)
> > +
> > +SECTIONS
> > +{
> > +     PROVIDE(_start = .);
> > +     . = SIZEOF_HEADERS;
> > +
> > +     .hash           : { *(.hash) }                  :text
> > +     .gnu.hash       : { *(.gnu.hash) }
> > +     .dynsym         : { *(.dynsym) }
> > +     .dynstr         : { *(.dynstr) }
> > +     .gnu.version    : { *(.gnu.version) }
> > +     .gnu.version_d  : { *(.gnu.version_d) }
> > +     .gnu.version_r  : { *(.gnu.version_r) }
> > +
> > +     .note           : { *(.note.*) }                :text :note
> > +
> > +     .text           : { *(.text*) }                 :text
> > +     PROVIDE (__etext = .);
> > +     PROVIDE (_etext = .);
> > +     PROVIDE (etext = .);
> > +
> > +     .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text :eh_frame_hdr
> > +     .eh_frame       : { KEEP (*(.eh_frame)) }       :text
> > +
> > +     .dynamic        : { *(.dynamic) }               :text :dynamic
> > +
> > +     .rodata         : { *(.rodata*) }               :text
> > +
> > +     _end = .;
> > +     PROVIDE(end = .);
> > +
> > +     /DISCARD/       : {
> > +             *(.gnu.attributes)
> > +             *(.note.GNU-stack)
> > +             *(.data .data.* .gnu.linkonce.d.* .sdata*)
> > +             *(.bss .sbss .dynbss .dynsbss)
> > +     }
> > +}
> > +
> > +PHDRS
> > +{
> > +     text            PT_LOAD         FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
> > +     dynamic         PT_DYNAMIC      FLAGS(4);               /* PF_R */
> > +     note            PT_NOTE         FLAGS(4);               /* PF_R */
> > +     eh_frame_hdr    PT_GNU_EH_FRAME;
> > +}
> > +
> > +VERSION
> > +{
> > +     LINUX_5.10 {
> > +     global:
> > +             __vdso_clock_getres;
> > +             __vdso_clock_gettime;
> > +             __vdso_gettimeofday;
> > +             __vdso_rt_sigreturn;
> > +     local: *;
> > +     };
> > +}
> > +
> > +/*
> > + * Make the sigreturn code visible to the kernel.
> > + */
> > +VDSO_sigreturn               = __vdso_rt_sigreturn;
> > diff --git a/arch/loongarch/vdso/vgettimeofday.c b/arch/loongarch/vdso/vgettimeofday.c
> > new file mode 100644
> > index 000000000000..b1f4548dae92
> > --- /dev/null
> > +++ b/arch/loongarch/vdso/vgettimeofday.c
> > @@ -0,0 +1,25 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * LoongArch userspace implementations of gettimeofday() and similar.
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +#include <linux/types.h>
> > +
> > +int __vdso_clock_gettime(clockid_t clock,
> > +                      struct __kernel_timespec *ts)
> > +{
> > +     return __cvdso_clock_gettime(clock, ts);
> > +}
> > +
> > +int __vdso_gettimeofday(struct __kernel_old_timeval *tv,
> > +                     struct timezone *tz)
> > +{
> > +     return __cvdso_gettimeofday(tv, tz);
> > +}
> > +
> > +int __vdso_clock_getres(clockid_t clock_id,
> > +                     struct __kernel_timespec *res)
> > +{
> > +     return __cvdso_clock_getres(clock_id, res);
> > +}
>
> Other bits look familiar (it's generic vDSO but shows MIPS heritage
> too); from my experience with the MIPS vDSO this feels correct as well.
> Also I think an earlier version of the code is already deployed on my
> system and obviously working.
>
> The only minor nit is, the proper capitalization "VDSO" should be "vDSO"
> -- it's short for "virtual DSO" after all. But the all-caps "VDSO" also
> has many occurrences so I guess it's down to preferences. Either would
> be okay for me, although I'd personally prefer "vDSO".
>
> With the *other* bit (regarding asm constraints) addressed:
>
> Reviewed-by: WANG Xuerui <git@xen0n.name>
>