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Message-ID: <5b14144a-9725-41db-7179-c059c41814cf@xen0n.name>
Date:   Sun, 15 May 2022 22:47:16 +0800
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Subject: Re: [PATCH V10 19/22] LoongArch: Add VDSO and VSYSCALL support
To:     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>
Cc:     linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xuefeng Li <lixuefeng@loongson.cn>,
        Yanteng Si <siyanteng@loongson.cn>,
        Huacai Chen <chenhuacai@gmail.com>,
        Guo Ren <guoren@kernel.org>, Xuerui Wang <kernel@xen0n.name>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
References: <20220514080402.2650181-1-chenhuacai@loongson.cn>
 <20220514080402.2650181-20-chenhuacai@loongson.cn>
Content-Language: en-US
From:   WANG Xuerui <kernel@xen0n.name>
In-Reply-To: <20220514080402.2650181-20-chenhuacai@loongson.cn>
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Precedence: bulk

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 
$a0 from being clobbered before the syscall insn? Changing "v0" to "a0", 
then "=r" to "+r", could do it, although I cannot build-test it (due to 
the boot protocol being incompatible with existing shipped systems). 
Please check this for me...
> +
> +	return ret;
> +}
> +
> +static __always_inline long clock_gettime_fallback(
> +					clockid_t _clkid,
> +					struct __kernel_timespec *_ts)
> +{
> +	register clockid_t clkid asm("a0") = _clkid;
> +	register struct __kernel_timespec *ts asm("a1") = _ts;
> +	register long nr asm("a7") = __NR_clock_gettime;
> +	register long ret asm("v0");
> +
> +	asm volatile(
> +	"       syscall 0\n"
> +	: "=r" (ret)
> +	: "r" (nr), "r" (clkid), "r" (ts)
> +	: "$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>