Date:   Fri, 17 Sep 2021 16:10:21 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Huacai Chen <chenhuacai@...ngson.cn>
Cc:     Arnd Bergmann <arnd@...db.de>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V3 14/22] LoongArch: Add signal handling support

Huacai Chen <chenhuacai@...ngson.cn> writes:

> This patch adds signal handling support for LoongArch.

My overall impression is that it looks like this code has a lot of
boilerplate code copied from mips that mips needs because of it's
long history, but that a fresh architecture should not need.

For example does LoongArch have a version without built in floating
point support?

To the best of my knowledge it has been decades since anyone built
a cpu capable of running Linux that doesn't have built in floating point
support.

Similarly this includes code for parameterize some of the userspace ABI.
Since you only have a single userspace ABI there should not need to be
any parameters.  So removing the unnecessary parameters should simplify
the code.

I have a few more comments inline along the same lines.

Eric

> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>  arch/loongarch/include/asm/abi.h             |  27 ++
>  arch/loongarch/include/uapi/asm/sigcontext.h |  40 ++
>  arch/loongarch/include/uapi/asm/ucontext.h   |  35 ++
>  arch/loongarch/kernel/signal-common.h        |  38 ++
>  arch/loongarch/kernel/signal.c               | 467 +++++++++++++++++++
>  5 files changed, 607 insertions(+)
>  create mode 100644 arch/loongarch/include/asm/abi.h
>  create mode 100644 arch/loongarch/include/uapi/asm/sigcontext.h
>  create mode 100644 arch/loongarch/include/uapi/asm/ucontext.h
>  create mode 100644 arch/loongarch/kernel/signal-common.h
>  create mode 100644 arch/loongarch/kernel/signal.c
>
> diff --git a/arch/loongarch/include/asm/abi.h b/arch/loongarch/include/asm/abi.h
> new file mode 100644
> index 000000000000..ced8534db4df
> --- /dev/null
> +++ b/arch/loongarch/include/asm/abi.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +#ifndef _ASM_ABI_H
> +#define _ASM_ABI_H
> +
> +#include <linux/signal_types.h>
> +
> +#include <asm/signal.h>
> +#include <asm/siginfo.h>
> +#include <asm/vdso.h>
> +
> +struct loongarch_abi {
> +	const unsigned long	restart;
> +	const int		audit_arch;
> +
> +	unsigned int off_sc_fpregs;
> +	unsigned int off_sc_fcc;
> +	unsigned int off_sc_fcsr;
> +	unsigned int off_sc_vcsr;
> +	unsigned int off_sc_flags;
> +
> +	struct loongarch_vdso_info *vdso;
> +};

This header file is confusing.  It says ABI but it isn't under the uapi
tree.  On mips with decades of history and a nabi, oabi, etc, the
similar header file which includes function pointers makes a smidgen of
sense.

Since you aren't mips and your architecture is new you should be able to
have a single userspace ABI and hard code everything.  At least to get
started with.

That should make for simpler code as well.

> +
> +#endif /* _ASM_ABI_H */
> diff --git a/arch/loongarch/include/uapi/asm/sigcontext.h b/arch/loongarch/include/uapi/asm/sigcontext.h
> new file mode 100644
> index 000000000000..da0e5bac2d80
> --- /dev/null
> +++ b/arch/loongarch/include/uapi/asm/sigcontext.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +/*
> + * Author: Hanlu Li <lihanlu@...ngson.cn>
> + *         Huacai Chen <chenhuacai@...ngson.cn>
> + *
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +#ifndef _UAPI_ASM_SIGCONTEXT_H
> +#define _UAPI_ASM_SIGCONTEXT_H
> +
> +#include <linux/types.h>
> +#include <asm/processor.h>
> +
> +/* scalar FP context was used */
> +#define USED_FP			(1 << 0)
> +
> +/* extended context was used, see struct extcontext for details */
> +#define USED_EXTCONTEXT		(1 << 1)
> +
> +#include <linux/posix_types.h>
> +/*
> + * Keep this struct definition in sync with the sigcontext fragment
> + * in arch/loongarch/kernel/asm-offsets.c

If this is uapi this can't change (except for consuming the reserved
fields).  Making this comment misleading.

> + *
> + */
> +struct sigcontext {
> +	__u64	sc_pc;
> +	__u64	sc_regs[32];
> +	__u32	sc_flags;
> +
> +	__u32	sc_fcsr;
> +	__u32	sc_vcsr;

You might want to document the 32bit hole in your structure here.

> +	__u64	sc_fcc;
> +	__u64	sc_scr[4];
> +
> +	union fpureg sc_fpregs[32] FPU_ALIGN;
> +	__u8	sc_reserved[4096] __attribute__((__aligned__(16)));
> +};
> +
> +#endif /* _UAPI_ASM_SIGCONTEXT_H */
> diff --git a/arch/loongarch/include/uapi/asm/ucontext.h b/arch/loongarch/include/uapi/asm/ucontext.h
> new file mode 100644
> index 000000000000..12577e22b1c7
> --- /dev/null
> +++ b/arch/loongarch/include/uapi/asm/ucontext.h
> @@ -0,0 +1,35 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef __LOONGARCH_UAPI_ASM_UCONTEXT_H
> +#define __LOONGARCH_UAPI_ASM_UCONTEXT_H
> +
> +/**
> + * struct ucontext - user context structure
> + * @uc_flags:
> + * @uc_link:
> + * @uc_stack:
> + * @uc_mcontext:	holds basic processor state
> + * @uc_sigmask:
> + * @uc_extcontext:	holds extended processor state
> + */
> +struct ucontext {
> +	unsigned long		uc_flags;
> +	struct ucontext		*uc_link;
> +	stack_t			uc_stack;
> +	sigset_t		uc_sigmask;
> +	/* There's some padding here to allow sigset_t to be expanded in the
> +	 * future.  Though this is unlikely, other architectures put uc_sigmask
> +	 * at the end of this structure and explicitly state it can be
> +	 * expanded, so we didn't want to box ourselves in here. */
> +	__u8		  __unused[1024 / 8 - sizeof(sigset_t)];
> +	/* We can't put uc_sigmask at the end of this structure because we need
> +	 * to be able to expand sigcontext in the future.  For example, the
> +	 * vector ISA extension will almost certainly add ISA state.  We want
> +	 * to ensure all user-visible ISA state can be saved and restored via a
> +	 * ucontext, so we're putting this at the end in order to allow for
> +	 * infinite extensibility.  Since we know this will be extended and we
> +	 * assume sigset_t won't be extended an extreme amount, we're
> +	 * prioritizing this. */
> +	struct sigcontext	uc_mcontext;
> +};
> +
> +#endif /* __LOONGARCH_UAPI_ASM_UCONTEXT_H */
> diff --git a/arch/loongarch/kernel/signal-common.h b/arch/loongarch/kernel/signal-common.h
> new file mode 100644
> index 000000000000..1693fbdedeaa
> --- /dev/null
> +++ b/arch/loongarch/kernel/signal-common.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Author: Hanlu Li <lihanlu@...ngson.cn>
> + *         Huacai Chen <chenhuacai@...ngson.cn>
> + *
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + */
> +
> +#ifndef __SIGNAL_COMMON_H
> +#define __SIGNAL_COMMON_H
> +
> +/* #define DEBUG_SIG */
> +
> +#ifdef DEBUG_SIG
> +#  define DEBUGP(fmt, args...) printk("%s: " fmt, __func__, ##args)
> +#else
> +#  define DEBUGP(fmt, args...)
> +#endif

This is only used once in arch/loongarch/kernel/signal.c
so you probably want to keep this define local to that file.

> +/*
> + * Determine which stack to use..
> + */
> +extern void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
> +				 size_t frame_size);
> +/* Check and clear pending FPU exceptions in saved CSR */
> +extern int fpcsr_pending(unsigned int __user *fpcsr);
> +
> +/* Make sure we will not lose FPU ownership */
> +#define lock_fpu_owner()	({ preempt_disable(); pagefault_disable(); })
> +#define unlock_fpu_owner()	({ pagefault_enable(); preempt_enable(); })
> +
> +/* Assembly functions to move context to/from the FPU */
> +extern asmlinkage int
> +_save_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
> +extern asmlinkage int
> +_restore_fp_context(void __user *fpregs, void __user *fcc, void __user *csr);
> +
> +#endif	/* __SIGNAL_COMMON_H */
> diff --git a/arch/loongarch/kernel/signal.c b/arch/loongarch/kernel/signal.c
> new file mode 100644
> index 000000000000..78319d2575c6
> --- /dev/null
> +++ b/arch/loongarch/kernel/signal.c
> @@ -0,0 +1,467 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Author: Hanlu Li <lihanlu@...ngson.cn>
> + *         Huacai Chen <chenhuacai@...ngson.cn>
> + * Copyright (C) 2020-2021 Loongson Technology Corporation Limited
> + *
> + * Derived from MIPS:
> + * Copyright (C) 1991, 1992  Linus Torvalds
> + * Copyright (C) 1994 - 2000  Ralf Baechle
> + * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
> + * Copyright (C) 2014, Imagination Technologies Ltd.
> + */
> +#include <linux/audit.h>
> +#include <linux/cache.h>
> +#include <linux/context_tracking.h>
> +#include <linux/irqflags.h>
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/personality.h>
> +#include <linux/smp.h>
> +#include <linux/kernel.h>
> +#include <linux/signal.h>
> +#include <linux/errno.h>
> +#include <linux/wait.h>
> +#include <linux/ptrace.h>
> +#include <linux/unistd.h>
> +#include <linux/uprobes.h>
> +#include <linux/compiler.h>
> +#include <linux/syscalls.h>
> +#include <linux/uaccess.h>
> +#include <linux/tracehook.h>
> +
> +#include <asm/abi.h>
> +#include <asm/asm.h>
> +#include <asm/cacheflush.h>
> +#include <asm/fpu.h>
> +#include <asm/ucontext.h>
> +#include <asm/cpu-features.h>
> +
> +#include "signal-common.h"
> +
> +static int (*save_fp_context)(void __user *sc);
> +static int (*restore_fp_context)(void __user *sc);
> +
> +struct rt_sigframe {
> +	struct siginfo rs_info;
> +	struct ucontext rs_uctx;
> +};
> +
> +/*
> + * Thread saved context copy to/from a signal context presumed to be on the
> + * user stack, and therefore accessed with appropriate macros from uaccess.h.
> + */
> +static int copy_fp_to_sigcontext(void __user *sc)
> +{
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint64_t __user *fcc = sc + abi->off_sc_fcc;
> +	uint32_t __user *csr = sc + abi->off_sc_fcsr;
> +	int i;
> +	int err = 0;
> +	int inc = 1;
> +
> +	for (i = 0; i < NUM_FPU_REGS; i += inc) {
> +		err |=
> +		    __put_user(get_fpr64(&current->thread.fpu.fpr[i], 0),
> +			       &fpregs[4*i]);
> +	}
> +	err |= __put_user(current->thread.fpu.fcsr, csr);
> +	err |= __put_user(current->thread.fpu.fcc, fcc);
> +
> +	return err;
> +}
> +
> +static int copy_fp_from_sigcontext(void __user *sc)
> +{
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint64_t __user *fcc = sc + abi->off_sc_fcc;
> +	uint32_t __user *csr = sc + abi->off_sc_fcsr;
> +	int i;
> +	int err = 0;
> +	int inc = 1;
> +	u64 fpr_val;
> +
> +	for (i = 0; i < NUM_FPU_REGS; i += inc) {
> +		err |= __get_user(fpr_val, &fpregs[4*i]);
> +		set_fpr64(&current->thread.fpu.fpr[i], 0, fpr_val);
> +	}
> +	err |= __get_user(current->thread.fpu.fcsr, csr);
> +	err |= __get_user(current->thread.fpu.fcc, fcc);
> +
> +	return err;
> +}
> +
> +/*
> + * Wrappers for the assembly _{save,restore}_fp_context functions.
> + */
> +static int save_hw_fp_context(void __user *sc)
> +{
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint64_t __user *fcc = sc + abi->off_sc_fcc;
> +	uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> +
> +	return _save_fp_context(fpregs, fcc, fcsr);
> +}
> +
> +static int restore_hw_fp_context(void __user *sc)
> +{
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint64_t __user *fcc = sc + abi->off_sc_fcc;
> +	uint32_t __user *csr = sc + abi->off_sc_fcsr;
> +
> +	return _restore_fp_context(fpregs, fcc, csr);
> +}
> +
> +/*
> + * Helper routines
> + */
> +static int protected_save_fp_context(void __user *sc)
> +{
> +	int err = 0;
> +	unsigned int used;
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint32_t __user *fcc = sc + abi->off_sc_fcsr;
> +	uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> +	uint32_t __user *vcsr = sc + abi->off_sc_vcsr;
> +	uint32_t __user *flags = sc + abi->off_sc_flags;
> +
> +	used = used_math() ? USED_FP : 0;
> +	if (!used)
> +		goto fp_done;
> +
> +	while (1) {
> +		lock_fpu_owner();
> +		if (is_fpu_owner())
> +			err = save_fp_context(sc);
> +		else
> +			err |= copy_fp_to_sigcontext(sc);
> +		unlock_fpu_owner();
> +		if (likely(!err))
> +			break;
> +		/* touch the sigcontext and try again */
> +		err = __put_user(0, &fpregs[0]) |
> +			__put_user(0, &fpregs[32*4 - 1]) |
> +			__put_user(0, fcc) |
> +			__put_user(0, fcsr) |
> +			__put_user(0, vcsr);
> +		if (err)
> +			return err;	/* really bad sigcontext */
> +	}
> +
> +fp_done:
> +	return __put_user(used, flags);
> +}
> +
> +static int protected_restore_fp_context(void __user *sc)
> +{
> +	unsigned int used;
> +	int err = 0, sig = 0, tmp __maybe_unused;
> +	struct loongarch_abi *abi = current->thread.abi;
> +	uint64_t __user *fpregs = sc + abi->off_sc_fpregs;
> +	uint32_t __user *fcsr = sc + abi->off_sc_fcsr;
> +	uint32_t __user *fcc = sc + abi->off_sc_fcsr;
> +	uint32_t __user *vcsr = sc + abi->off_sc_vcsr;
> +	uint32_t __user *flags = sc + abi->off_sc_flags;
> +
> +	err = __get_user(used, flags);
> +	conditional_used_math(used & USED_FP);
> +
> +	/*
> +	 * The signal handler may have used FPU; give it up if the program
> +	 * doesn't want it following sigreturn.
> +	 */
> +	if (err || !(used & USED_FP))
> +		lose_fpu(0);
> +
> +	if (err)
> +		return err;
> +
> +	if (!(used & USED_FP))
> +		goto fp_done;
> +
> +	err = sig = fpcsr_pending(fcsr);
> +	if (err < 0)
> +		return err;
> +
> +	while (1) {
> +		lock_fpu_owner();
> +		if (is_fpu_owner())
> +			err = restore_fp_context(sc);
> +		else
> +			err |= copy_fp_from_sigcontext(sc);
> +		unlock_fpu_owner();
> +		if (likely(!err))
> +			break;
> +		/* touch the sigcontext and try again */
> +		err = __get_user(tmp, &fpregs[0]) |
> +			__get_user(tmp, &fpregs[32*4 - 1]) |
> +			__get_user(tmp, fcc) |
> +			__get_user(tmp, fcsr) |
> +			__get_user(tmp, vcsr);
> +		if (err)
> +			break;	/* really bad sigcontext */
> +	}
> +
> +fp_done:
> +	return err ?: sig;
> +}
> +
> +static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
> +{
> +	int err = 0;
> +	int i;
> +
> +	err |= __put_user(regs->csr_epc, &sc->sc_pc);
> +
> +	err |= __put_user(0, &sc->sc_regs[0]);
> +	for (i = 1; i < 32; i++)
> +		err |= __put_user(regs->regs[i], &sc->sc_regs[i]);
> +
> +	/*
> +	 * Save FPU state to signal context. Signal handler
> +	 * will "inherit" current FPU state.
> +	 */
> +	err |= protected_save_fp_context(sc);
> +
> +	return err;
> +}
> +
> +int fpcsr_pending(unsigned int __user *fpcsr)
> +{
> +	int err, sig = 0;
> +	unsigned int csr, enabled;
> +
> +	err = __get_user(csr, fpcsr);
> +	enabled = ((csr & FPU_CSR_ALL_E) << 24);
> +	/*
> +	 * If the signal handler set some FPU exceptions, clear it and
> +	 * send SIGFPE.
> +	 */
> +	if (csr & enabled) {
> +		csr &= ~enabled;
> +		err |= __put_user(csr, fpcsr);
> +		sig = SIGFPE;
> +	}
> +	return err ?: sig;
> +}
> +
> +static int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
> +{
> +	int err = 0;
> +	int i;
> +
> +	/* Always make any pending restarted system calls return -EINTR */
> +	current->restart_block.fn = do_no_restart_syscall;
> +
> +	err |= __get_user(regs->csr_epc, &sc->sc_pc);
> +
> +	for (i = 1; i < 32; i++)
> +		err |= __get_user(regs->regs[i], &sc->sc_regs[i]);
> +
> +	return err ?: protected_restore_fp_context(sc);
> +}
> +
> +void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
> +			  size_t frame_size)
> +{
> +	unsigned long sp;
> +
> +	/* Default to using normal stack */
> +	sp = regs->regs[3];
> +	sp -= 32;   /* Reserve 32-bytes. */
> +
> +	sp = sigsp(sp, ksig);
> +
> +	return (void __user *)((sp - frame_size) & ALMASK);
> +}
> +
> +/*
> + * Atomically swap in the new signal mask, and wait for a signal.
> + */
> +
> +asmlinkage long sys_rt_sigreturn(void)
> +{
> +	struct rt_sigframe __user *frame;
> +	struct pt_regs *regs;
> +	sigset_t set;
> +	int sig;
> +
> +	regs = current_pt_regs();
> +	frame = (struct rt_sigframe __user *)regs->regs[3];
> +	if (!access_ok(frame, sizeof(*frame)))
> +		goto badframe;
> +	if (__copy_from_user(&set, &frame->rs_uctx.uc_sigmask, sizeof(set)))
> +		goto badframe;
> +
> +	set_current_blocked(&set);
> +
> +	sig = restore_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
> +	if (sig < 0)
> +		goto badframe;
> +	else if (sig)
> +		force_sig(sig);
> +
> +	if (restore_altstack(&frame->rs_uctx.uc_stack))
> +		goto badframe;
> +
> +	return regs->regs[4];
> +
> +badframe:
> +	force_sig(SIGSEGV);
> +	return 0;
> +}
> +
> +static int setup_rt_frame(void *sig_return, struct ksignal *ksig,
> +			  struct pt_regs *regs, sigset_t *set)
> +{
> +	struct rt_sigframe __user *frame;
> +	int err = 0;
> +
> +	frame = get_sigframe(ksig, regs, sizeof(*frame));
> +	if (!access_ok(frame, sizeof(*frame)))
> +		return -EFAULT;
> +
> +	/* Create siginfo.  */
> +	err |= copy_siginfo_to_user(&frame->rs_info, &ksig->info);
> +
> +	/* Create the ucontext.	 */
> +	err |= __put_user(0, &frame->rs_uctx.uc_flags);
> +	err |= __put_user(NULL, &frame->rs_uctx.uc_link);
> +	err |= __save_altstack(&frame->rs_uctx.uc_stack, regs->regs[3]);
> +	err |= setup_sigcontext(regs, &frame->rs_uctx.uc_mcontext);
> +	err |= __copy_to_user(&frame->rs_uctx.uc_sigmask, set, sizeof(*set));
> +
> +	if (err)
> +		return -EFAULT;
> +
> +	/*
> +	 * Arguments to signal handler:
> +	 *
> +	 *   a0 = signal number
> +	 *   a1 = 0 (should be cause)
> +	 *   a2 = pointer to ucontext
> +	 *
> +	 * $25 and c0_epc point to the signal handler, $29 points to
> +	 * the struct rt_sigframe.
> +	 */
> +	regs->regs[4] = ksig->sig;
> +	regs->regs[5] = (unsigned long) &frame->rs_info;
> +	regs->regs[6] = (unsigned long) &frame->rs_uctx;
> +	regs->regs[3] = (unsigned long) frame;
> +	regs->regs[1] = (unsigned long) sig_return;
> +	regs->csr_epc = (unsigned long) ksig->ka.sa.sa_handler;
> +
> +	DEBUGP("SIG deliver (%s:%d): sp=0x%p pc=0x%lx ra=0x%lx\n",
> +	       current->comm, current->pid,
> +	       frame, regs->csr_epc, regs->regs[1]);
> +
> +	return 0;
> +}
> +
> +struct loongarch_abi loongarch_abi = {
> +	.restart	= __NR_restart_syscall,
> +#ifdef CONFIG_32BIT
> +	.audit_arch	= AUDIT_ARCH_LOONGARCH32,
> +#else
> +	.audit_arch	= AUDIT_ARCH_LOONGARCH64,
> +#endif
> +
> +	.off_sc_fpregs	= offsetof(struct sigcontext, sc_fpregs),
> +	.off_sc_fcc	= offsetof(struct sigcontext, sc_fcc),
> +	.off_sc_fcsr	= offsetof(struct sigcontext, sc_fcsr),
> +	.off_sc_vcsr	= offsetof(struct sigcontext, sc_vcsr),
> +	.off_sc_flags	= offsetof(struct sigcontext, sc_flags),
> +
> +	.vdso		= &vdso_info,
> +};
> +
> +static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
> +{
> +	int ret;
> +	sigset_t *oldset = sigmask_to_save();
> +	struct loongarch_abi *abi = current->thread.abi;
> +	void *vdso = current->mm->context.vdso;
> +
> +	/* Are we from a system call? */
> +	if (regs->regs[0]) {
> +		switch (regs->regs[4]) {
> +		case -ERESTART_RESTARTBLOCK:
> +		case -ERESTARTNOHAND:
> +			regs->regs[4] = -EINTR;
> +			break;
> +		case -ERESTARTSYS:
> +			if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
> +				regs->regs[4] = -EINTR;
> +				break;
> +			}
> +			fallthrough;
> +		case -ERESTARTNOINTR:
> +			regs->regs[4] = regs->orig_a0;
> +			regs->csr_epc -= 4;
> +		}
> +
> +		regs->regs[0] = 0;	/* Don't deal with this again.	*/
> +	}
> +
> +	rseq_signal_deliver(ksig, regs);
> +
> +	ret = setup_rt_frame(vdso + abi->vdso->offset_sigreturn, ksig, regs, oldset);
> +
> +	signal_setup_done(ret, ksig, 0);
> +}
> +
> +void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
> +{
> +	struct ksignal ksig;
> +
> +	if (has_signal && get_signal(&ksig)) {
> +		/* Whee!  Actually deliver the signal.	*/
> +		handle_signal(&ksig, regs);
> +		return;
> +	}
> +
> +	/* Are we from a system call? */
> +	if (regs->regs[0]) {
> +		switch (regs->regs[4]) {
> +		case -ERESTARTNOHAND:
> +		case -ERESTARTSYS:
> +		case -ERESTARTNOINTR:
> +			regs->regs[4] = regs->orig_a0;
> +			regs->csr_epc -= 4;
> +			break;
> +
> +		case -ERESTART_RESTARTBLOCK:
> +			regs->regs[4] = regs->orig_a0;
> +			regs->regs[11] = current->thread.abi->restart;
> +			regs->csr_epc -= 4;
> +			break;
> +		}
> +		regs->regs[0] = 0;	/* Don't deal with this again.	*/
> +	}
> +
> +	/*
> +	 * If there's no signal to deliver, we just put the saved sigmask
> +	 * back
> +	 */
> +	restore_saved_sigmask();
> +}
> +
> +static int signal_setup(void)
> +{
> +	if (cpu_has_fpu) {
> +		save_fp_context = save_hw_fp_context;
> +		restore_fp_context = restore_hw_fp_context;
> +	} else {
> +		save_fp_context = copy_fp_to_sigcontext;
> +		restore_fp_context = copy_fp_from_sigcontext;
> +	}
> +
> +	return 0;
> +}
> +
> +arch_initcall(signal_setup);

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