On Wed, Nov 17, 2021 at 9:04 AM Richard Henderson <
richard.henderson@linaro.org> wrote:
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> common-user/host/mips/hostdep.h | 2 +
> common-user/host/mips/safe-syscall.inc.S | 135 +++++++++++++++++++++++
> 2 files changed, 137 insertions(+)
> create mode 100644 common-user/host/mips/hostdep.h
> create mode 100644 common-user/host/mips/safe-syscall.inc.S
>
Reviewed-by: Warner Losh <imp@bsdimp.com>
> diff --git a/common-user/host/mips/hostdep.h
> b/common-user/host/mips/hostdep.h
> new file mode 100644
> index 0000000000..b18aca1deb
> --- /dev/null
> +++ b/common-user/host/mips/hostdep.h
> @@ -0,0 +1,2 @@
> +/* We have a safe-syscall.inc.S */
> +#define HAVE_SAFE_SYSCALL
> diff --git a/common-user/host/mips/safe-syscall.inc.S
> b/common-user/host/mips/safe-syscall.inc.S
> new file mode 100644
> index 0000000000..1e2f5a079c
> --- /dev/null
> +++ b/common-user/host/mips/safe-syscall.inc.S
> @@ -0,0 +1,135 @@
> +/*
> + * safe-syscall.inc.S : host-specific assembly fragment
> + * to handle signals occurring at the same time as system calls.
> + * This is intended to be included by linux-user/safe-syscall.S
> + *
> + * Written by Richard Henderson <rth@twiddle.net>
> + * Copyright (C) 2021 Linaro, Inc.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "sys/regdef.h"
> +#include "sys/asm.h"
> +
> + .text
> + .set nomips16
> + .set noreorder
> +
> + .global safe_syscall_start
> + .global safe_syscall_end
> + .type safe_syscall_start, @function
> + .type safe_syscall_end, @function
> +
> + /*
> + * This is the entry point for making a system call. The calling
> + * convention here is that of a C varargs function with the
> + * first argument an 'int *' to the signal_pending flag, the
> + * second one the system call number (as a 'long'), and all further
> + * arguments being syscall arguments (also 'long').
> + */
> +
> +#if _MIPS_SIM == _ABIO32
> +/* Do not allocate a stack frame and store into the parameter space. */
> +#define FRAME 0
> +#define ERRNOP 4
> +#else
> +/* Allocate a stack frame and store into the first allocated slot. */
> +#define FRAME 16
> +#define ERRNOP 0
> +#endif
> +
> +NESTED(safe_syscall_base, FRAME, ra)
> + .cfi_startproc
> +#if _MIPS_SIM == _ABIO32
> + /*
> + * The syscall calling convention is nearly the same as C:
> + * we enter with a0 == &signal_pending
> + * a1 == &errno
> + * a2 == syscall number
> + * a3, stack == syscall arguments
> + * and return the result in a0
> + * and the syscall instruction needs
> + * v0 == syscall number
> + * a0 ... a3, stack == syscall arguments
> + * and returns the result in v0
> + * Shuffle everything around appropriately.
> + */
> + move t0, a0 /* signal_pending pointer */
> + sw a1, ERRNOP(sp) /* errno pointer */
> + move v0, a2 /* syscall number */
> + move a0, a3 /* syscall arguments */
> + lw a1, 16(sp)
> + lw a2, 20(sp)
> + lw a3, 24(sp)
> + lw t4, 28(sp)
> + lw t5, 32(sp)
> + lw t6, 40(sp)
> + lw t7, 44(sp)
> + sw t4, 16(sp)
> + sw t5, 20(sp)
> + sw t6, 24(sp)
> + sw t7, 28(sp)
> +#else
> + PTR_ADDIU sp, sp, -FRAME
> + .cfi_adjust_cfa_offset FRAME
> +
> + /*
> + * The syscall calling convention is nearly the same as C:
> + * we enter with a0 == &signal_pending
> + * a1 == &errno
> + * a2 == syscall number
> + * a3 ... a7, stack == syscall arguments
> + * and return the result in a0
> + * and the syscall instruction needs
> + * v0 == syscall number
> + * a0 ... a5 == syscall arguments
> + * and returns the result in v0
> + * Shuffle everything around appropriately.
> + */
> + move t0, a0 /* signal_pending pointer */
> + PTR_S a1, ERRNOP(sp) /* save errno pointer */
> + move v0, a2 /* syscall number */
> + move a0, a3 /* syscall arguments */
> + move a1, a4
> + move a2, a5
> + move a3, a6
> + move a4, a7
> + ld a5, 16(sp)
> +#endif
> +
> + /*
> + * This next sequence of code works in conjunction with the
> + * rewind_if_safe_syscall_function(). If a signal is taken
> + * and the interrupted PC is anywhere between 'safe_syscall_start'
> + * and 'safe_syscall_end' then we rewind it to
> 'safe_syscall_start'.
> + * The code sequence must therefore be able to cope with this, and
> + * the syscall instruction must be the final one in the sequence.
> + */
> +safe_syscall_start:
> + /* If signal_pending is non-zero, don't do the call */
> + lw t1, 0(t0)
> + bnez t1, 0f
> + nop
> + syscall
> +safe_syscall_end:
> +
> + /* code path for having successfully executed the syscall */
> + bnez a3, 1f
> + nop
> + jr ra
> + PTR_ADDIU sp, sp, FRAME
> +
> + /* code path when we didn't execute the syscall */
> +0: li v0, TARGET_ERESTARTSYS
> +
> + /* code path setting errno */
> +1: PTR_L t0, ERRNOP(sp)
> + sw v0, 0(t0) /* store errno */
> + li v0, -1
> + jr ra
> + PTR_ADDIU sp, sp, FRAME
> +
> + .cfi_endproc
> +END(safe_syscall_base)
> --
> 2.25.1
>
>