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Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch6
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64 |
Date: |
Mon, 13 Jun 2016 23:04:16 +0100 |
On 13 June 2016 at 22:45, Richard Henderson <address@hidden> wrote:
> Signed-off-by: Richard Henderson <address@hidden>
> ---
> linux-user/host/aarch64/hostdep.h | 34 ++++++++++++++
> linux-user/host/aarch64/safe-syscall.inc.S | 72
> ++++++++++++++++++++++++++++++
> 2 files changed, 106 insertions(+)
> create mode 100644 linux-user/host/aarch64/hostdep.h
> create mode 100644 linux-user/host/aarch64/safe-syscall.inc.S
>
> diff --git a/linux-user/host/aarch64/hostdep.h
> b/linux-user/host/aarch64/hostdep.h
> new file mode 100644
> index 0000000..0ff7985
> --- /dev/null
> +++ b/linux-user/host/aarch64/hostdep.h
> @@ -0,0 +1,34 @@
> +/*
> + * hostdep.h : things which are dependent on the host architecture
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#ifndef QEMU_HOSTDEP_H
> +#define QEMU_HOSTDEP_H
> +
> +/* We have a safe-syscall.inc.S */
> +#define HAVE_SAFE_SYSCALL
> +
> +#ifndef __ASSEMBLER__
> +
> +/* These are defined by the safe-syscall.inc.S file */
> +extern char safe_syscall_start[];
> +extern char safe_syscall_end[];
> +
> +/* Adjust the signal context to rewind out of safe-syscall if we're in it */
> +static inline void rewind_if_in_safe_syscall(void *puc)
> +{
> + struct ucontext *uc = puc;
> + __u64 *pcreg = &uc->uc_mcontext.pc;
> +
> + if (*pcreg > (uintptr_t)safe_syscall_start
> + && *pcreg < (uintptr_t)safe_syscall_end) {
> + *pcreg = (uintptr_t)safe_syscall_start;
> + }
> +}
> +
> +#endif /* __ASSEMBLER__ */
> +
> +#endif
> diff --git a/linux-user/host/aarch64/safe-syscall.inc.S
> b/linux-user/host/aarch64/safe-syscall.inc.S
> new file mode 100644
> index 0000000..5416b90
> --- /dev/null
> +++ b/linux-user/host/aarch64/safe-syscall.inc.S
> @@ -0,0 +1,72 @@
> +/*
> + * 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
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> + .global safe_syscall_base
> + .global safe_syscall_start
> + .global safe_syscall_end
> + .type safe_syscall_base, #function
> + .type safe_syscall_start, #function
> + .type safe_syscall_end, #function
_start and _end aren't function entry points, so is it OK
to mark them as functions?
(The 'as' manual doesn't document what setting .type does in much
detail...)
> +
> + /* 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').
> + * We return a long which is the syscall's return value, which
> + * may be negative-errno on failure. Conversion to the
> + * -1-and-errno-set convention is done by the calling wrapper.
> + */
> +safe_syscall_base:
> + .cfi_startproc
> + /* The syscall calling convention isn't the same as the
> + * C one:
> + * we enter with x0 == *signal_pending
> + * x1 == syscall number
> + * x2 ... x7, (stack) == syscall arguments
> + * and return the result in x0
> + * and the syscall instruction needs
> + * x8 == syscall number
> + * x0 ... x6 == syscall arguments
> + * and returns the result in x0
> + * Shuffle everything around appropriately.
> + */
http://man7.org/linux/man-pages/man2/syscall.2.html
doesn't mention a syscall argument in x7, just x0..x5.
> + mov x9, x0 /* signal_pending pointer */
> + mov w8, w1 /* syscall number */
Seems a bit odd to use a 32-bit move for this when our input
calling convention has it as 64 bits and the kernel's calling
convention has it as 64 bits.
> + mov x0, x2 /* syscall arguments */
> + mov x1, x3
> + mov x2, x4
> + mov x3, x5
> + mov x4, x6
> + mov x6, x7
> + ldr x7, [sp]
> +
> + /* 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 */
> + ldr w10, [x9]
> + cbnz w10, 0f
> + svc 0x0
> +safe_syscall_end:
> + /* code path for having successfully executed the syscall */
> + ret
> +
> +0:
> + /* code path when we didn't execute the syscall */
> + mov x0, #-TARGET_ERESTARTSYS
> + ret
> + .cfi_endproc
> +
> + .size safe_syscall_base, .-safe_syscall_base
> --
> 2.5.5
>
thanks
-- PMM
- Re: [Qemu-devel] [PATCH 1/6] linux-user: fix x86_64 safe_syscall, (continued)
- [Qemu-devel] [PATCH 6/6] linux-user: Provide safe_syscall for ppc64, Richard Henderson, 2016/06/13
- [Qemu-devel] [PATCH 3/6] linux-user: Provide safe_syscall for arm, Richard Henderson, 2016/06/13
- [Qemu-devel] [PATCH 2/6] linux-user: Provide safe_syscall for i386, Richard Henderson, 2016/06/13
- [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Richard Henderson, 2016/06/13
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64,
Peter Maydell <=
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Richard Henderson, 2016/06/13
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Peter Maydell, 2016/06/13
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Peter Maydell, 2016/06/13
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Richard Henderson, 2016/06/13
- Re: [Qemu-devel] [PATCH 4/6] linux-user: Provide safe_syscall for aarch64, Peter Maydell, 2016/06/13
Re: [Qemu-devel] [PATCH 0/6] linux-user: safe_syscall updates, Peter Maydell, 2016/06/13