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Diffstat (limited to 'common-user/host/riscv/safe-syscall.inc.S')
| -rw-r--r-- | common-user/host/riscv/safe-syscall.inc.S | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/common-user/host/riscv/safe-syscall.inc.S b/common-user/host/riscv/safe-syscall.inc.S new file mode 100644 index 0000000000..dfe83c300e --- /dev/null +++ b/common-user/host/riscv/safe-syscall.inc.S @@ -0,0 +1,79 @@ +/* + * 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 common-user/safe-syscall.S + * + * Written by Richard Henderson <rth@twiddle.net> + * Copyright (C) 2018 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. + */ + + .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 + + /* + * 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'). + */ +safe_syscall_base: + .cfi_startproc + /* + * The syscall calling convention is nearly the same as C: + * we enter with a0 == &signal_pending + * a1 == syscall number + * a2 ... a7 == syscall arguments + * and return the result in a0 + * and the syscall instruction needs + * a7 == syscall number + * a0 ... a5 == syscall arguments + * and returns the result in a0 + * Shuffle everything around appropriately. + */ + mv t0, a0 /* signal_pending pointer */ + mv t1, a1 /* syscall number */ + mv a0, a2 /* syscall arguments */ + mv a1, a3 + mv a2, a4 + mv a3, a5 + mv a4, a6 + mv a5, a7 + mv a7, t1 + + /* + * 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, 2f + scall +safe_syscall_end: + /* code path for having successfully executed the syscall */ + li t2, -4096 + bgtu a0, t2, 0f + ret + + /* code path setting errno */ +0: neg a0, a0 + j safe_syscall_set_errno_tail + + /* code path when we didn't execute the syscall */ +2: li a0, QEMU_ERESTARTSYS + j safe_syscall_set_errno_tail + + .cfi_endproc + .size safe_syscall_base, .-safe_syscall_base |