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| -rw-r--r-- | common-user/host/loongarch64/safe-syscall.inc.S | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/common-user/host/loongarch64/safe-syscall.inc.S b/common-user/host/loongarch64/safe-syscall.inc.S new file mode 100644 index 0000000000..b88a069c45 --- /dev/null +++ b/common-user/host/loongarch64/safe-syscall.inc.S @@ -0,0 +1,90 @@ +/* + * 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 + * + * Ported to LoongArch by WANG Xuerui <git@xen0n.name> + * + * Based on safe-syscall.inc.S code for RISC-V, + * originally 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. + */ + move $t0, $a0 /* signal_pending pointer */ + move $t1, $a1 /* syscall number */ + move $a0, $a2 /* syscall arguments */ + move $a1, $a3 + move $a2, $a4 + move $a3, $a5 + move $a4, $a6 + move $a5, $a7 + move $a7, $t1 + + /* + * We need to preserve the signal_pending pointer but t0 is + * clobbered by syscalls on LoongArch, so we need to move it + * somewhere else, ideally both preserved across syscalls and + * clobbered by procedure calls so we don't have to allocate a + * stack frame; a6 is just the register we want here. + */ + move $a6, $t0 + + /* + * 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 */ + ld.w $t1, $a6, 0 + bnez $t1, 2f + syscall 0 +safe_syscall_end: + /* code path for having successfully executed the syscall */ + li.w $t2, -4096 + bgtu $a0, $t2, 0f + jr $ra + + /* code path setting errno */ +0: sub.d $a0, $zero, $a0 + b safe_syscall_set_errno_tail + + /* code path when we didn't execute the syscall */ +2: li.w $a0, QEMU_ERESTARTSYS + b safe_syscall_set_errno_tail + .cfi_endproc + .size safe_syscall_base, .-safe_syscall_base |