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+/*
+ * 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
+ *
+ * Copyright (C) 2022 Linaro, Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+/*
+ * Standardize on the _CALL_FOO symbols used by GCC:
+ * Apple XCode does not define _CALL_DARWIN.
+ * Clang defines _CALL_ELF (64-bit) but not _CALL_SYSV (32-bit).
+ */
+#if !defined(_CALL_SYSV) && \
+ !defined(_CALL_DARWIN) && \
+ !defined(_CALL_AIX) && \
+ !defined(_CALL_ELF)
+# if defined(__APPLE__)
+# define _CALL_DARWIN
+# elif defined(__ELF__) && TCG_TARGET_REG_BITS == 32
+# define _CALL_SYSV
+# else
+# error "Unknown ABI"
+# endif
+#endif
+
+#ifndef _CALL_SYSV
+# error "Unsupported ABI"
+#endif
+
+
+ .global safe_syscall_base
+ .global safe_syscall_start
+ .global safe_syscall_end
+ .type safe_syscall_base, @function
+
+ .text
+
+ /*
+ * 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
+ stwu 1, -8(1)
+ .cfi_def_cfa_offset 8
+ stw 30, 4(1)
+ .cfi_offset 30, -4
+
+ /*
+ * We enter with r3 == &signal_pending
+ * r4 == syscall number
+ * r5 ... r10 == syscall arguments
+ * and return the result in r3
+ * and the syscall instruction needs
+ * r0 == syscall number
+ * r3 ... r8 == syscall arguments
+ * and returns the result in r3
+ * Shuffle everything around appropriately.
+ */
+ mr 30, 3 /* signal_pending */
+ mr 0, 4 /* syscall number */
+ mr 3, 5 /* syscall arguments */
+ mr 4, 6
+ mr 5, 7
+ mr 6, 8
+ mr 7, 9
+ mr 8, 10
+
+ /*
+ * 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 */
+ lwz 12, 0(30)
+ cmpwi 0, 12, 0
+ bne- 2f
+ sc
+safe_syscall_end:
+ /* code path when we did execute the syscall */
+ lwz 30, 4(1) /* restore r30 */
+ addi 1, 1, 8 /* restore stack */
+ .cfi_restore 30
+ .cfi_def_cfa_offset 0
+ bnslr+ /* return on success */
+ b safe_syscall_set_errno_tail
+
+ /* code path when we didn't execute the syscall */
+2: lwz 30, 4(1)
+ addi 1, 1, 8
+ addi 3, 0, QEMU_ERESTARTSYS
+ b safe_syscall_set_errno_tail
+
+ .cfi_endproc
+
+ .size safe_syscall_base, .-safe_syscall_base