safe-syscall.inc.S (3298B)
1 /* 2 * safe-syscall.inc.S : host-specific assembly fragment 3 * to handle signals occurring at the same time as system calls. 4 * This is intended to be included by common-user/safe-syscall.S 5 * 6 * Written by Richard Henderson <rth@twiddle.net> 7 * Copyright (C) 2016 Red Hat, Inc. 8 * 9 * This work is licensed under the terms of the GNU GPL, version 2 or later. 10 * See the COPYING file in the top-level directory. 11 */ 12 13 .global safe_syscall_base 14 .global safe_syscall_start 15 .global safe_syscall_end 16 .type safe_syscall_base, @function 17 18 .text 19 20 /* This is the entry point for making a system call. The calling 21 * convention here is that of a C varargs function with the 22 * first argument an 'int *' to the signal_pending flag, the 23 * second one the system call number (as a 'long'), and all further 24 * arguments being syscall arguments (also 'long'). 25 */ 26 #if _CALL_ELF == 2 27 safe_syscall_base: 28 .cfi_startproc 29 .localentry safe_syscall_base,0 30 #else 31 .section ".opd","aw" 32 .align 3 33 safe_syscall_base: 34 .quad .L.safe_syscall_base,.TOC.@tocbase,0 35 .previous 36 .L.safe_syscall_base: 37 .cfi_startproc 38 #endif 39 /* We enter with r3 == &signal_pending 40 * r4 == syscall number 41 * r5 ... r10 == syscall arguments 42 * and return the result in r3 43 * and the syscall instruction needs 44 * r0 == syscall number 45 * r3 ... r8 == syscall arguments 46 * and returns the result in r3 47 * Shuffle everything around appropriately. 48 */ 49 std 14, 16(1) /* Preserve r14 in SP+16 */ 50 .cfi_offset 14, 16 51 mr 14, 3 /* signal_pending */ 52 mr 0, 4 /* syscall number */ 53 mr 3, 5 /* syscall arguments */ 54 mr 4, 6 55 mr 5, 7 56 mr 6, 8 57 mr 7, 9 58 mr 8, 10 59 60 /* This next sequence of code works in conjunction with the 61 * rewind_if_safe_syscall_function(). If a signal is taken 62 * and the interrupted PC is anywhere between 'safe_syscall_start' 63 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 64 * The code sequence must therefore be able to cope with this, and 65 * the syscall instruction must be the final one in the sequence. 66 */ 67 safe_syscall_start: 68 /* if signal_pending is non-zero, don't do the call */ 69 lwz 12, 0(14) 70 cmpwi 0, 12, 0 71 bne- 2f 72 sc 73 safe_syscall_end: 74 /* code path when we did execute the syscall */ 75 ld 14, 16(1) /* restore r14 */ 76 bso- 1f 77 blr 78 79 /* code path when we didn't execute the syscall */ 80 2: ld 14, 16(1) /* restore r14 */ 81 addi 3, 0, QEMU_ERESTARTSYS 82 83 /* code path setting errno */ 84 1: b safe_syscall_set_errno_tail 85 nop /* per abi, for the linker to modify */ 86 87 .cfi_endproc 88 89 #if _CALL_ELF == 2 90 .size safe_syscall_base, .-safe_syscall_base 91 #else 92 .size safe_syscall_base, .-.L.safe_syscall_base 93 .size .L.safe_syscall_base, .-.L.safe_syscall_base 94 #endif