safe-syscall.inc.S (2939B)
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 linux-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 * We return a long which is the syscall's return value, which 26 * may be negative-errno on failure. Conversion to the 27 * -1-and-errno-set convention is done by the calling wrapper. 28 */ 29#if _CALL_ELF == 2 30safe_syscall_base: 31 .cfi_startproc 32 .localentry safe_syscall_base,0 33#else 34 .section ".opd","aw" 35 .align 3 36safe_syscall_base: 37 .quad .L.safe_syscall_base,.TOC.@tocbase,0 38 .previous 39.L.safe_syscall_base: 40 .cfi_startproc 41#endif 42 /* We enter with r3 == *signal_pending 43 * r4 == syscall number 44 * r5 ... r10 == syscall arguments 45 * and return the result in r3 46 * and the syscall instruction needs 47 * r0 == syscall number 48 * r3 ... r8 == syscall arguments 49 * and returns the result in r3 50 * Shuffle everything around appropriately. 51 */ 52 std 14, 16(1) /* Preserve r14 in SP+16 */ 53 .cfi_offset 14, 16 54 mr 14, 3 /* signal_pending */ 55 mr 0, 4 /* syscall number */ 56 mr 3, 5 /* syscall arguments */ 57 mr 4, 6 58 mr 5, 7 59 mr 6, 8 60 mr 7, 9 61 mr 8, 10 62 63 /* This next sequence of code works in conjunction with the 64 * rewind_if_safe_syscall_function(). If a signal is taken 65 * and the interrupted PC is anywhere between 'safe_syscall_start' 66 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 67 * The code sequence must therefore be able to cope with this, and 68 * the syscall instruction must be the final one in the sequence. 69 */ 70safe_syscall_start: 71 /* if signal_pending is non-zero, don't do the call */ 72 lwz 12, 0(14) 73 cmpwi 0, 12, 0 74 bne- 0f 75 sc 76safe_syscall_end: 77 /* code path when we did execute the syscall */ 78 ld 14, 16(1) /* restore r14 to its original value */ 79 bnslr+ 80 81 /* syscall failed; return negative errno */ 82 neg 3, 3 83 blr 84 85 /* code path when we didn't execute the syscall */ 860: addi 3, 0, -TARGET_ERESTARTSYS 87 ld 14, 16(1) /* restore r14 to its original value */ 88 blr 89 .cfi_endproc 90 91#if _CALL_ELF == 2 92 .size safe_syscall_base, .-safe_syscall_base 93#else 94 .size safe_syscall_base, .-.L.safe_syscall_base 95 .size .L.safe_syscall_base, .-.L.safe_syscall_base 96#endif