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 .cfi_sections .debug_frame 19 20 .text 21 .syntax unified 22 .arm 23 .align 2 24 25 /* This is the entry point for making a system call. The calling 26 * convention here is that of a C varargs function with the 27 * first argument an 'int *' to the signal_pending flag, the 28 * second one the system call number (as a 'long'), and all further 29 * arguments being syscall arguments (also 'long'). 30 * We return a long which is the syscall's return value, which 31 * may be negative-errno on failure. Conversion to the 32 * -1-and-errno-set convention is done by the calling wrapper. 33 */ 34safe_syscall_base: 35 .fnstart 36 .cfi_startproc 37 mov r12, sp /* save entry stack */ 38 push { r4, r5, r6, r7, r8, lr } 39 .save { r4, r5, r6, r7, r8, lr } 40 .cfi_adjust_cfa_offset 24 41 .cfi_rel_offset r4, 0 42 .cfi_rel_offset r5, 4 43 .cfi_rel_offset r6, 8 44 .cfi_rel_offset r7, 12 45 .cfi_rel_offset r8, 16 46 .cfi_rel_offset lr, 20 47 48 /* The syscall calling convention isn't the same as the C one: 49 * we enter with r0 == *signal_pending 50 * r1 == syscall number 51 * r2, r3, [sp+0] ... [sp+12] == syscall arguments 52 * and return the result in r0 53 * and the syscall instruction needs 54 * r7 == syscall number 55 * r0 ... r6 == syscall arguments 56 * and returns the result in r0 57 * Shuffle everything around appropriately. 58 * Note the 16 bytes that we pushed to save registers. 59 */ 60 mov r8, r0 /* copy signal_pending */ 61 mov r7, r1 /* syscall number */ 62 mov r0, r2 /* syscall args */ 63 mov r1, r3 64 ldm r12, { r2, r3, r4, r5, r6 } 65 66 /* This next sequence of code works in conjunction with the 67 * rewind_if_safe_syscall_function(). If a signal is taken 68 * and the interrupted PC is anywhere between 'safe_syscall_start' 69 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. 70 * The code sequence must therefore be able to cope with this, and 71 * the syscall instruction must be the final one in the sequence. 72 */ 73safe_syscall_start: 74 /* if signal_pending is non-zero, don't do the call */ 75 ldr r12, [r8] /* signal_pending */ 76 tst r12, r12 77 bne 1f 78 swi 0 79safe_syscall_end: 80 /* code path for having successfully executed the syscall */ 81 pop { r4, r5, r6, r7, r8, pc } 82 831: 84 /* code path when we didn't execute the syscall */ 85 ldr r0, =-TARGET_ERESTARTSYS 86 pop { r4, r5, r6, r7, r8, pc } 87 .fnend 88 .cfi_endproc 89 90 .size safe_syscall_base, .-safe_syscall_base 91