/* * 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 linux-user/safe-syscall.S * * Written by Richard Henderson <rth@twiddle.net> * Copyright (C) 2016 Red Hat, 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 /* 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'). * We return a long which is the syscall's return value, which * may be negative-errno on failure. Conversion to the * -1-and-errno-set convention is done by the calling wrapper. */ safe_syscall_base: .cfi_startproc stmg %r6,%r15,48(%r15) /* save all call-saved registers */ .cfi_offset %r15,-40 .cfi_offset %r14,-48 .cfi_offset %r13,-56 .cfi_offset %r12,-64 .cfi_offset %r11,-72 .cfi_offset %r10,-80 .cfi_offset %r9,-88 .cfi_offset %r8,-96 .cfi_offset %r7,-104 .cfi_offset %r6,-112 lgr %r1,%r15 lg %r0,8(%r15) /* load eos */ aghi %r15,-160 .cfi_adjust_cfa_offset 160 stg %r1,0(%r15) /* store back chain */ stg %r0,8(%r15) /* store eos */ /* The syscall calling convention isn't the same as the * C one: * we enter with r2 == *signal_pending * r3 == syscall number * r4, r5, r6, (stack) == syscall arguments * and return the result in r2 * and the syscall instruction needs * r1 == syscall number * r2 ... r7 == syscall arguments * and returns the result in r2 * Shuffle everything around appropriately. */ lgr %r8,%r2 /* signal_pending pointer */ lgr %r1,%r3 /* syscall number */ lgr %r2,%r4 /* syscall args */ lgr %r3,%r5 lgr %r4,%r6 lmg %r5,%r7,320(%r15) /* 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 */ icm %r0,15,0(%r8) jne 2f svc 0 safe_syscall_end: 1: lg %r15,0(%r15) /* load back chain */ .cfi_remember_state .cfi_adjust_cfa_offset -160 lmg %r6,%r15,48(%r15) /* load saved registers */ br %r14 .cfi_restore_state 2: lghi %r2, -TARGET_ERESTARTSYS j 1b .cfi_endproc .size safe_syscall_base, .-safe_syscall_base