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sortix--sortix/kernel/x64/syscall.S
2015-08-26 16:29:18 +02:00

98 lines
2.8 KiB
ArmAsm

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014, 2015.
This file is part of Sortix.
Sortix is free software: you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any later
version.
Sortix is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.
You should have received a copy of the GNU General Public License along with
Sortix. If not, see <http://www.gnu.org/licenses/>.
x64/syscall.S
An assembly stub that acts as glue for system calls.
*******************************************************************************/
#include <sortix/syscall.h>
.global syscall_handler
.section .text
.type syscall_handler, @function
syscall_handler:
movl $0, global_errno # Reset errno
pushq %rbp
movq %rsp, %rbp
# Make sure the requested system call is valid, if not, then fix it.
cmp $SYSCALL_MAX_NUM, %rax
jae 3f
1:
# Read a system call function pointer.
xorq %r11, %r11
movq syscall_list(%r11,%rax,8), %rax
# Oh how nice, user-space put the parameters in: rdi, rsi, rdx, rcx, r8, r9
# Call the system call.
callq *%rax
# Return to user-space, system call result in %rax:%rdx, errno in %ecx.
popq %rbp
movl global_errno, %ecx
# Zero registers to avoid information leaks.
# rax is return value.
# rdi is set in a moment.
xor %rsi, %rsi
# rdx is return value (MIGHT NOT BE INITIALIZED, CAN LEAK!).
# rcx is errno.
xor %r8, %r8
xor %r9, %r9
xor %r10, %r10
xor %r11, %r11
# The rest of the registers are preserved by the ABI and syscall ABI.
# If any signals are pending, fire them now.
movq asm_signal_is_pending, %rdi
testq %rdi, %rdi
jnz 4f
# rdi is zero in this branch.
2:
iretq
3:
# Call the null system call instead.
xorq %rax, %rax
jmp 1b
4:
# We can't return to this location after the signal, since if any system
# call is made this stack will get reused and all our nice temporaries wil
# be garbage. We therefore pass the kernel the state to return to and it'll
# handle it for us when the signal is over.
movq 0(%rsp), %rdi # userspace rip
movq 16(%rsp), %rsi # userspace rflags
movq 24(%rsp), %r8 # userspace rsp, note %rcx is used for errno
int $130 # Deliver pending signals.
# If we end up here, it means that the signal didn't override anything and
# that we should just go ahead and return to userspace ourselves. Zero the
# scratch registers to avoid information leaks.
xor %rdi, %rdi
xor %rsi, %rsi
xor %r8, %r8
jmp 2b
.size syscall_handler, .-syscall_handler