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