// Copyright 2016 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#include <asm.h>
#include <arch/regs.h>
#include <arch/x86/descriptor.h>
#include <zircon/compiler.h>
#include <zircon/tls.h>

// x86_uspace_entry(iframe_t* iframe)
// optionally vaddr_t unsafe_sp top
FUNCTION(x86_uspace_entry)
#if __has_feature(safe_stack)
    mov  %rsi, %gs:ZX_TLS_UNSAFE_SP_OFFSET
#endif

    /* push a fake 64bit interrupt stack frame and iret to it */
    push_value X86_IFRAME_OFFSET_USER_SS(%rdi) // ss
    push_value X86_IFRAME_OFFSET_USER_SP(%rdi) // sp
    push_value X86_IFRAME_OFFSET_FLAGS(%rdi)   // rflags
    push_value X86_IFRAME_OFFSET_CS(%rdi)      // cs
    push_value X86_IFRAME_OFFSET_IP(%rdi)      // pc

    ALL_CFI_UNDEFINED

    // Copy the remaining register state from |iframe|.
    movq X86_IFRAME_OFFSET_RAX(%rdi), %rax
    movq X86_IFRAME_OFFSET_RBX(%rdi), %rbx
    movq X86_IFRAME_OFFSET_RCX(%rdi), %rcx
    movq X86_IFRAME_OFFSET_RDX(%rdi), %rdx
    movq X86_IFRAME_OFFSET_RBP(%rdi), %rbp
    movq X86_IFRAME_OFFSET_RSI(%rdi), %rsi
    // Setting rdi deferred to last, we're still using it.
    movq X86_IFRAME_OFFSET_R8(%rdi), %r8
    movq X86_IFRAME_OFFSET_R9(%rdi), %r9
    movq X86_IFRAME_OFFSET_R10(%rdi), %r10
    movq X86_IFRAME_OFFSET_R11(%rdi), %r11
    movq X86_IFRAME_OFFSET_R12(%rdi), %r12
    movq X86_IFRAME_OFFSET_R13(%rdi), %r13
    movq X86_IFRAME_OFFSET_R14(%rdi), %r14
    movq X86_IFRAME_OFFSET_R15(%rdi), %r15
    movq X86_IFRAME_OFFSET_RDI(%rdi), %rdi

    // We do not need to clear extended register state, since the kernel only
    // uses the general purpose registers, and the extended state is
    // initialized to a cleared state.  Likewise the segment registers are
    // always cleared on context-switch, so their starting state is fine.  The
    // fs.base and gs.base values or the extended register state might have
    // been set via thread_write_state while the thread was suspended before
    // entering userspace and those values should be preserved.

    swapgs
    iretq
END_FUNCTION(x86_uspace_entry)