Function handle_syscall

kernel/src/syscalls.rs:177–273

()

///
#[naked]
extern "C" fn handle_syscall() {
    unsafe {
        asm!(
            // Here we switch stack to avoid messing with user stack
            // swapgs is a way to do this
            // - <https://github.com/redox-os/kernel/blob/master/src/arch/x86_64/interrupt/syscall.rs#L65>
            // - <https://www.felixcloutier.com/x86/swapgs>

            "swapgs", // Put the TSS address into GS (stored in syscalls::init)
            "mov gs:{tss_temp}, rsp", // Save user stack pointer in TSS entry

            "mov rsp, gs:{tss_timer}", // Get kernel stack pointer
            "sub rsp, {ks_offset}", // Use a different location than timer interrupt

            // Create an Exception stack frame
            "sub rsp, 8", // To be replaced with SS
            "push gs:{tss_temp}", // User stack pointer
            "swapgs", // Put TSS address back

            // Could re-enable interrupts here?

            "push r11", // Caller's RFLAGS
            "sub rsp, 8",  // CS
            "push rcx", // Caller's RIP

            // Create the remainder of the Context struct
            "push rax",
            "push rbx",
            "push rcx",
            "push rdx",

            "push rdi",
            "push rsi",
            "push rbp",
            "push r8",

            "push r9",
            "push r10",
            "push r11",
            "push r12",

            "push r13",
            "push r14",
            "push r15",

            // Call the rust dispatch_syscall function
            // C calling convention so arguments are in registers
            // RDI, RSI, RDX, RCX, R8, R9
            "mov r8, rdx", // Fifth argument <- Syscall third argument
            "mov rcx, rsi", // Fourth argument <- Syscall second argument
            "mov rdx, rdi", // Third argument <- Syscall first argument
            "mov rsi, rax", // Second argument is the syscall number
            "mov rdi, rsp", // First argument is the Context address
            "call {dispatch_fn}",

            "pop r15", // restore callee-saved registers
            "pop r14",
            "pop r13",