tools/include/nolibc/arch-x86_64.h


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/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
/*
 * x86_64 specific definitions for NOLIBC
 * Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu>
 */

#ifndef _NOLIBC_ARCH_X86_64_H
#define _NOLIBC_ARCH_X86_64_H

#include "compiler.h"
#include "crt.h"

/* Syscalls for x86_64 :
 *   - registers are 64-bit
 *   - syscall number is passed in rax
 *   - arguments are in rdi, rsi, rdx, r10, r8, r9 respectively
 *   - the system call is performed by calling the syscall instruction
 *   - syscall return comes in rax
 *   - rcx and r11 are clobbered, others are preserved.
 *   - the arguments are cast to long and assigned into the target registers
 *     which are then simply passed as registers to the asm code, so that we
 *     don't have to experience issues with register constraints.
 *   - the syscall number is always specified last in order to allow to force
 *     some registers before (gcc refuses a %-register at the last position).
 *   - see also x86-64 ABI section A.2 AMD64 Linux Kernel Conventions, A.2.1
 *     Calling Conventions.
 *
 * Link x86-64 ABI: https://gitlab.com/x86-psABIs/x86-64-ABI/-/wikis/home
 *
 */

#define my_syscall0(num)                                                      \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall1(num, arg1)                                                \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1),                                                 \
		  "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall2(num, arg1, arg2)                                          \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1), "r"(_arg2),                                     \
		  "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall3(num, arg1, arg2, arg3)                                    \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1), "r"(_arg2), "r"(_arg3),                         \
		  "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),             \
		  "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
	register long _arg5 __asm__ ("r8")  = (long)(arg5);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
		  "0"(_num)                                                   \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
({                                                                            \
	long _ret;                                                            \
	register long _num  __asm__ ("rax") = (num);                          \
	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
	register long _arg5 __asm__ ("r8")  = (long)(arg5);                   \
	register long _arg6 __asm__ ("r9")  = (long)(arg6);                   \
									      \
	__asm__ volatile (                                                    \
		"syscall\n"                                                   \
		: "=a"(_ret)                                                  \
		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
		  "r"(_arg6), "0"(_num)                                       \
		: "rcx", "r11", "memory", "cc"                                \
	);                                                                    \
	_ret;                                                                 \
})

/* startup code */
/*
 * x86-64 System V ABI mandates:
 * 1) %rsp must be 16-byte aligned right before the function call.
 * 2) The deepest stack frame should be zero (the %rbp).
 *
 */
void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
{
	__asm__ volatile (
		"xor  %ebp, %ebp\n"       /* zero the stack frame                            */
		"mov  %rsp, %rdi\n"       /* save stack pointer to %rdi, as arg1 of _start_c */
		"and  $-16, %rsp\n"       /* %rsp must be 16-byte aligned before call        */
		"call _start_c\n"         /* transfer to c runtime                           */
		"hlt\n"                   /* ensure it does not return                       */
	);
	__builtin_unreachable();
}

#endif /* _NOLIBC_ARCH_X86_64_H */