tool headers nolibc: add RISCV support

This adds support for the RISCV architecture (32 and 64 bit) to the
nolibc header file.
Signed-off-by: NPranith Kumar <bobby.prani@gmail.com>
[willy: minimal rewording of the commit message]
Signed-off-by: NWilly Tarreau <w@1wt.eu>

tools/include/nolibc/nolibc.h

@@ -1243,6 +1243,200 @@ struct sys_stat_struct {
 	long          st_pad4[14];
 };
 
+#elif defined(__riscv)
+
+#if   __riscv_xlen == 64
+#define PTRLOG "3"
+#define SZREG  "8"
+#elif __riscv_xlen == 32
+#define PTRLOG "2"
+#define SZREG  "4"
+#endif
+
+/* Syscalls for RISCV :
+ *   - stack is 16-byte aligned
+ *   - syscall number is passed in a7
+ *   - arguments are in a0, a1, a2, a3, a4, a5
+ *   - the system call is performed by calling ecall
+ *   - syscall return comes in a0
+ *   - 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.
+ */
+
+#define my_syscall0(num)                                                      \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0");                                        \
+									      \
+	asm volatile (                                                        \
+		"ecall\n\t"                                                   \
+		: "=r"(_arg1)                                                 \
+		: "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall1(num, arg1)                                                \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);		              \
+									      \
+	asm volatile (                                                        \
+		"ecall\n"                                                     \
+		: "+r"(_arg1)                                                 \
+		: "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);                         \
+	register long _arg2 asm("a1") = (long)(arg2);                         \
+									      \
+	asm volatile (                                                        \
+		"ecall\n"                                                     \
+		: "+r"(_arg1)                                                 \
+		: "r"(_arg2),                                                 \
+		  "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall3(num, arg1, arg2, arg3)                                    \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);                         \
+	register long _arg2 asm("a1") = (long)(arg2);                         \
+	register long _arg3 asm("a2") = (long)(arg3);                         \
+									      \
+	asm volatile (                                                        \
+		"ecall\n\t"                                                   \
+		: "+r"(_arg1)                                                 \
+		: "r"(_arg2), "r"(_arg3),                                     \
+		  "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);                         \
+	register long _arg2 asm("a1") = (long)(arg2);                         \
+	register long _arg3 asm("a2") = (long)(arg3);                         \
+	register long _arg4 asm("a3") = (long)(arg4);                         \
+									      \
+	asm volatile (                                                        \
+		"ecall\n"                                                     \
+		: "+r"(_arg1)                                                 \
+		: "r"(_arg2), "r"(_arg3), "r"(_arg4),                         \
+		  "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);                         \
+	register long _arg2 asm("a1") = (long)(arg2);                         \
+	register long _arg3 asm("a2") = (long)(arg3);                         \
+	register long _arg4 asm("a3") = (long)(arg4);                         \
+	register long _arg5 asm("a4") = (long)(arg5);                         \
+									      \
+	asm volatile (                                                        \
+		"ecall\n"                                                     \
+		: "+r"(_arg1)                                                 \
+		: "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5),             \
+		  "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
+({                                                                            \
+	register long _num  asm("a7") = (num);                                \
+	register long _arg1 asm("a0") = (long)(arg1);                         \
+	register long _arg2 asm("a1") = (long)(arg2);                         \
+	register long _arg3 asm("a2") = (long)(arg3);                         \
+	register long _arg4 asm("a3") = (long)(arg4);                         \
+	register long _arg5 asm("a4") = (long)(arg5);                         \
+	register long _arg6 asm("a5") = (long)(arg6);                         \
+									      \
+	asm volatile (                                                        \
+		"ecall\n"                                                     \
+		: "+r"(_arg1)                                                 \
+		: "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), "r"(_arg6), \
+		  "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_arg1;                                                                \
+})
+
+/* startup code */
+asm(".section .text\n"
+    ".global _start\n"
+    "_start:\n"
+    ".option push\n"
+    ".option norelax\n"
+    "lla   gp, __global_pointer$\n"
+    ".option pop\n"
+    "ld    a0, 0(sp)\n"          // argc (a0) was in the stack
+    "add   a1, sp, "SZREG"\n"    // argv (a1) = sp
+    "slli  a2, a0, "PTRLOG"\n"   // envp (a2) = SZREG*argc ...
+    "add   a2, a2, "SZREG"\n"    //             + SZREG (skip null)
+    "add   a2,a2,a1\n"           //             + argv
+    "andi  sp,a1,-16\n"          // sp must be 16-byte aligned
+    "call  main\n"               // main() returns the status code, we'll exit with it.
+    "andi  a0, a0, 0xff\n"       // limit exit code to 8 bits
+    "li a7, 93\n"                // NR_exit == 93
+    "ecall\n"
+    "");
+
+/* fcntl / open */
+#define O_RDONLY            0
+#define O_WRONLY            1
+#define O_RDWR              2
+#define O_CREAT         0x100
+#define O_EXCL          0x200
+#define O_NOCTTY        0x400
+#define O_TRUNC        0x1000
+#define O_APPEND       0x2000
+#define O_NONBLOCK     0x4000
+#define O_DIRECTORY  0x200000
+
+struct sys_stat_struct {
+	unsigned long	st_dev;		/* Device.  */
+	unsigned long	st_ino;		/* File serial number.  */
+	unsigned int	st_mode;	/* File mode.  */
+	unsigned int	st_nlink;	/* Link count.  */
+	unsigned int	st_uid;		/* User ID of the file's owner.  */
+	unsigned int	st_gid;		/* Group ID of the file's group. */
+	unsigned long	st_rdev;	/* Device number, if device.  */
+	unsigned long	__pad1;
+	long		st_size;	/* Size of file, in bytes.  */
+	int		st_blksize;	/* Optimal block size for I/O.  */
+	int		__pad2;
+	long		st_blocks;	/* Number 512-byte blocks allocated. */
+	long		st_atime;	/* Time of last access.  */
+	unsigned long	st_atime_nsec;
+	long		st_mtime;	/* Time of last modification.  */
+	unsigned long	st_mtime_nsec;
+	long		st_ctime;	/* Time of last status change.  */
+	unsigned long	st_ctime_nsec;
+	unsigned int	__unused4;
+	unsigned int	__unused5;
+};
+
 #endif