tools/nolibc: add missing my_syscall6() for mips

It is able to pass the 6th argument like the 5th argument via the stack
for mips, let's add a new my_syscall6() now, see [1] for details:

  The mips/o32 system call convention passes arguments 5 through 8 on
  the user stack.

Both mmap() and pselect6() require my_syscall6().

[1]: https://man7.org/linux/man-pages/man2/syscall.2.htmlSigned-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

tools/include/nolibc/arch-mips.h

@@ -166,7 +166,7 @@ struct sys_stat_struct {
 	__asm__ volatile (                                                    \
 		"addiu $sp, $sp, -32\n"                                       \
 		"sw %7, 16($sp)\n"                                            \
-		"syscall\n  "                                                 \
+		"syscall\n"                                                   \
 		"addiu $sp, $sp, 32\n"                                        \
 		: "=r" (_num), "=r"(_arg4)                                    \
 		: "0"(_num),                                                  \
@@ -176,6 +176,31 @@ struct sys_stat_struct {
 	_arg4 ? -_num : _num;                                                 \
 })
 
+#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
+({                                                                            \
+	register long _num __asm__ ("v0")  = (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 = (long)(arg5);                                   \
+	register long _arg6 = (long)(arg6);                                   \
+									      \
+	__asm__ volatile (                                                    \
+		"addiu $sp, $sp, -32\n"                                       \
+		"sw %7, 16($sp)\n"                                            \
+		"sw %8, 20($sp)\n"                                            \
+		"syscall\n"                                                   \
+		"addiu $sp, $sp, 32\n"                                        \
+		: "=r" (_num), "=r"(_arg4)                                    \
+		: "0"(_num),                                                  \
+		  "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
+		  "r"(_arg6)                                                  \
+		: _NOLIBC_SYSCALL_CLOBBERLIST                                 \
+	);                                                                    \
+	_arg4 ? -_num : _num;                                                 \
+})
+
 char **environ __attribute__((weak));
 const unsigned long *_auxv __attribute__((weak));
 

tools/include/nolibc/nolibc.h

@@ -13,11 +13,10 @@
  * Syscalls are split into 3 levels:
  *   - The lower level is the arch-specific syscall() definition, consisting in
  *     assembly code in compound expressions. These are called my_syscall0() to
- *     my_syscall6() depending on the number of arguments. The MIPS
- *     implementation is limited to 5 arguments. All input arguments are cast
- *     to a long stored in a register. These expressions always return the
- *     syscall's return value as a signed long value which is often either a
- *     pointer or the negated errno value.
+ *     my_syscall6() depending on the number of arguments. All input arguments
+ *     are castto a long stored in a register. These expressions always return
+ *     the syscall's return value as a signed long value which is often either
+ *     a pointer or the negated errno value.
  *
  *   - The second level is mostly architecture-independent. It is made of
  *     static functions called sys_<name>() which rely on my_syscallN()