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Use C strings for system calls.

    We used Myrddin strings, which are not nul terminated, when
    entering the system. Since Posix systems use nul terminated
    strings for paths and such in system calls, this was wrong.

    Now, strings are allocated on the stack by an assembly function
    that does some trickery with stack pointer adjustment, and passed
    to the kernel that way. This should not be a bottleneck, and
    allows us to keep slicing strings.

--- a/libstd/Makefile

+++ b/libstd/Makefile

@@ -12,7 +12,8 @@

 ASMSRC= \

     start.s \

-    syscall.s

+    syscall.s \

+    util.s

 include ../config.mk

--- a/libstd/sys-linux.myr

+++ b/libstd/sys-linux.myr

@@ -369,6 +369,7 @@

 	const Sysprocess_vm_writev	: scno = 311

 	extern const syscall : (sc:scno, args:... -> int64)

+	extern const cstring : (str : byte[:] -> byte*)

 	const exit	: (status:int64 -> void)

 	const getpid	: ( -> int64)

@@ -387,9 +388,9 @@

 const exit	= {status;		syscall(Sysexit, 1);}

 const getpid	= {;			-> syscall(Sysgetpid, 1);}

 const kill	= {pid, sig;		-> syscall(Syskill, pid, sig);}

-const open	= {path, opts, mode;	-> syscall(Sysopen, path castto(char*), opts);}

+const open	= {path, opts, mode;	-> syscall(Sysopen, cstring(path), opts, mode);}

 const close	= {fd;			-> syscall(Sysclose, fd);}

-const creat	= {path, mode;		-> syscall(Syscreat, path castto(char*), mode);}

+const creat	= {path, mode;		-> syscall(Syscreat, cstring(path), mode);}

 const read	= {fd, buf;		-> syscall(Sysread, fd, buf castto(char*), buf.len);}

 const write	= {fd, buf;		-> syscall(Syswrite, fd, buf castto(char*), buf.len castto(size));}

 const lseek	= {fd, off, whence;	-> syscall(Syslseek, fd, off, whence);}

--- a/libstd/sys-osx.myr

+++ b/libstd/sys-osx.myr

@@ -433,7 +433,7 @@

 const exit	= {status;		syscall(Sysexit, 1);}

 const getpid	= {;			-> syscall(Sysgetpid, 1);}

 const kill	= {pid, sig;		-> syscall(Syskill, pid, sig);}

-const open	= {path, opts, mode;	-> syscall(Sysopen, path castto(char*), opts);}

+const open	= {path, opts, mode;	-> syscall(Sysopen, cstring(path) opts, mode);}

 const close	= {fd;			-> syscall(Sysclose, fd);}

 const creat	= {path, mode;		-> open(path, Ocreat | Otrunc | Owronly, mode);}

 const read	= {fd, buf;		-> syscall(Sysread, fd, buf castto(char*), buf.len);}

--- a/libstd/syscall-linux.s

+++ b/libstd/syscall-linux.s

@@ -20,3 +20,4 @@

 	popq %rbp

 	ret

+

--- a/myrbuild/myrbuild.c

+++ b/myrbuild/myrbuild.c

@@ -162,7 +162,7 @@

     char *localdep;

     char *deps[512];

     char buf[1024];

-    char *extra[2] = {"-o", "" /* filename */};

+    char *extra[] = {"-g", "-o", "" /* filename */};

     if (hassuffix(file, ".myr")) {

         getdeps(file, deps, 512, &ndeps);

@@ -189,8 +189,8 @@

     } else if (hassuffix(file, ".s")) {

         swapsuffix(buf, sizeof buf, file, ".s", ".o");

         if (isfresh(file, buf)) {

-            extra[1] = buf;

-            gencmd(&cmd, &ncmd, as, file, extra, 2);

+            extra[2] = buf;

+            gencmd(&cmd, &ncmd, as, file, extra, 3);

             run(cmd);

         }

     }