fix: make getcwd report truncated buffers as ERANGE

kernel/src/Api/Process.hpp

@@ -165,10 +165,15 @@ namespace montauk::abi {
         if (proc == nullptr || buf == nullptr || maxLen == 0) return -1;
 
         const char* cwd = proc->cwd[0] ? proc->cwd : "0:/";
-        int i = 0;
-        for (; i < (int)maxLen - 1 && cwd[i]; i++) buf[i] = cwd[i];
-        buf[i] = '\0';
-        return i;
+        uint64_t cwdLen = 0;
+        while (cwd[cwdLen] != '\0') cwdLen++;
+
+        // Reserve -1 for non-size failures so libc can distinguish them
+        // from a buffer that can be retried with a larger allocation.
+        if (maxLen <= cwdLen) return -2;
+
+        for (uint64_t i = 0; i <= cwdLen; i++) buf[i] = cwd[i];
+        return (int)cwdLen;
     }
 
     // ====================================================================

programs/lib/libc/libc.c

@@ -2286,8 +2286,9 @@ char *getcwd(char *buf, size_t size) {
         errno = EINVAL;
         return NULL;
     }
-    if ((int)_zos_syscall2(SYS_GETCWD, (long)buf, (long)size) < 0) {
-        errno = ERANGE;
+    int result = (int)_zos_syscall2(SYS_GETCWD, (long)buf, (long)size);
+    if (result < 0) {
+        errno = result == -2 ? ERANGE : EIO;
         return NULL;
     }
     return buf;

programs/man/syscalls.2

@@ -64,7 +64,9 @@
         int montauk::chdir(const char* path);
 
 .B SYS_GETCWD (95)
-    Get the calling process's current working directory.
+    Get the calling process's current working directory. Returns the path
+    length on success, -2 if maxLen cannot hold the path and terminating NUL,
+    or -1 for another failure. The buffer is not modified when it is too small.
         int montauk::getcwd(char* buf, uint64_t maxLen);
 
 .B SYS_SETUSER (92)