refactor: move the native devkit from 0:/usr to 0:/sdk (Montauk SDK)

0:/usr was a Unix transplant in an otherwise Montauk-native layout.
The SDK now lives at 0:/sdk/{bin,include,lib} (+ ldscripts under
0:/sdk/x86_64-montauk): Montauk-flavored, and a clean unit for a
future per-component installer tickbox. Native binutils is rebuilt
with --prefix=/sdk so ld's compiled-in search paths follow; future
ports configure with --prefix=/sdk.

Also add pathconf() with _PC_* names to the libc: now that realpath
exists, libiberty's lrealpath.c compiles its pathconf fallback path
unconditionally.

Shell command resolution and tab completion updated to 0:/sdk/bin.
Boot-verified in QEMU: setup, login, desktop on the new image with
zero usr/ remnants in the ramdisk.

Co-Authored-By: Claude Fable 5 <[email protected]>

programs/GNUmakefile

@@ -377,30 +377,31 @@ $(BINDIR)/os/%.elf: src/%/main.cpp link.ld GNUmakefile
 	$(CXX) $(CXXFLAGS) $(LDFLAGS) obj/$*/main.o lib/libc/liblibc.a -o $@
 
 # ============================================================================
-# Native development kit: binutils built for MontaukOS plus a target
-# sysroot (headers, libc.a, crt objects) under 0:/usr. Skipped when the
-# native tools have not been built; see toolchain/README.md.
+# Native development kit (Montauk SDK): binutils built for MontaukOS
+# plus a target sysroot (headers, libc.a, crt objects) under 0:/sdk.
+# Skipped when the native tools have not been built; see
+# toolchain/README.md.
 # ============================================================================
-NATIVE_BIN := ../toolchain/native/usr/bin
+NATIVE_BIN := ../toolchain/native/sdk/bin
 DEVKIT_TOOLS := as ld ar nm objcopy objdump readelf ranlib strip size strings addr2line c++filt elfedit
 
 .PHONY: devkit
 devkit: libc
 ifneq ($(wildcard $(NATIVE_BIN)/as),)
-	rm -rf $(BINDIR)/usr
-	mkdir -p $(BINDIR)/usr/bin $(BINDIR)/usr/lib $(BINDIR)/usr/include
+	rm -rf $(BINDIR)/sdk
+	mkdir -p $(BINDIR)/sdk/bin $(BINDIR)/sdk/lib $(BINDIR)/sdk/include
 	for t in $(DEVKIT_TOOLS); do \
-	    cp $(NATIVE_BIN)/$$t $(BINDIR)/usr/bin/$$t.elf || exit 1; \
+	    cp $(NATIVE_BIN)/$$t $(BINDIR)/sdk/bin/$$t.elf || exit 1; \
 	done
-	cp -r ../toolchain/native/usr/x86_64-montauk $(BINDIR)/usr/x86_64-montauk
-	cp -r include/libc/. $(BINDIR)/usr/include/
-	cp -r include/montauk $(BINDIR)/usr/include/montauk
-	cp -r include/Api $(BINDIR)/usr/include/Api
-	cp -r ../kernel/freestnd-cxx-hdrs/x86_64/include/. $(BINDIR)/usr/include/
-	cp lib/libc/liblibc.a $(BINDIR)/usr/lib/libc.a
-	cp lib/libc/crt1.o lib/libc/crti.o lib/libc/crtn.o $(BINDIR)/usr/lib/
-	ar rcs $(BINDIR)/usr/lib/libm.a
-	ar rcs $(BINDIR)/usr/lib/libstdc++.a
+	cp -r ../toolchain/native/sdk/x86_64-montauk $(BINDIR)/sdk/x86_64-montauk
+	cp -r include/libc/. $(BINDIR)/sdk/include/
+	cp -r include/montauk $(BINDIR)/sdk/include/montauk
+	cp -r include/Api $(BINDIR)/sdk/include/Api
+	cp -r ../kernel/freestnd-cxx-hdrs/x86_64/include/. $(BINDIR)/sdk/include/
+	cp lib/libc/liblibc.a $(BINDIR)/sdk/lib/libc.a
+	cp lib/libc/crt1.o lib/libc/crti.o lib/libc/crtn.o $(BINDIR)/sdk/lib/
+	ar rcs $(BINDIR)/sdk/lib/libm.a
+	ar rcs $(BINDIR)/sdk/lib/libstdc++.a
 else
 	@echo "devkit: toolchain/native/ not built; skipping native dev tools"
 endif

programs/include/libc/unistd.h

@@ -38,6 +38,15 @@ int    execv(const char *path, char *const argv[]);
 int    execve(const char *path, char *const argv[], char *const envp[]);
 int    execvp(const char *file, char *const argv[]);
 int    pipe(int fds[2]);
+long   pathconf(const char *path, int name);
+
+/* pathconf() names (Linux numbering). */
+#define _PC_LINK_MAX  0
+#define _PC_MAX_CANON 1
+#define _PC_MAX_INPUT 2
+#define _PC_NAME_MAX  3
+#define _PC_PATH_MAX  4
+#define _PC_PIPE_BUF  5
 
 extern char **environ;
 

programs/lib/libc/libc.c

@@ -3435,6 +3435,19 @@ int kill(pid_t pid, int sig) {
     return 0;
 }
 
+long pathconf(const char *path, int name) {
+    (void)path;
+    switch (name) {
+    case 3:   /* _PC_NAME_MAX */
+        return 255;
+    case 4:   /* _PC_PATH_MAX */
+        return 4096;
+    default:
+        errno = EINVAL;
+        return -1;
+    }
+}
+
 /* The libc environment lives in name/value slots (getenv/setenv), not
    NAME=VALUE strings, and exec* is unimplemented, so nothing can
    consume a populated environ yet. An empty, valid vector satisfies

programs/src/shell/exec.cpp

@@ -84,8 +84,8 @@ int exec_external(const char* cmd, const char* args) {
     scat(path, name, sizeof(path));
     if (try_exec(path, finalArgs)) return 0;
 
-    // 5. Try 0:/usr/bin/<cmd>.elf (native dev tools: as, ld, ar, ...)
-    scopy(path, "0:/usr/bin/", sizeof(path));
+    // 5. Try 0:/sdk/bin/<cmd>.elf (Montauk SDK: as, ld, ar, ...)
+    scopy(path, "0:/sdk/bin/", sizeof(path));
     scat(path, name, sizeof(path));
     scat(path, ".elf", sizeof(path));
     if (try_exec(path, finalArgs)) return 0;

programs/src/shell/tabcompletion.cpp

@@ -148,14 +148,14 @@ int get_completions(		// returns no. of results
 		} 
 	}
 
-	// ---- Native dev tools (0:/usr/bin/*.elf) ----
+	// ---- Montauk SDK tools (0:/sdk/bin/*.elf) ----
 
 	const char* usr_names[RD_MAX]	= { };
 
-	int un = montauk::readdir("0:/usr/bin", usr_names, RD_MAX);
+	int un = montauk::readdir("0:/sdk/bin", usr_names, RD_MAX);
 
 	for (int i = 0; i < un; i++) {
-		/* Entries come back as "usr/bin/as.elf"; strip to the last
+		/* Entries come back as "sdk/bin/as.elf"; strip to the last
 		   slash, not the first. */
 		int inc = 0;
 		for (int j = 0; usr_names[i][j]; j++) {