create a bootstrap ELF loader, that'll load init

6 files changed, 94 insertions, 0 deletions

diff --git a/src/user_bootstrap/elfload.c b/src/user_bootstrap/elfload.c
new file mode 120000
index 0000000..75a5cb2
--- /dev/null
+++ b/src/user_bootstrap/elfload.c
@@ -0,0 +1 @@
+../user/lib/elfload.c
\ No newline at end of file
diff --git a/src/user_bootstrap/elfload.h b/src/user_bootstrap/elfload.h
new file mode 120000
index 0000000..5b09fdc
--- /dev/null
+++ b/src/user_bootstrap/elfload.h
@@ -0,0 +1 @@
+../user/lib/elfload.h
\ No newline at end of file
diff --git a/src/user_bootstrap/linker.ld b/src/user_bootstrap/linker.ld
new file mode 100644
index 0000000..f2c9d24
--- /dev/null
+++ b/src/user_bootstrap/linker.ld
@@ -0,0 +1,31 @@
+ENTRY(main)
+OUTPUT_FORMAT("binary")
+
+SECTIONS
+{
+	. = 2M;
+	.text BLOCK(4K) : ALIGN(4K)
+	{
+		*(.text.startup)
+		*(.text)
+	}
+	.rodata BLOCK(4K) : ALIGN(4K)
+	{
+		*(.rodata)
+	}
+	.data BLOCK(4K) : ALIGN(4K)
+	{
+		*(.data)
+	}
+
+	_initrd = .; /* is just appended onto the end of the binary */
+	. += 2M;
+
+	_bss_start = .;
+	.bss BLOCK(4K) : ALIGN(4K)
+	{
+		*(COMMON)
+		*(.bss)
+	}
+	_bss_end = .;
+}
diff --git a/src/user_bootstrap/main.c b/src/user_bootstrap/main.c
new file mode 100644
index 0000000..baa9803
--- /dev/null
+++ b/src/user_bootstrap/main.c
@@ -0,0 +1,59 @@
+#include <shared/flags.h>
+#include <shared/mem.h>
+#include <shared/syscalls.h>
+#include <user_bootstrap/elfload.h>
+
+extern char _bss_start;
+extern char _bss_end;
+extern char _initrd;
+
+/* libc stubs */
+int printf(const char *fmt, ...) {(void)fmt; return 0;}
+void *malloc(size_t size) {(void)size; _syscall_exit(1);}
+void free(void *ptr) {}
+int file_read(libc_file *f, char *buf, size_t len) {(void)f; (void)buf; (void)len; _syscall_exit(1);}
+
+
+static void *tar_find(void *tar, const char *path);
+static int oct_parse(char *str, size_t len);
+
+static void *tar_find(void *tar, const char *path) {
+	size_t path_len = strlen(path);
+	int size;
+	if (path_len > 100) return NULL;
+
+	for (size_t off = 0;;) {
+		if (0 != memcmp(tar + off + 257, "ustar", 5))
+			return NULL; // not a metadata sector, end of archive
+
+		size = oct_parse(tar + off + 124, 11);
+		if (0 == memcmp(tar + off, path, path_len) &&
+				*(char*)(tar + off + path_len) == '\0')
+		{
+			return tar + off + 512;
+		}
+		off += 512;
+		off += (size + 511) & ~511;
+	}
+}
+
+static int oct_parse(char *str, size_t len) {
+	int res = 0;
+	for (size_t i = 0; i < len; i++) {
+		res *= 8;
+		res += str[i] - '0'; // no format checking
+	}
+	return res;
+}
+
+
+__attribute__((section(".text.startup")))
+int main(void) {
+	_syscall_memflag(&_bss_start, &_bss_end - &_bss_start, MEMFLAG_PRESENT);
+
+	void *init = tar_find(&_initrd, "test.elf");
+	elf_exec(init);
+	_syscall_debug_klog("bootstrap failed", sizeof("bootstrap failed"));
+
+	_syscall_exit(0);
+}
diff --git a/src/user_bootstrap/syscall.c b/src/user_bootstrap/syscall.c
new file mode 120000
index 0000000..c6d5b0f
--- /dev/null
+++ b/src/user_bootstrap/syscall.c
@@ -0,0 +1 @@
+../user/lib/syscall.c
\ No newline at end of file
diff --git a/src/user_bootstrap/syscall.s b/src/user_bootstrap/syscall.s
new file mode 120000
index 0000000..ac2e0f9
--- /dev/null
+++ b/src/user_bootstrap/syscall.s
@@ -0,0 +1 @@
+../user/lib/syscall.s
\ No newline at end of file