Add basic parsing for underlying ELF executables

The given initrd is a CPIO archive of multiple ELF executables. We are
already able to parse the CPIO archive to detect where each file is
located, this commit adds the mapping for each ELF executable to the
corresponding task_struct.

Note that this is still heavily under construction, since we cannot
simply jump into the entry point of an executable as we have not yet
setup the proper layout from performing context switches.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 36 insertions, 4 deletions

diff --git a/kernel/initrd.c b/kernel/initrd.c
index c05e77d..4706fe8 100644
--- a/kernel/initrd.c
+++ b/kernel/initrd.c
@@ -63,16 +63,48 @@ __kernel int get_task_id_from_name(const char *const name)
 	return TASK_UNKNOWN;
 }
 
-__kernel void extract_elf(int task_id, const char *const addr, size_t size)
+__kernel void ensure_elf_format(const unsigned char *const addr)
+{
+	if (addr[0] != 0x7F || memcmp(&addr[1], "ELF", 3) != 0) {
+		die("Bad ELF format\n");
+	}
+	if (addr[4] != 2) {
+		die("64-bit format is mandatory\n");
+	}
+	if (addr[5] != 1) {
+		die("Little-endian only\n");
+	}
+}
+
+struct exec_header {
+	uint64_t e_entry;
+	uint64_t e_phoff;
+	uint16_t e_phnum;
+	uint16_t e_phentsize;
+};
+
+// TODO
+__kernel void extract_elf(int task_id, const unsigned char *const addr, size_t size)
 {
 	__unused(task_id);
-	__unused(addr);
 	__unused(size);
 
-	// TODO
+	ensure_elf_format(addr);
+
+	/* struct exec_header header = { */
+	/* 	.e_entry = (unsigned long long)addr[0x18], */
+	/* 	.e_phoff = (uint64_t)addr[0x20], */
+	/* 	.e_phentsize = (uint16_t)addr[0x36], */
+	/* 	.e_phnum = (uint16_t)addr[0x38], */
+	/* }; */
+
+#ifdef __KERNEL__
+	tasks[task_id].addr = (const void *)addr;
+	tasks[task_id].entry_offset = (uint64_t)addr[0x18];
+#endif
 }
 
-__kernel void extract_initrd(const char *const initrd_addr, uint64_t size)
+__kernel void extract_initrd(const unsigned char *const initrd_addr, uint64_t size)
 {
 	char buffer[BUFFER_SIZE];
 	uint64_t name_size, file_size, padding, base = 0;