user: a super primitive ELF loader

holy shit.
this was simpler than i expected it to be

1 files changed, 59 insertions, 0 deletions

diff --git a/src/user/lib/elfload.c b/src/user/lib/elfload.c
new file mode 100644
index 0000000..67cef68
--- /dev/null
+++ b/src/user/lib/elfload.c
@@ -0,0 +1,59 @@
+#include <shared/flags.h>
+#include <shared/syscalls.h>
+#include <user/lib/elf.h>
+#include <user/lib/elfload.h>
+
+void elf_execf(libc_file *f) {
+	const size_t cap = 0x60000;
+	size_t pos = 0;
+	void *buf = malloc(cap); // TODO a way to get file size
+	if (!buf) goto fail;
+
+	while (!f->eof) {
+		long ret = file_read(f, buf, cap - pos);
+		if (ret < 0) goto fail;
+		pos += ret;
+		if (pos >= cap) goto fail;
+	}
+	elf_exec(buf);
+
+fail:
+	free(buf);
+}
+
+static bool valid_ehdr(const struct Elf64_Ehdr *h) {
+	return h->e_ident[0] == 0x7f
+		&& h->e_ident[1] == 'E'
+		&& h->e_ident[2] == 'L'
+		&& h->e_ident[3] == 'F'
+		&& h->e_type == ET_EXEC
+		&& h->e_machine == EM_X86_64
+		&& h->e_version == 1;
+}
+
+static bool load_phdr(const void *base, size_t idx) {
+	const struct Elf64_Ehdr *ehdr = base;
+	const struct Elf64_Phdr *phdr = base + ehdr->e_phoff + idx * ehdr->e_phentsize;
+
+	if (phdr->p_type != PT_LOAD) {
+		printf("unknown type %x\n", phdr->p_type);
+		return false;
+	}
+	// TODO overlap check
+	// TODO don't ignore flags
+	_syscall_memflag((void*)phdr->p_vaddr, phdr->p_memsz, MEMFLAG_PRESENT);
+	// TODO check that filesz <= memsz
+	memcpy((void*)phdr->p_vaddr, base + phdr->p_offset, phdr->p_filesz);
+	return true;
+}
+
+void elf_exec(void *base) {
+	struct Elf64_Ehdr *ehdr = base;
+	if (!valid_ehdr(ehdr)) return;
+	for (size_t phi = 0; phi < ehdr->e_phnum; phi++) {
+		if (!load_phdr(base, phi))
+			return;
+	}
+	((void(*)())ehdr->e_entry)();
+	_syscall_exit(1);
+}