init: compile as an elf

1 files changed, 42 insertions, 0 deletions

diff --git a/src/user/lib/elfreloc.c b/src/user/lib/elfreloc.c
new file mode 100644
index 0000000..550fe97
--- /dev/null
+++ b/src/user/lib/elfreloc.c
@@ -0,0 +1,42 @@
+#include <user/lib/elf.h>
+#include <user/lib/stdlib.h>
+
+__attribute__((visibility("hidden")))
+extern struct Elf64_Dyn _DYNAMIC[];
+
+__attribute__((visibility("hidden")))
+extern char _image_base[];
+
+static struct Elf64_Dyn *dyn_gettag(Elf64_Xword tag) {
+	for (size_t i = 0;; i++) {
+		if (_DYNAMIC[i].d_tag == tag) return &_DYNAMIC[i];
+		if (_DYNAMIC[i].d_tag == DT_NULL) return NULL;
+	}
+}
+
+void elf_selfreloc(void) {
+	// TODO DT_REL
+	if (dyn_gettag(DT_PLTGOT) || dyn_gettag(DT_JMPREL)) {
+		_klogf("elf: unimplemented tag in _DYNAMIC\n");
+	}
+
+	struct Elf64_Dyn *rela_tag = dyn_gettag(DT_RELA);
+	if (rela_tag) {
+		/* not checking pointer validity,
+		 * crashing on an invalid elf is fine */
+		size_t relasz = dyn_gettag(DT_RELASZ)->d_val;
+		size_t relaent = dyn_gettag(DT_RELAENT)->d_val;
+		for (size_t o = 0; o < relasz; o += relaent) {
+			struct Elf64_Rela *r = (void*)_image_base + rela_tag->d_ptr + o;
+			uintptr_t *target = (void*)_image_base + r->r_offset;
+
+			switch (ELF64_R_TYPE(r->r_info)) {
+				case R_X86_64_RELATIVE:
+					*target = (uintptr_t)&_image_base + r->r_addend;
+					break;
+				default:
+					_klogf("elf: unsupported relocation type\n");
+			}
+		}
+	}
+}