From 3badc5ac30fcc0836a2604146788158b16b64f2d Mon Sep 17 00:00:00 2001 From: dzwdz Date: Sat, 23 Jul 2022 18:20:06 +0200 Subject: init: compile as an elf --- src/user/lib/elfreloc.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 src/user/lib/elfreloc.c (limited to 'src/user/lib/elfreloc.c') 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 +#include + +__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"); + } + } + } +} -- cgit v1.2.3