LLEXT: fix advanced uses of detached sections
When detached sections are used, STB_GLOBAL relocations also have to be processed depending on the relocation type. This commit unified STB_GLOBAL and STB_LOCAL flows by making them use the same relocation type parser, adds support for R_XTENSA_GLOB_DAT and R_XTENSA_JMP_SLOT type relocations on Xtensa and fixes STT_SECTION address calculation for such sections. Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
This commit is contained in:
Guennadi Liakhovetski
Anas Nashif
parent
2b3666109e
commit
4f0cb90c59
3 changed files with 147 additions and 54 deletions
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@ -12,6 +12,16 @@
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LOG_MODULE_DECLARE(llext, CONFIG_LLEXT_LOG_LEVEL);
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/*
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* ELF relocation tables on Xtensa contain relocations of different types. They
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* specify how the relocation should be performed. Which relocations are used
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* depends on the type of the ELF object (e.g. shared or partially linked
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* object), structure of the object (single or multiple source files), compiler
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* flags used (e.g. -fPIC), etc. Also not all relocation table entries should be
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* acted upon. Some of them describe relocations that have already been
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* resolved by the linker. We have to distinguish them from actionable
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* relocations and only need to handle the latter ones.
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*/
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#define R_XTENSA_NONE 0
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#define R_XTENSA_32 1
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#define R_XTENSA_RTLD 2
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@ -19,71 +29,126 @@ LOG_MODULE_DECLARE(llext, CONFIG_LLEXT_LOG_LEVEL);
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#define R_XTENSA_JMP_SLOT 4
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#define R_XTENSA_RELATIVE 5
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#define R_XTENSA_PLT 6
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#define R_XTENSA_ASM_EXPAND 11
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#define R_XTENSA_SLOT0_OP 20
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static void xtensa_elf_relocate(struct llext_loader *ldr, struct llext *ext,
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const elf_rela_t *rel, uint8_t *text, uintptr_t addr,
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uint8_t *loc, int type, uint32_t stb)
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{
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elf_word *got_entry = (elf_word *)loc;
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switch (type) {
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case R_XTENSA_RELATIVE:
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/* Relocate a local symbol: Xtensa specific. Seems to only be used with PIC */
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*got_entry += (uintptr_t)text - addr;
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break;
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case R_XTENSA_GLOB_DAT:
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case R_XTENSA_JMP_SLOT:
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if (stb == STB_GLOBAL) {
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*got_entry = addr;
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}
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break;
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case R_XTENSA_32:
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/* Used for both LOCAL and GLOBAL bindings */
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*got_entry += addr;
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break;
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case R_XTENSA_SLOT0_OP:
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/* Apparently only actionable with LOCAL bindings */
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;
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elf_sym_t rsym;
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int ret = llext_seek(ldr, ldr->sects[LLEXT_MEM_SYMTAB].sh_offset +
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ELF_R_SYM(rel->r_info) * sizeof(elf_sym_t));
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if (!ret) {
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ret = llext_read(ldr, &rsym, sizeof(elf_sym_t));
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}
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if (ret) {
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LOG_ERR("Failed to read a symbol table entry, LLEXT linking might fail.");
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return;
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}
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/*
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* So far in all observed use-cases
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* llext_loaded_sect_ptr(ldr, ext, rsym.st_shndx) was already
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* available as the "addr" argument of this function, supplied
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* by arch_elf_relocate_local() from its non-STT_SECTION branch.
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*/
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uintptr_t link_addr = (uintptr_t)llext_loaded_sect_ptr(ldr, ext, rsym.st_shndx) +
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rsym.st_value + rel->r_addend;
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ssize_t value = (link_addr - (((uintptr_t)got_entry + 3) & ~3)) >> 2;
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/* Check the opcode */
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if ((loc[0] & 0xf) == 1 && !loc[1] && !loc[2]) {
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/* L32R: low nibble is 1 */
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loc[1] = value & 0xff;
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loc[2] = (value >> 8) & 0xff;
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} else if ((loc[0] & 0xf) == 5 && !(loc[0] & 0xc0) && !loc[1] && !loc[2]) {
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/* CALLn: low nibble is 5 */
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loc[0] = (loc[0] & 0x3f) | ((value << 6) & 0xc0);
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loc[1] = (value >> 2) & 0xff;
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loc[2] = (value >> 10) & 0xff;
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} else {
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LOG_DBG("%p: unhandled OPC or no relocation %02x%02x%02x inf %#x offs %#x",
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(void *)loc, loc[2], loc[1], loc[0],
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rel->r_info, rel->r_offset);
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break;
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}
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break;
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case R_XTENSA_ASM_EXPAND:
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/* Nothing to do */
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break;
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default:
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LOG_DBG("Unsupported relocation type %u", type);
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return;
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}
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LOG_DBG("Applied relocation to %#x type %u at %p",
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*(uint32_t *)((uintptr_t)got_entry & ~3), type, (void *)got_entry);
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}
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/**
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* @brief Architecture specific function for relocating shared elf
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*
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* Elf files contain a series of relocations described in multiple sections.
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* These relocation instructions are architecture specific and each architecture
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* supporting modules must implement this.
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* @brief Architecture specific function for STB_LOCAL ELF relocations
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*/
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void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
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const elf_rela_t *rel, const elf_sym_t *sym, size_t got_offset)
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void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
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const elf_sym_t *sym, size_t got_offset,
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const struct llext_load_param *ldr_parm)
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{
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uint8_t *text = ext->mem[LLEXT_MEM_TEXT];
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uint8_t *loc = text + got_offset;
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int type = ELF32_R_TYPE(rel->r_info);
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elf_word *got_entry = (elf_word *)(text + got_offset);
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uintptr_t sh_addr;
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if (ELF_ST_TYPE(sym->st_info) == STT_SECTION) {
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elf_shdr_t *shdr = llext_peek(ldr, ldr->hdr.e_shoff +
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sym->st_shndx * ldr->hdr.e_shentsize);
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sh_addr = shdr->sh_addr ? : (uintptr_t)llext_peek(ldr, shdr->sh_offset);
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sh_addr = shdr->sh_addr &&
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(!ldr_parm->section_detached || !ldr_parm->section_detached(shdr)) ?
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shdr->sh_addr : (uintptr_t)llext_peek(ldr, shdr->sh_offset);
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} else {
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sh_addr = ldr->sects[LLEXT_MEM_TEXT].sh_addr;
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}
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switch (type) {
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case R_XTENSA_RELATIVE:
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/* Relocate a local symbol: Xtensa specific */
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*got_entry += (uintptr_t)text - sh_addr;
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break;
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case R_XTENSA_32:
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*got_entry += sh_addr;
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break;
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case R_XTENSA_SLOT0_OP:
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;
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uint8_t *opc = (uint8_t *)got_entry;
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xtensa_elf_relocate(ldr, ext, rel, text, sh_addr, loc, type, ELF_ST_BIND(sym->st_info));
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}
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/* Check the opcode: is this an L32R? And does it have to be relocated? */
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if ((opc[0] & 0xf) != 1 || opc[1] || opc[2])
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break;
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/**
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* @brief Architecture specific function for STB_GLOBAL ELF relocations
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*/
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void arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext, const elf_rela_t *rel,
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const elf_sym_t *sym, size_t got_offset, const void *link_addr)
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{
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uint8_t *text = ext->mem[LLEXT_MEM_TEXT];
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elf_word *got_entry = (elf_word *)(text + got_offset);
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int type = ELF32_R_TYPE(rel->r_info);
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elf_sym_t rsym;
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int ret = llext_seek(ldr, ldr->sects[LLEXT_MEM_SYMTAB].sh_offset +
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ELF_R_SYM(rel->r_info) * sizeof(elf_sym_t));
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if (!ret) {
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ret = llext_read(ldr, &rsym, sizeof(elf_sym_t));
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}
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if (ret)
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return;
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uintptr_t link_addr = (uintptr_t)llext_loaded_sect_ptr(ldr, ext, rsym.st_shndx) +
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rsym.st_value + rel->r_addend;
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ssize_t value = (link_addr - (((uintptr_t)got_entry + 3) & ~3)) >> 2;
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opc[1] = value & 0xff;
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opc[2] = (value >> 8) & 0xff;
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break;
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default:
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LOG_DBG("unsupported relocation type %u", type);
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return;
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/* For global relocations we expect the initial value for R_XTENSA_RELATIVE to be zero */
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if (type == R_XTENSA_RELATIVE && *got_entry) {
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LOG_WRN("global: non-zero relative value %#x", *got_entry);
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}
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LOG_DBG("relocation to %#x type %u at %p", *got_entry, type, (void *)got_entry);
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xtensa_elf_relocate(ldr, ext, rel, text, (uintptr_t)link_addr, (uint8_t *)got_entry, type,
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ELF_ST_BIND(sym->st_info));
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}
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@ -339,16 +339,31 @@ int arch_elf_relocate(elf_rela_t *rel, uintptr_t loc,
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ssize_t llext_find_section(struct llext_loader *loader, const char *search_name);
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/**
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* @brief Architecture specific function for updating addresses via relocation table
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* @brief Architecture specific function for local binding relocations
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*
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* @param[in] loader Extension loader data and context
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* @param[in] ext Extension to call function in
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* @param[in] rel Relocation data provided by elf
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* @param[in] sym Corresponding symbol table entry
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* @param[in] got_offset Offset within a relocation table
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* @param[in] got_offset Offset within a relocation table or in the code
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* @param[in] ldr_parm Loader parameters
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*/
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void arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext,
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const elf_rela_t *rel, const elf_sym_t *sym, size_t got_offset);
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void arch_elf_relocate_local(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
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const elf_sym_t *sym, size_t got_offset,
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const struct llext_load_param *ldr_parm);
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/**
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* @brief Architecture specific function for global binding relocations
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*
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* @param[in] loader Extension loader data and context
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* @param[in] ext Extension to call function in
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* @param[in] rel Relocation data provided by elf
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* @param[in] sym Corresponding symbol table entry
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* @param[in] got_offset Offset within a relocation table or in the code
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* @param[in] link_addr target address for table-based relocations
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*/
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void arch_elf_relocate_global(struct llext_loader *loader, struct llext *ext, const elf_rela_t *rel,
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const elf_sym_t *sym, size_t got_offset, const void *link_addr);
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/**
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* @}
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@ -33,7 +33,14 @@ __weak int arch_elf_relocate(elf_rela_t *rel, uintptr_t loc,
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}
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__weak void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
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const elf_rela_t *rel, const elf_sym_t *sym, size_t got_offset)
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const elf_rela_t *rel, const elf_sym_t *sym, size_t got_offset,
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const struct llext_load_param *ldr_parm)
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{
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}
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__weak void arch_elf_relocate_global(struct llext_loader *ldr, struct llext *ext,
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const elf_rela_t *rel, const elf_sym_t *sym, size_t got_offset,
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const void *link_addr)
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{
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}
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@ -249,11 +256,12 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
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}
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/* Resolve the symbol */
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*(const void **)(text + got_offset) = link_addr;
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arch_elf_relocate_global(ldr, ext, &rela, &sym, got_offset, link_addr);
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break;
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case STB_LOCAL:
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if (ldr_parm->relocate_local) {
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arch_elf_relocate_local(ldr, ext, &rela, &sym, got_offset);
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arch_elf_relocate_local(ldr, ext, &rela, &sym, got_offset,
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ldr_parm);
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}
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}
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@ -327,6 +335,11 @@ int llext_link(struct llext_loader *ldr, struct llext *ext, const struct llext_l
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strcmp(name, ".rela.dyn") == 0) {
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tgt = NULL;
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} else {
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/*
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* Entries in .rel.X and .rela.X sections describe references in
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* section .X to local or global symbols. They point to entries
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* in the symbol table, describing respective symbols
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*/
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tgt = ldr->sect_hdrs + shdr->sh_info;
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}
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