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llext: add support for shared objects

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Add support for linking PIC shared object, which only require
linking, using their PLT and GOT lists and don't need any relocation
otherwise.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
This commit is contained in:
Guennadi Liakhovetski 2023-09-07 17:53:19 +02:00 • committed by Anas Nashif
commit d6a5a6e04c
1 changed files with 109 additions and 3 deletions
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112
subsys/llext/llext.c
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@ -446,6 +446,105 @@ static int llext_copy_symbols(struct llext_loader *ldr, struct llext *ext)
return 0;
}
/*
* Find the section, containing the supplied offset and return file offset for
* that value
*/
static size_t llext_file_offset(struct llext_loader *ldr, size_t offset)
{
unsigned int i;
for (i = 0; i < LLEXT_SECT_COUNT; i++)
if (ldr->sects[i].sh_addr <= offset &&
ldr->sects[i].sh_addr + ldr->sects[i].sh_size > offset)
return offset - ldr->sects[i].sh_addr + ldr->sects[i].sh_offset;
return offset;
}
static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr_t *shdr)
{
unsigned int sh_cnt = shdr->sh_size / shdr->sh_entsize;
/*
* CPU address where the .text section is stored, we use .text just as a
* reference point
*/
uint8_t *text = ext->mem[LLEXT_MEM_TEXT];
LOG_DBG("Found %p in PLT %u size %u cnt %u text %p",
(void *)llext_string(ldr, ext, LLEXT_MEM_SHSTRTAB, shdr->sh_name),
shdr->sh_type, shdr->sh_entsize, sh_cnt, (void *)text);
const elf_shdr_t *sym_shdr = ldr->sects + LLEXT_SECT_SYMTAB;
unsigned int sym_cnt = sym_shdr->sh_size / sym_shdr->sh_entsize;
for (unsigned int i = 0; i < sh_cnt; i++) {
elf_rela_t rela;
int ret = llext_seek(ldr, shdr->sh_offset + i * shdr->sh_entsize);
if (!ret) {
ret = llext_read(ldr, &rela, sizeof(rela));
}
if (ret < 0) {
LOG_ERR("PLT: failed to read RELA #%u, trying to continue", i);
continue;
}
/* Index in the symbol table */
unsigned int j = ELF32_R_SYM(rela.r_info);
if (j >= sym_cnt) {
LOG_WRN("PLT: idx %u >= %u", j, sym_cnt);
continue;
}
elf_sym_t sym_tbl;
ret = llext_seek(ldr, sym_shdr->sh_offset + j * sizeof(elf_sym_t));
if (!ret) {
ret = llext_read(ldr, &sym_tbl, sizeof(sym_tbl));
}
if (ret < 0) {
LOG_ERR("PLT: failed to read symbol table #%u RELA #%u, trying to continue",
j, i);
continue;
}
uint32_t stt = ELF_ST_TYPE(sym_tbl.st_info);
const char *name = llext_string(ldr, ext, LLEXT_MEM_STRTAB, sym_tbl.st_name);
/*
* Both r_offset and sh_addr are addresses for which the extension
* has been built.
*/
size_t got_offset = llext_file_offset(ldr, rela.r_offset) -
ldr->sects[LLEXT_SECT_TEXT].sh_offset;
if (stt == STT_NOTYPE && sym_tbl.st_shndx == SHN_UNDEF && name[0] != '\0') {
const void *link_addr = llext_find_sym(NULL, name);
if (!link_addr) {
LOG_WRN("PLT: cannot find idx %u name %s", j, name);
continue;
}
if (!rela.r_offset) {
LOG_WRN("PLT: zero offset idx %u name %s", j, name);
continue;
}
LOG_DBG("symbol %s offset %#x r-offset %#x .text offset %#x",
name, got_offset,
rela.r_offset, ldr->sects[LLEXT_SECT_TEXT].sh_offset);
/* Resolve the symbol */
*(const void **)(text + got_offset) = link_addr;
}
}
}
__weak void arch_elf_relocate(elf_rela_t *rel, uintptr_t opaddr, uintptr_t opval)
{
}
@ -486,12 +585,19 @@ static int llext_link(struct llext_loader *ldr, struct llext *ext)
if (strcmp(name, ".rel.text") == 0 ||
strcmp(name, ".rela.text") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_TEXT];
} else if (strcmp(name, ".rel.bss") == 0) {
} else if (strcmp(name, ".rel.bss") == 0 ||
strcmp(name, ".rela.bss") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_BSS];
} else if (strcmp(name, ".rel.rodata") == 0) {
} else if (strcmp(name, ".rel.rodata") == 0 ||
strcmp(name, ".rela.rodata") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_RODATA];
} else if (strcmp(name, ".rel.data") == 0) {
} else if (strcmp(name, ".rel.data") == 0 ||
strcmp(name, ".rela.data") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_DATA];
} else if (strcmp(name, ".rela.plt") == 0 ||
strcmp(name, ".rela.dyn") == 0) {
llext_link_plt(ldr, ext, &shdr);
continue;
}
LOG_DBG("relocation section %s (%d) linked to section %d has %d relocations",