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llext: make local relocations optional

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Some applications can decide to link their loadable objects for
exactly the same addresses, where they will be loaded. In those cases
local relocations aren't needed any more and can in fact break the
object if applied while the object is in a temporary storage. Add a
parameter to skip such local relocations.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
This commit is contained in:
Guennadi Liakhovetski 2023-09-26 13:02:25 +02:00 • committed by Anas Nashif
commit b0b4b0baa0
4 changed files with 42 additions and 18 deletions
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37
subsys/llext/llext.c
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@ -494,7 +494,8 @@ __weak void arch_elf_relocate_local(struct llext_loader *ldr, struct llext *ext,
{
}
static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr_t *shdr)
static void llext_link_plt(struct llext_loader *ldr, struct llext *ext,
elf_shdr_t *shdr, bool do_local)
{
unsigned int sh_cnt = shdr->sh_size / shdr->sh_entsize;
/*
@ -547,6 +548,11 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
uint32_t stt = ELF_ST_TYPE(sym_tbl.st_info);
uint32_t stb = ELF_ST_BIND(sym_tbl.st_info);
if (stt != STT_NOTYPE || sym_tbl.st_shndx != SHN_UNDEF) {
continue;
}
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
@ -555,9 +561,6 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
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)
continue;
const void *link_addr;
switch (stb) {
@ -574,16 +577,18 @@ static void llext_link_plt(struct llext_loader *ldr, struct llext *ext, elf_shdr
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;
break;
case STB_LOCAL:
arch_elf_relocate_local(ldr, ext, &rela, got_offset);
if (do_local) {
arch_elf_relocate_local(ldr, ext, &rela, got_offset);
}
}
LOG_DBG("symbol %s offset %#x r-offset %#x .text offset %#x stb %u",
name, got_offset,
rela.r_offset, ldr->sects[LLEXT_SECT_TEXT].sh_offset, stb);
}
}
@ -591,7 +596,7 @@ __weak void arch_elf_relocate(elf_rela_t *rel, uintptr_t opaddr, uintptr_t opval
{
}
static int llext_link(struct llext_loader *ldr, struct llext *ext)
static int llext_link(struct llext_loader *ldr, struct llext *ext, bool do_local)
{
uintptr_t loc = 0;
elf_shdr_t shdr;
@ -638,7 +643,7 @@ static int llext_link(struct llext_loader *ldr, struct llext *ext)
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);
llext_link_plt(ldr, ext, &shdr, do_local);
continue;
}
@ -724,7 +729,8 @@ static int llext_link(struct llext_loader *ldr, struct llext *ext)
/*
* Load a valid ELF as an extension
*/
static int do_llext_load(struct llext_loader *ldr, struct llext *ext)
static int do_llext_load(struct llext_loader *ldr, struct llext *ext,
struct llext_load_param *ldr_parm)
{
int ret = 0;
@ -793,7 +799,7 @@ static int do_llext_load(struct llext_loader *ldr, struct llext *ext)
}
LOG_DBG("Linking ELF...");
ret = llext_link(ldr, ext);
ret = llext_link(ldr, ext, ldr_parm ? ldr_parm->relocate_local : true);
if (ret != 0) {
LOG_ERR("Failed to link, ret %d", ret);
goto out;
@ -818,7 +824,8 @@ out:
return ret;
}
int llext_load(struct llext_loader *ldr, const char *name, struct llext **ext)
int llext_load(struct llext_loader *ldr, const char *name, struct llext **ext,
struct llext_load_param *ldr_parm)
{
int ret;
elf_ehdr_t ehdr;
@ -857,7 +864,7 @@ int llext_load(struct llext_loader *ldr, const char *name, struct llext **ext)
}
ldr->hdr = ehdr;
ret = do_llext_load(ldr, *ext);
ret = do_llext_load(ldr, *ext, ldr_parm);
break;
default:
LOG_ERR("Unsupported elf file type %x", ehdr.e_type);