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llext: load: memcpy section header #97993

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merged 1 commit into from
Oct 23, 2025
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llext: load: memcpy section header #97993

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8 changes: 4 additions & 4 deletions subsys/llext/llext_load.c
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Original file line number Diff line number Diff line change
Expand Up @@ -177,24 +177,24 @@ static int llext_find_tables(struct llext_loader *ldr, struct llext *ext)

if (shdr->sh_type == SHT_SYMTAB && ldr->hdr.e_type == ET_REL) {
LOG_DBG("symtab at %d", i);
ldr->sects[LLEXT_MEM_SYMTAB] = *shdr;
memcpy(&ldr->sects[LLEXT_MEM_SYMTAB], shdr, sizeof(*shdr));
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@lyakh lyakh Oct 27, 2025

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wow, interesting. Is this compiler-specific? IIRC I've seen a structure assignment being replaced by the compiler with a memcpy builtin. That implementation shouldn't assume any alignment. And in general - as long as there's no alignment attribute, is it valid to assume any such alignment? I think structures are defined to be aligned in arrays, but stand-alone - I wasn't aware of such restrictions at least

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@teburd teburd Oct 27, 2025

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We've ran into similar issues with mipi sys-t logging in the past which, yes, when derefencing arbitrary pointers and applying assignment would result in unaligned access faults just like this.

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@lyakh lyakh Oct 28, 2025

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@teburd but that depends on the type of the pointer. If it's a char * certainly no alignment is needed. For a 2-byte type a two-byte alignment is needed and so on. And for a structure? Even the fact that the linker placed a section header above without a 4-byte alignment suggests, that it's valid. And then the compiler fails to generate code to read it. Interesting.

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@JordanYates JordanYates Oct 28, 2025

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Even the fact that the linker placed a section header above without a 4-byte alignment suggests, that it's valid

Its not clear to me why the section header should have any alignment requirements, its a binary data structure, not executable code. Even if it did have an alignment, what should that be? A uint32_t alignment, that would work fine for the 32 bit targets, would still have an incorrect alignment on 64 bit platforms.

ldr->sect_map[i].mem_idx = LLEXT_MEM_SYMTAB;
strtab_ndx = shdr->sh_link;
table_cnt++;
} else if (shdr->sh_type == SHT_DYNSYM && ldr->hdr.e_type == ET_DYN) {
LOG_DBG("dynsym at %d", i);
ldr->sects[LLEXT_MEM_SYMTAB] = *shdr;
memcpy(&ldr->sects[LLEXT_MEM_SYMTAB], shdr, sizeof(*shdr));
ldr->sect_map[i].mem_idx = LLEXT_MEM_SYMTAB;
strtab_ndx = shdr->sh_link;
table_cnt++;
} else if (shdr->sh_type == SHT_STRTAB && i == shstrtab_ndx) {
LOG_DBG("shstrtab at %d", i);
ldr->sects[LLEXT_MEM_SHSTRTAB] = *shdr;
memcpy(&ldr->sects[LLEXT_MEM_SHSTRTAB], shdr, sizeof(*shdr));
ldr->sect_map[i].mem_idx = LLEXT_MEM_SHSTRTAB;
table_cnt++;
} else if (shdr->sh_type == SHT_STRTAB && i == strtab_ndx) {
LOG_DBG("strtab at %d", i);
ldr->sects[LLEXT_MEM_STRTAB] = *shdr;
memcpy(&ldr->sects[LLEXT_MEM_STRTAB], shdr, sizeof(*shdr));
ldr->sect_map[i].mem_idx = LLEXT_MEM_STRTAB;
table_cnt++;
}
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