Hi, On 1/5/26 12:26 PM, Sascha Hauer wrote: > Implement elf_load_inplace() to apply dynamic relocations to an ELF binary > that is already loaded in memory. Unlike elf_load(), this function does not > allocate memory or copy segments - it only modifies the existing image in > place. > > This is useful for self-relocating loaders or when the ELF has been loaded > by external means (e.g., firmware or another bootloader).
Nice. This is more elegant than what I came up with (compressing every segment separately). :) > For ET_DYN (position-independent) binaries, the relocation offset is > calculated relative to the first executable PT_LOAD segment (.text section), > taking into account the difference between the segment's virtual address > and its file offset. While this may be true for barebox proper, I think in the general case, we need to iterate over all segments and take the lowest address. The first executable PT_LOAD shouldn't have a special significance in this case. > > The entry point is also adjusted to point to the relocated image. > > Signed-off-by: Sascha Hauer <[email protected]> > Co-Authored-By: Claude Sonnet 4.5 <[email protected]> > --- > common/elf.c | 152 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > include/elf.h | 8 ++++ > 2 files changed, 160 insertions(+) > > diff --git a/common/elf.c b/common/elf.c > index > fc2949c285ebb0c0740c68c551926da8d0bb8637..565b283b694773727ef77917cfd8c1d4ee83a8d1 > 100644 > --- a/common/elf.c > +++ b/common/elf.c > @@ -531,3 +531,155 @@ void elf_close(struct elf_image *elf) > > free(elf); > } > + > +static void *elf_find_dynamic_inplace(struct elf_image *elf) const void * > +{ > + void *buf = elf->hdr_buf; > + void *phdr = buf + elf_hdr_e_phoff(elf, buf); > + int i; > + > + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { > + if (elf_phdr_p_type(elf, phdr) == PT_DYNAMIC) { > + u64 offset = elf_phdr_p_offset(elf, phdr); > + /* For in-place binary, PT_DYNAMIC is at hdr_buf + > offset */ > + return elf->hdr_buf + offset; > + } > + phdr += elf_size_of_phdr(elf); > + } > + > + return NULL; /* No PT_DYNAMIC segment */ > +} > + > +/** > + * elf_load_inplace() - Apply dynamic relocations to an ELF binary in place > + * @elf: ELF image previously opened with elf_open_binary() > + * > + * This function applies dynamic relocations to an ELF binary that is already > + * loaded at its target address in memory. Unlike elf_load(), this does not > + * allocate memory or copy segments - it only modifies the existing image. > + * > + * This is useful for self-relocating loaders or when the ELF has been loaded > + * by external means (e.g., loaded by firmware or another bootloader). > + * > + * The ELF image must have been previously opened with elf_open_binary(). > + * > + * For ET_DYN (position-independent) binaries, the relocation offset is > + * calculated relative to the first executable PT_LOAD segment (.text > section). > + * > + * For ET_EXEC binaries, no relocation is applied as they are expected to > + * be at their link-time addresses. > + * > + * Returns: 0 on success, negative error code on failure > + */ > +int elf_load_inplace(struct elf_image *elf) > +{ > + void *dyn_seg; > + void *buf, *phdr; > + void *elf_buf; > + int i, ret; > + > + buf = elf->hdr_buf; > + elf_buf = elf->hdr_buf; > + > + /* > + * First pass: Clear BSS segments (p_memsz > p_filesz). > + * This must be done before relocations as uninitialized data > + * must be zeroed per C standard. > + */ > + phdr = buf + elf_hdr_e_phoff(elf, buf); > + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { > + if (elf_phdr_p_type(elf, phdr) == PT_LOAD) { > + u64 p_offset = elf_phdr_p_offset(elf, phdr); > + u64 p_filesz = elf_phdr_p_filesz(elf, phdr); > + u64 p_memsz = elf_phdr_p_memsz(elf, phdr); > + > + /* Clear BSS (uninitialized data) */ > + if (p_filesz < p_memsz) { > + void *bss_start = elf_buf + p_offset + p_filesz; > + size_t bss_size = p_memsz - p_filesz; > + memset(bss_start, 0x00, bss_size); How can this be done in-place? If this is padding to get to a page boundary, I would assume it's already zero. If it goes beyond a page, this will overwrite follow-up segments wouldn't it? I also find bss_ an unforunate name here as this is applied to all segments. > + if (elf->type == ET_DYN) { > + u64 text_vaddr = 0; > + u64 text_offset = 0; > + bool found_text = false; > + > + /* Find first executable PT_LOAD segment (.text) */ As mentioned, we should rather get the lowest address across all segments. > + /* Apply architecture-specific relocations */ > + ret = elf_apply_relocations(elf, dyn_seg); Should I upstream my relocate_image changes that reuse the relocate_to_current_adr() code and you rebase on top? > + if (ret) { > + pr_err("In-place relocation failed: %d\n", ret); > + goto out; return ret; directly here and elsewhere in this function. Cheers, Ahmad -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
