diff options
| -rw-r--r-- | util/cbfstool/elfheaders.c | 319 | ||||
| -rw-r--r-- | util/cbfstool/elfparsing.h | 31 |
2 files changed, 350 insertions, 0 deletions
diff --git a/util/cbfstool/elfheaders.c b/util/cbfstool/elfheaders.c index f3ed05c105..d217aac0cd 100644 --- a/util/cbfstool/elfheaders.c +++ b/util/cbfstool/elfheaders.c @@ -625,3 +625,322 @@ elf_headers(const struct buffer *pinput, return 0; } + +/* ELF Writing Support + * + * The ELF file is written according to the following layout: + * +------------------+ + * | ELF Header | + * +------------------+ + * | Section Headers | + * +------------------+ + * | Program Headers | + * +------------------+ + * | String table | + * +------------------+ <- 4KiB Aligned + * | Code/Data | + * +------------------+ + */ + +/* Arbitray maximum number of sections. */ +#define MAX_SECTIONS 16 +struct elf_writer_section { + Elf64_Shdr shdr; + struct buffer content; + const char *name; +}; + +struct elf_writer +{ + Elf64_Ehdr ehdr; + struct xdr *xdr; + size_t num_secs; + struct elf_writer_section sections[MAX_SECTIONS]; + Elf64_Phdr *phdrs; + struct elf_writer_section *shstrtab; + int bit64; +}; + +struct elf_writer *elf_writer_init(const Elf64_Ehdr *ehdr) +{ + struct elf_writer *ew; + Elf64_Shdr shdr; + struct buffer empty_buffer; + + if (!iself(ehdr)) + return NULL; + + ew = calloc(1, sizeof(*ew)); + + memcpy(&ew->ehdr, ehdr, sizeof(ew->ehdr)); + + ew->bit64 = ew->ehdr.e_ident[EI_CLASS] == ELFCLASS64; + + /* Set the endinan ops. */ + if (ew->ehdr.e_ident[EI_DATA] == ELFDATA2MSB) + ew->xdr = &xdr_be; + else + ew->xdr = &xdr_le; + + /* Reset count and offsets */ + ew->ehdr.e_phoff = 0; + ew->ehdr.e_shoff = 0; + ew->ehdr.e_shnum = 0; + ew->ehdr.e_phnum = 0; + + memset(&empty_buffer, 0, sizeof(empty_buffer)); + memset(&shdr, 0, sizeof(shdr)); + + /* Add SHT_NULL section header. */ + shdr.sh_type = SHT_NULL; + elf_writer_add_section(ew, &shdr, &empty_buffer, NULL); + + /* Add section header string table and maintain reference to it. */ + shdr.sh_type = SHT_STRTAB; + elf_writer_add_section(ew, &shdr, &empty_buffer, ".shstrtab"); + ew->ehdr.e_shstrndx = ew->num_secs - 1; + ew->shstrtab = &ew->sections[ew->ehdr.e_shstrndx]; + + return ew; +} + +/* + * Clean up any internal state represented by ew. Aftewards the elf_writer + * is invalid. + */ +void elf_writer_destroy(struct elf_writer *ew) +{ + if (ew->phdrs != NULL) + free(ew->phdrs); + free(ew); +} + +/* + * Add a section to the ELF file. Section type, flags, and memsize are + * maintained from the passed in Elf64_Shdr. The buffer represents the + * content of the section while the name is the name of section itself. + * Returns < 0 on error, 0 on success. + */ +int elf_writer_add_section(struct elf_writer *ew, const Elf64_Shdr *shdr, + struct buffer *contents, const char *name) +{ + struct elf_writer_section *newsh; + + if (ew->num_secs == MAX_SECTIONS) + return -1; + + newsh = &ew->sections[ew->num_secs]; + ew->num_secs++; + + memcpy(&newsh->shdr, shdr, sizeof(newsh->shdr)); + newsh->shdr.sh_offset = 0; + + newsh->name = name; + if (contents != NULL) + buffer_clone(&newsh->content, contents); + + return 0; +} + +static void ehdr_write(struct elf_writer *ew, struct buffer *m) +{ + int i; + + for (i = 0; i < EI_NIDENT; i++) + ew->xdr->put8(m, ew->ehdr.e_ident[i]); + ew->xdr->put16(m, ew->ehdr.e_type); + ew->xdr->put16(m, ew->ehdr.e_machine); + ew->xdr->put32(m, ew->ehdr.e_version); + if (ew->bit64) { + ew->xdr->put64(m, ew->ehdr.e_entry); + ew->xdr->put64(m, ew->ehdr.e_phoff); + ew->xdr->put64(m, ew->ehdr.e_shoff); + } else { + ew->xdr->put32(m, ew->ehdr.e_entry); + ew->xdr->put32(m, ew->ehdr.e_phoff); + ew->xdr->put32(m, ew->ehdr.e_shoff); + } + ew->xdr->put32(m, ew->ehdr.e_flags); + ew->xdr->put16(m, ew->ehdr.e_ehsize); + ew->xdr->put16(m, ew->ehdr.e_phentsize); + ew->xdr->put16(m, ew->ehdr.e_phnum); + ew->xdr->put16(m, ew->ehdr.e_shentsize); + ew->xdr->put16(m, ew->ehdr.e_shnum); + ew->xdr->put16(m, ew->ehdr.e_shstrndx); +} + +static void shdr_write(struct elf_writer *ew, size_t n, struct buffer *m) +{ + struct xdr *xdr = ew->xdr; + int bit64 = ew->bit64; + struct elf_writer_section *sec = &ew->sections[n]; + Elf64_Shdr *shdr = &sec->shdr; + + xdr->put32(m, shdr->sh_name); + xdr->put32(m, shdr->sh_type); + xdr->put32(m, shdr->sh_flags); + if (bit64) { + xdr->put64(m, shdr->sh_addr); + xdr->put64(m, shdr->sh_offset); + xdr->put64(m, shdr->sh_size); + xdr->put32(m, shdr->sh_link); + xdr->put32(m, shdr->sh_info); + xdr->put64(m, shdr->sh_addralign); + xdr->put64(m, shdr->sh_entsize); + } else { + xdr->put32(m, shdr->sh_addr); + xdr->put32(m, shdr->sh_offset); + xdr->put32(m, shdr->sh_size); + xdr->put32(m, shdr->sh_link); + xdr->put32(m, shdr->sh_info); + xdr->put32(m, shdr->sh_addralign); + xdr->put32(m, shdr->sh_entsize); + } +} + +static void +phdr_write(struct elf_writer *ew, struct buffer *m, Elf64_Phdr *phdr) +{ + if (ew->bit64) { + ew->xdr->put32(m, phdr->p_type); + ew->xdr->put32(m, phdr->p_flags); + ew->xdr->put64(m, phdr->p_offset); + ew->xdr->put64(m, phdr->p_vaddr); + ew->xdr->put64(m, phdr->p_paddr); + ew->xdr->put64(m, phdr->p_filesz); + ew->xdr->put64(m, phdr->p_memsz); + ew->xdr->put64(m, phdr->p_align); + } else { + ew->xdr->put32(m, phdr->p_type); + ew->xdr->put32(m, phdr->p_offset); + ew->xdr->put32(m, phdr->p_vaddr); + ew->xdr->put32(m, phdr->p_paddr); + ew->xdr->put32(m, phdr->p_filesz); + ew->xdr->put32(m, phdr->p_memsz); + ew->xdr->put32(m, phdr->p_flags); + ew->xdr->put32(m, phdr->p_align); + } + +} + +/* + * Serialize the ELF file to the output buffer. Return < 0 on error, + * 0 on success. + */ +int elf_writer_serialize(struct elf_writer *ew, struct buffer *out) +{ + Elf64_Half i; + Elf64_Xword metadata_size; + Elf64_Xword program_size; + Elf64_Off shstroffset; + size_t shstrlen; + struct buffer metadata; + struct buffer phdrs; + struct buffer data; + struct buffer *strtab; + + INFO("Writing %zu sections.\n", ew->num_secs); + + /* Determine size of sections to be written. */ + program_size = 0; + /* Start with 1 byte for first byte of section header string table. */ + shstrlen = 1; + for (i = 0; i < ew->num_secs; i++) { + struct elf_writer_section *sec = &ew->sections[i]; + + if (sec->shdr.sh_flags & SHF_ALLOC) + ew->ehdr.e_phnum++; + + program_size += buffer_size(&sec->content); + + /* Keep track of the length sections' names. */ + if (sec->name != NULL) { + sec->shdr.sh_name = shstrlen; + shstrlen += strlen(sec->name) + 1; + } + } + ew->ehdr.e_shnum = ew->num_secs; + metadata_size = 0; + metadata_size += ew->ehdr.e_ehsize; + metadata_size += ew->ehdr.e_shnum * ew->ehdr.e_shentsize; + metadata_size += ew->ehdr.e_phnum * ew->ehdr.e_phentsize; + shstroffset = metadata_size; + /* Align up section header string size and metadata size to 4KiB */ + metadata_size = ALIGN(metadata_size + shstrlen, 4096); + + if (buffer_create(out, metadata_size + program_size, "elfout")) { + ERROR("Could not create output buffer for ELF.\n"); + return -1; + } + + INFO("Created %zu output buffer for ELF file.\n", buffer_size(out)); + + /* + * Write out ELF header. Section headers come right after ELF header + * followed by the program headers. Buffers need to be created first + * to do the writing. + */ + ew->ehdr.e_shoff = ew->ehdr.e_ehsize; + ew->ehdr.e_phoff = ew->ehdr.e_shoff + + ew->ehdr.e_shnum * ew->ehdr.e_shentsize; + + buffer_splice(&metadata, out, 0, metadata_size); + buffer_splice(&phdrs, out, ew->ehdr.e_phoff, + ew->ehdr.e_phnum * ew->ehdr.e_phentsize); + buffer_splice(&data, out, metadata_size, program_size); + /* Set up the section header string table contents. */ + strtab = &ew->shstrtab->content; + buffer_splice(strtab, out, shstroffset, shstrlen); + ew->shstrtab->shdr.sh_size = shstrlen; + + /* Reset current locations. */ + buffer_set_size(&metadata, 0); + buffer_set_size(&data, 0); + buffer_set_size(&phdrs, 0); + buffer_set_size(strtab, 0); + + /* ELF Header */ + ehdr_write(ew, &metadata); + + /* Write out section headers, section strings, section content, and + * program headers. */ + ew->xdr->put8(strtab, 0); + for (i = 0; i < ew->num_secs; i++) { + Elf64_Phdr phdr; + struct elf_writer_section *sec = &ew->sections[i]; + + /* Update section offsets. Be sure to not update SHT_NULL. */ + if (sec == ew->shstrtab) + sec->shdr.sh_offset = shstroffset; + else if (i != 0) + sec->shdr.sh_offset = buffer_size(&data) + + metadata_size; + shdr_write(ew, i, &metadata); + + /* Add section name to string table. */ + if (sec->name != NULL) + bputs(strtab, sec->name, strlen(sec->name) + 1); + + if (!(sec->shdr.sh_flags & SHF_ALLOC)) + continue; + + bputs(&data, buffer_get(&sec->content), + buffer_size(&sec->content)); + + phdr.p_type = PT_LOAD; + phdr.p_offset = sec->shdr.sh_offset; + phdr.p_vaddr = sec->shdr.sh_addr; + phdr.p_paddr = sec->shdr.sh_addr; + phdr.p_filesz = buffer_size(&sec->content); + phdr.p_memsz = sec->shdr.sh_size; + phdr.p_flags = 0; + if (sec->shdr.sh_flags & SHF_EXECINSTR) + phdr.p_flags |= PF_X | PF_R; + if (sec->shdr.sh_flags & SHF_WRITE) + phdr.p_flags |= PF_W; + phdr.p_align = sec->shdr.sh_addralign; + phdr_write(ew, &phdrs, &phdr); + } + + return 0; +} diff --git a/util/cbfstool/elfparsing.h b/util/cbfstool/elfparsing.h index 113301aae2..048d31aa2b 100644 --- a/util/cbfstool/elfparsing.h +++ b/util/cbfstool/elfparsing.h @@ -74,4 +74,35 @@ elf_headers(const struct buffer *pinput, Elf64_Phdr **pphdr, Elf64_Shdr **pshdr); +/* ELF writing support. */ +struct elf_writer; + +/* + * Initialize a new ELF writer. Deafult machine type, endianness, etc is + * copied from the passed in Elf64_Ehdr. Returns NULL on failure, valid + * pointer on success. + */ +struct elf_writer *elf_writer_init(const Elf64_Ehdr *ehdr); + +/* + * Clean up any internal state represented by ew. Aftewards the elf_writer + * is invalid. + */ +void elf_writer_destroy(struct elf_writer *ew); + +/* + * Add a section to the ELF file. Section type, flags, and memsize are + * maintained from the passed in Elf64_Shdr. The buffer represents the + * content of the section while the name is the name of section itself. + * Returns < 0 on error, 0 on success. + */ +int elf_writer_add_section(struct elf_writer *ew, const Elf64_Shdr *shdr, + struct buffer *contents, const char *name); + +/* + * Serialize the ELF file to the output buffer. Return < 0 on error, + * 0 on success. + */ +int elf_writer_serialize(struct elf_writer *ew, struct buffer *out); + #endif /* ELFPARSING_H */ |