From: Eli Bendersky Date: Sun, 25 Sep 2011 02:37:30 +0000 (+0300) Subject: added a utils folder with elf_creator.c X-Git-Tag: v0.10~91 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=447763c305b69a1edea508ee05ec30c694f863ab;p=pyelftools.git added a utils folder with elf_creator.c --- diff --git a/utils/Makefile b/utils/Makefile new file mode 100644 index 0000000..fd44b8e --- /dev/null +++ b/utils/Makefile @@ -0,0 +1,18 @@ +CFLAGS = -Wall --std=c99 +# This is where `make install` from libelf places its stuff +LIBELF_HEADERS = /usr/local/include/libelf/ +LIBELF_LIBS = /usr/local/lib/ + +all: elf_creator + +elf_creator: elf_creator.c + gcc $(CFLAGS) -o elf_creator elf_creator.c \ + -I$(LIBELF_HEADERS) -L$(LIBELF_LIBS) -Wl,-rpath,$(LIBELF_LIBS) -lelf + +clean: + rm -f *.o + rm -f *.so + rm -f *.a + rm -f elf_creator + + diff --git a/utils/README.txt b/utils/README.txt new file mode 100644 index 0000000..a6c496a --- /dev/null +++ b/utils/README.txt @@ -0,0 +1,2 @@ +Some utilities that use libelf to create synthetic ELF files + diff --git a/utils/elf_creator.c b/utils/elf_creator.c new file mode 100644 index 0000000..1fd1b56 --- /dev/null +++ b/utils/elf_creator.c @@ -0,0 +1,204 @@ +/* Loosely based on the code in a Knol by Roberto Garcia Lopez: +** +** http://knol.google.com/k/roberto-garca-lpez/creating-elf-relocatable-object-files/1ohwel4gqkcn2/3# +** +** Note: This file is released under the terms of the LGPL2 license. +*/ +#include +#include +#include +#include +#include +#include +#include + + +const char* OUTFILE = "generated.o"; + +// Definition of the default string table section ".shstrtab" +const char defaultStrTable[] = +{ + /* offset 00 */ '\0', // The NULL section + /* offset 01 */ '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', '\0', + /* offset 11 */ '.', 's', 't', 'r', 't', 'a', 'b', '\0', + /* offset 19 */ '.', 's', 'y', 'm', 't', 'a', 'b', '\0', + /* offset 27 */ '.', 'c', 'o', 'm', 'm', 'e', 'n', 't', '\0', + /* offset 36 */ '.', 'b', 's', 's', '\0', + /* offset 41 */ '.', 'd', 'a', 't', 'a', '\0', + /* offset 47 */ '.', 'r', 'e', 'l', '.', 't', 'e', 'x', 't', '\0', + /* offset 57 */ '.', 't', 'e', 'x', 't', '\0' +}; + +const char defaultStrTableLen = sizeof(defaultStrTable); + +// Offsets of section names in the string table +const char _shstrtab_offset = 1; +const char _strtab_offset = 11; +const char _symtab_offset = 19; +const char _text_offset = 57; + +// Position of sections within the object file +const char _shstrtab = 1; +const char _strtab = 2; +const char _symtab = 3; +const char _text = 4; + +const char TEXT_CONTENTS[] = {0x91, 0x92, 0x93, 0x94}; + + +//---------------------------------------------------------------------------- + +int main() +{ + int FileDes; + Elf *pElf; + Elf32_Ehdr *pEhdr; + Elf32_Shdr *pShdr; + Elf_Scn *pScn; + Elf_Data *pData; + + // Create the ELF header + if (elf_version(EV_CURRENT) == EV_NONE) // It must appear before "elf_begin()" + errx(EX_SOFTWARE, "ELF library initialization failed: %s", elf_errmsg(-1)); + + if ((FileDes = open(OUTFILE, O_CREAT | O_WRONLY | O_TRUNC, 0777)) < 0) + errx(EX_OSERR, "open \"%s\" failed", "compiled.o"); + + if ((pElf = elf_begin(FileDes, ELF_C_WRITE, NULL)) == NULL) // 3rd argument is ignored for "ELF_C_WRITE" + errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); + + if ((pEhdr = elf32_newehdr(pElf)) == NULL) + errx(EX_SOFTWARE, "elf32_newehdr() failed: %s", elf_errmsg(-1)); + + pEhdr->e_ident[EI_CLASS] = ELFCLASS32; // Defined by Intel architecture + pEhdr->e_ident[EI_DATA] = ELFDATA2LSB; // Defined by Intel architecture + pEhdr->e_machine = EM_386; // Intel architecture + pEhdr->e_type = ET_REL; // Relocatable file (object file) + pEhdr->e_shstrndx = _shstrtab; // Point to the shstrtab section + + // Create the section "default section header string table (.shstrtab)" + if ((pScn = elf_newscn(pElf)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + if ((pData = elf_newdata(pScn)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + + pData->d_align = 1; + pData->d_buf = (void *) defaultStrTable; + pData->d_type = ELF_T_BYTE; + pData->d_size = defaultStrTableLen; + + if ((pShdr = elf32_getshdr(pScn)) == NULL) + errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1)); + + pShdr->sh_name = _shstrtab_offset; // Point to the name of the section + pShdr->sh_type = SHT_STRTAB; + pShdr->sh_flags = 0; + + // Create the section ".strtab" + if ((pScn = elf_newscn(pElf)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + if ((pData = elf_newdata(pScn)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + + const char strtab[] = {0, 'g', 'e', 'n', 'e', 'r', 'a', 't', 'e', 'd', '.','x', 0, '_', 's', 't', 'a', 'r', 't', 0}; + + pData->d_align = 1; + pData->d_buf = (void *) strtab; + pData->d_type = ELF_T_BYTE; + pData->d_size = sizeof(strtab); + + if ((pShdr = elf32_getshdr(pScn)) == NULL) + errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1)); + + pShdr->sh_name = _strtab_offset; + pShdr->sh_type = SHT_STRTAB; + pShdr->sh_flags = 0; + + // Create the section ".symtab" + if ((pScn = elf_newscn(pElf)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + if ((pData = elf_newdata(pScn)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + + Elf32_Sym x[4]; + + // Definition of the undefined section (this must be the first item by the definition of TIS ELF) + x[0].st_name = 0; + x[0].st_value = 0; + x[0].st_size = 0; + x[0].st_info = 0; + x[0].st_other = 0; + x[0].st_shndx = SHN_UNDEF; + + // Definition of the name of the source file (this must be the second item by the definition in TIS ELF) + x[1].st_name = 1; + x[1].st_value = 0; + x[1].st_size = 0; + x[1].st_info = ELF32_ST_INFO(STB_LOCAL, STT_FILE); // This is the value that st_info must have (because of TIS ELF) + x[1].st_other = 0; + x[1].st_shndx = SHN_ABS; // The section where the symbol is + + // Definition of the ".text" section as a section in the ".symtab" section + x[2].st_name = 0; + x[2].st_value = 0; + x[2].st_size = 0; + x[2].st_info = ELF32_ST_INFO(STB_LOCAL, STT_SECTION); + x[2].st_other = 0; + x[2].st_shndx = _text; // The section where the symbol is + + // Definition of the "_start" symbol + x[3].st_name = 13; // Offset in the "strtab" section where the name start + x[3].st_value = 0; + x[3].st_size = 0; + x[3].st_info = ELF32_ST_INFO(STB_GLOBAL, STT_NOTYPE); + x[3].st_other = 0; + x[3].st_shndx = _text; // The section where the symbol is + + pData->d_align = 4; + pData->d_buf = (void *) x; + pData->d_type = ELF_T_BYTE; + pData->d_size = sizeof(x); + + if ((pShdr = elf32_getshdr(pScn)) == NULL) + errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1)); + + pShdr->sh_name = _symtab_offset; // Point to the name of the section + pShdr->sh_type = SHT_SYMTAB; + pShdr->sh_flags = 0; + pShdr->sh_link = _strtab; // point to the section .strtab (the section that contain the strings) + pShdr->sh_info = ELF32_ST_INFO(STB_LOCAL, 3); // the second argument is beause of TIS ELF (One greater than the symbol table index of the last local symbol (binding STB_LOCAL)) + + // Create many sections named .text + for (int i = 0; i < 70000; ++i) { + if ((pScn = elf_newscn(pElf)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + if ((pData = elf_newdata(pScn)) == NULL) + errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); + + pData->d_align = 4; + pData->d_buf = (void *)TEXT_CONTENTS; + pData->d_type = ELF_T_BYTE; + pData->d_size = sizeof(TEXT_CONTENTS); + + if ((pShdr = elf32_getshdr(pScn)) == NULL) + errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1)); + + pShdr->sh_name = _text_offset; + pShdr->sh_type = SHT_PROGBITS; + pShdr->sh_flags = SHF_ALLOC | SHF_EXECINSTR; + } + + // Update the sections internally + if (elf_update(pElf, ELF_C_NULL) < 0) + errx(EX_SOFTWARE, "elf_update(NULL) failed: %s.", elf_errmsg(-1)); + // Write the object file + if (elf_update(pElf, ELF_C_WRITE) < 0) + errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); + // Close all handles + elf_end(pElf); + close(FileDes); + printf("Generated file: %s\n", OUTFILE); + + return 0; +} +