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Introduction to elf parsing

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This commit is contained in:
Bahadir Balban
2008-11-20 17:34:12 +02:00
parent 1914e58be9
commit 27d331895b
2 changed files with 36 additions and 11 deletions
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3
tasks/mm0/src/execve.c
View File

@@ -78,7 +78,8 @@ int task_setup_from_executable(struct vm_file *vmfile, struct tcb *task,
{ {
memset(efd, 0, sizeof(*efd)); memset(efd, 0, sizeof(*efd));
return 0; return elf_parse_executable(task, vmfile, efd,
pager_map_page, pager_unmap_page);
} }
int do_execve(struct tcb *sender, char *filename) int do_execve(struct tcb *sender, char *filename)

44
tasks/mm0/src/lib/elf/elf.c
View File

@@ -14,9 +14,9 @@ int elf_probe(struct elf_header *header)
{ {
/* Test that it is a 32-bit little-endian ELF file */ /* Test that it is a 32-bit little-endian ELF file */
if (header->e_ident[EI_MAG0] == ELFMAG0 && if (header->e_ident[EI_MAG0] == ELFMAG0 &&
header->e_ident[EI_MAG1] == ELFMAG1 && header->e_ident[EI_MAG1] == ELFMAG1 &&
header->e_ident[EI_MAG2] == ELFMAG2 && header->e_ident[EI_MAG2] == ELFMAG2 &&
header->e_ident[EI_MAG3] == ELFMAG3 && header->e_ident[EI_MAG3] == ELFMAG3 &&
header->e_ident[EI_CLASS] == ELFCLASS32 && header->e_ident[EI_CLASS] == ELFCLASS32 &&
header->e_ident[EI_DATA] == ELFDATA2LSB) header->e_ident[EI_DATA] == ELFDATA2LSB)
return 0; return 0;
@@ -24,19 +24,43 @@ int elf_probe(struct elf_header *header)
return -1; return -1;
} }
/*
int elf_parse_executable(struct vm_file *f) * Loading an ELF file:
*
* This first probes and detects that the given file is a valid elf file.
* Then it looks at the program header table to find the first (probably
* only) segment that has type LOAD. Then it looks at the section header
* table, to find out about every loadable section that is part of this
* aforementioned loadable program segment. Each section is marked in the
* efd and tcb structures for further memory mappings. Loading an elf
* executable is simple as that, but it is described poorly in manuals.
*/
int elf_parse_executable(struct tcb *task, struct vm_file *file,
struct exec_file_desc *efd)
{ {
int err; int err;
struct elf_header *elf_header = pager_map_page(f, 0); struct elf_header *elf_header = pager_map_page(file, 0);
struct elf_program_header *prg_header; struct elf_program_header *prg_header_start, *prg_header_load;
struct elf_section_header *sect_header; struct elf_section_header *sect_header_start;
/* Test that it is a valid elf file */ /* Test that it is a valid elf file */
if ((err = elf_probe(elf_header)) < 0) if ((err = elf_probe(elf_header)) < 0)
return err; return err;
/* Get the program header table */ /* Get the program header table */
prg_header = (struct elf_program_header *)((void *)elf_header + elf_header->e_phoff); prg_header_start = (struct elf_program_header *)
((void *)elf_header + elf_header->e_phoff);
/* Get the first loadable segment */
for (int i = 0; i < elf_header->e_phnum; i++) {
if (prg_header_start[i].type == PT_LOAD) {
prg_header_load = &prg_header_start[i];
break;
}
}
/* Get the section header table */
sect_header_start = (struct elf_section_header *)
((void *)elf_header + elf_header->e_shoff);
} }