Dear all,
I tried version 0.6.1 of the elftoolchain (directly compiled from the
sourceforge repo) and the bug seems to be fixed.
But now I am facing another issue.
If the custom section is of type SHT_LOUSER, the current implementation
of elf_update() fails.
I tracked down the issue to the function _libelf_xlate_shtype() which
does not have a proper case statement for the type SHT_LOUSER. As this
function call fails, the elf_update() function aborts with an error
indicating an invalid section type.
I quick-fixed the issue in the function _libelf_xlate_shtype() by
removing the default-branch of the case statement and adding an addition
if-clause to return the correct ELF type (ELF_T_BYTE).
--------------------------------
switch (sht) {
...
case SHT_SUNW_verneed: /* == SHT_GNU_verneed */
return (ELF_T_VNEED);
case SHT_SUNW_versym: /* == SHT_GNU_versym */
return (ELF_T_HALF);
}
if (sht >= SHT_LOUSER && sht <= SHT_HIUSER) {
return (ELF_T_BYTE);
}
return -1;
--------------------------------
I guess that an additional statement may be needed for SHT_LOPROC,
SHT_HIOS or similar type which are user-defined.
Regards,
Frank Thater
Am 24.07.2014 12:25, schrieb Frank Thater:
> Dear all,
>
> I am trying to add a new section with an application specific content to
> an existing ELF file. Unfortunately the resulting ELF file is erroneous
> as the size/offset of the new section and the section type are not
> correctly set (see code snippet below).
>
> "Readelf" indicates the following information (section 37 is the newly
> added section):
>
> ...
> [36] .strtab STRTAB 00000000 013ccc 000356 00 0
> 0 1
> [37] NULL 00000000 000000 8048154 8048168
> 0 65539 0
>
> The type of the section (NULL) and the size/offset (should be 8 bytes
> starting at offset 0x14022) are wrong. I have manually verified the
> correct values within the data structures using a debugger. So I would
> guess that something gets broken during the final call to elf_update().
>
> OS is Kubuntu 12.04 with package 'libelf1" installed (Version indicated
> is 0.152-1ubuntu).
>
> I've read some old postings regarding the libelf support for ELF_C_RDWR
> which recommended to copy the sections to a new file due to a broken
> implementation. Are these bugs still present?
>
> Or am I just missing something? Any hints?
>
>
> Frank
>
>
> --------------------------------------------------------------------------------------
>
> int fd;
> Elf *elf_ref = NULL;
> Elf32_Ehdr *ehdr;
> Elf_Scn *elf_scn, *sig_scn;
> Elf_Data *elf_data;
> Elf32_Shdr *signature_scn_header;
> unsigned char sample_data[] = {0xca, 0xfe, 0xba, 0xbe, 0xca, 0xfe,
> 0xba, 0xbe};
>
> if (argc != 2) {
> return -1;
> }
>
> fd = open(argv[1], O_RDWR);
>
> /* Protect from using a lower ELF version and initialize ELF library */
> if (elf_version(EV_CURRENT) == EV_NONE) {
> printf("ELF library init failed: %s\n", elf_errmsg(-1));
> close(fd);
> return -1;
> }
>
> elf_ref = elf_begin(fd, ELF_C_RDWR, NULL);
>
> if (elf_kind(elf_ref) != ELF_K_ELF) {
> printf("Program is not an ELF binary\n");
> close(fd);
> return -2;
> }
>
> sig_scn = elf_newscn(elf_ref);
>
> elf_data = elf_newdata(sig_scn);
> elf_data->d_align = 1;
> elf_data->d_off = 0LL ;
> elf_data->d_buf = sample_data ;
> elf_data->d_type = ELF_T_BYTE ;
> elf_data->d_size = sizeof(sample_data);
> elf_data->d_version = EV_CURRENT ;
>
> signature_scn_header = elf32_getshdr(sig_scn);
> signature_scn_header->sh_name = 0;
> signature_scn_header->sh_type = SHT_LOUSER + 10;
>
> if (elf_update(elf_ref , ELF_C_NULL ) < 0) {
> printf("ELF update failed: %s", elf_errmsg (-1));
> return -3;
> }
>
> (void) elf_flagshdr(sig_scn, ELF_C_SET, ELF_F_DIRTY);
> (void) elf_flagscn(sig_scn, ELF_C_SET, ELF_F_DIRTY);
> (void) elf_flagdata(elf_data, ELF_C_SET, ELF_F_DIRTY);
> (void) elf_flagehdr(elf_ref, ELF_C_SET, ELF_F_DIRTY);
> (void) elf_flagelf(elf_ref, ELF_C_SET, ELF_F_DIRTY);
>
> if (elf_update(elf_ref , ELF_C_WRITE ) < 0) {
> printf("ELF update failed: %s", elf_errmsg (-1));
> return -4;
> }
>
> elf_end(elf_ref);
>
> close(fd);
>
------------------------------------------------------------------------------
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