Get custom note out of core file

note.c

#include <dwarf.h>
#include <elfutils/libdwelf.h>
#include <elfutils/libdwfl.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <inttypes.h>
#include <string.h>

static int module_callback (Dwfl_Module *mod, void **userdata, const char *name, Dwarf_Addr start, void *arg)
{
        const unsigned char *id;
        GElf_Addr id_vaddr;
        int id_len;

        assert(mod);

        GElf_Addr bias;
        Elf *elf = dwfl_module_getelf(mod, &bias);
        if (!elf) {
                printf("elf_begin() failed: %s\n", elf_errmsg(-1));
                return DWARF_CB_ABORT;
        }

        size_t n_program_headers;
        int r = elf_getphdrnum(elf, &n_program_headers);
        if (r < 0) {
                printf("Could not parse number of program headers in core file: %s\n", elf_errmsg(-1));
                elf_end(elf);
                return DWARF_CB_ABORT;
        }
        for (size_t i = 0; i < n_program_headers; ++i) {
                GElf_Phdr mem;
                GElf_Phdr *header = gelf_getphdr (elf, i, &mem);

                if (header == NULL || header->p_type != PT_NOTE)
                        continue;

                Elf_Data *data = elf_getdata_rawchunk(elf,
                                                      header->p_offset,
                                                      header->p_filesz,
                                                      header->p_align == 8 ? ELF_T_NHDR8 : ELF_T_NHDR);
                GElf_Nhdr note_header;
                size_t offset = 0;
                size_t name_offset, desc_offset;
                while (offset < data->d_size && (offset = gelf_getnote(data, offset, &note_header, &name_offset, &desc_offset)) > 0) {
                        const char *nname = note_header.n_namesz == 0 ? "" : (const char *)data->d_buf + name_offset;
                        const char *desc = (const char *)data->d_buf + desc_offset;

                        if (note_header.n_namesz == 0)
                            continue;
                        if (memcmp(nname, "TBD", 3) == 0)
                                printf("Fount TBD note with payload: %s\n", desc);
                }
        }

        return DWARF_CB_OK;
}

int main(int argc, char **argv) {

        static const Dwfl_Callbacks callbacks = {
                .find_elf = dwfl_build_id_find_elf,
                .section_address = dwfl_offline_section_address,
                .find_debuginfo = dwfl_standard_find_debuginfo,
        };

        Dwfl *dwfl = NULL;
        Elf *elf = NULL;
        int r;
        int fd;

        assert(argc > 1);

        fd = open(argv[1], O_CLOEXEC|O_RDONLY);
        if (fd < 0)
                return -1;

        elf_version(EV_CURRENT);

        elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
        if (!elf) {
                r = -EINVAL;
                goto finish;
        }

        dwfl = dwfl_begin(&callbacks);
        if (!dwfl) {
                r = -EINVAL;
                goto finish;
        }

        if (dwfl_core_file_report(dwfl, elf, NULL) < 0) {
                r = -EINVAL;
                goto finish;
        }

        if (dwfl_report_end(dwfl, NULL, NULL) != 0) {
                r = -EINVAL;
                goto finish;
        }

        if (dwfl_getmodules(dwfl, &module_callback, NULL, 0) < 0) {
                r = -EINVAL;
                goto finish;
        }

        r = 0;

finish:
        if (dwfl)
                dwfl_end(dwfl);

        if (elf)
                elf_end(elf);

        close(fd);

        return r;
}