https://github.com/no-defun-allowed/ccl/blob/master/lisp-kernel/gdb.c GDB plugin thingy

ccl-symbols.c

#include <gdb/jit-reader.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

GDB_DECLARE_GPL_COMPATIBLE_READER;

static enum gdb_status read_debug_info(struct gdb_reader_funcs *self, struct gdb_symbol_callbacks *cbs, void *memory, long bytes) {
  fprintf(stderr, "time to read %ld bytes\n", bytes);
  char *mem = (char*)memory, *mem_end = (char*)memory + bytes;
  struct gdb_object *object = cbs->object_open(cbs);
  struct gdb_symtab *symtab = cbs->symtab_open(cbs, object, "ccl");

  int count = 0;
  GDB_CORE_ADDR bottom = -1, top = 0;
  
  while (mem < mem_end) {
    char name[128];
    GDB_CORE_ADDR begin, end;
    begin = *(GDB_CORE_ADDR*)mem; mem += sizeof(GDB_CORE_ADDR);
    if (end > top) top = end;
    if (begin < bottom) bottom = begin;
    end = *(GDB_CORE_ADDR*)mem; mem += sizeof(GDB_CORE_ADDR);
    strncpy(name, mem, 128);
    /* Skip over the string */
    mem += strlen(mem) + 1;
    cbs->block_open(cbs, symtab, NULL, begin, end, name);
    count++;
  }

  cbs->symtab_close(cbs, symtab);
  cbs->object_close(cbs, object);
  if (mem > mem_end) {
    fprintf(stderr, "fell off end, %ld bytes of %ld\n", mem - (char*)memory, bytes);
    return GDB_FAIL;
  } else {
    fprintf(stderr, "read %d Lisp symbols in %lx...%lx\n", count, bottom, top);
    return GDB_SUCCESS;
  }
}

static GDB_CORE_ADDR read_register(struct gdb_unwind_callbacks *cbs, int n) {
  struct gdb_reg_value *value = cbs->reg_get(cbs, n);
  GDB_CORE_ADDR reg;
  memcpy(&reg, value->value, 8);
  value->free(value);
  return reg;
}
static void write_register(struct gdb_unwind_callbacks *cbs, int n, GDB_CORE_ADDR v) {
  /* gdb_reg_value has room for one byte of value[], we want a word */
  struct gdb_reg_value *value = malloc(sizeof(struct gdb_reg_value) + sizeof(GDB_CORE_ADDR) - 1);
  value->defined = 1;
  value->free = free;
  memcpy(&value->value, &v, 8);
  cbs->reg_set(cbs, n, value);
}
static GDB_CORE_ADDR read_word(struct gdb_unwind_callbacks *cbs, GDB_CORE_ADDR addr) {
  GDB_CORE_ADDR word;
  cbs->target_read(addr, &word, sizeof(GDB_CORE_ADDR));
  return word;
}

#define RIP 16
#define RBP 6

static enum gdb_status unwind_frame(struct gdb_reader_funcs* self, struct gdb_unwind_callbacks* cbs) {
  GDB_CORE_ADDR bp = read_register(cbs, RBP);
  GDB_CORE_ADDR old_bp = read_word(cbs, bp), old_rip = read_word(cbs, bp + 8);
  write_register(cbs, RBP, old_bp);
  write_register(cbs, RIP, old_rip);
  return GDB_SUCCESS;
}

static struct gdb_frame_id get_frame_id(struct gdb_reader_funcs* self, struct gdb_unwind_callbacks* cbs) {
  GDB_CORE_ADDR pc = read_register(cbs, RIP), sp = read_register(cbs, RBP);
  struct gdb_frame_id frame = {pc, sp};
  return frame;
}

static void destroy_reader(struct gdb_reader_funcs* self) { }

static struct gdb_reader_funcs reader = {GDB_READER_INTERFACE_VERSION, NULL, read_debug_info, unwind_frame, get_frame_id, destroy_reader};

struct gdb_reader_funcs* gdb_init_reader(void) { return &reader; }