use libelf to find code offset in the exe

riscv64.c

@@ -0,0 +1,74 @@
+#include <gelf.h>
+#include <libelf.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+  size_t offset;
+  size_t size;
+} Section;
+
+Section get_code_section(uint8_t *exe_bytes, size_t exe_size) {
+  Elf *elf = elf_memory((char *)exe_bytes, exe_size);
+  if (!elf) {
+    fprintf(stderr, "elf_begin failed: %s\n", elf_errmsg(-1));
+    exit(1);
+  }
+
+  size_t str_table_index;
+  if (elf_getshdrstrndx(elf, &str_table_index) != 0) {
+    fprintf(stderr, "elf_getshdrstrndx failed: %s\n", elf_errmsg(-1));
+    exit(1);
+  }
+
+  Elf_Scn *section = NULL;
+  while ((section = elf_nextscn(elf, section)) != NULL) {
+    GElf_Shdr header;
+    if (gelf_getshdr(section, &header) != &header)
+      continue;
+
+    const char *name = elf_strptr(elf, str_table_index, header.sh_name);
+    if (name && strcmp(name, ".text") == 0) {
+      elf_end(elf);
+      return (Section){.offset = header.sh_offset, .size = header.sh_size};
+    }
+  }
+
+  fprintf(stderr, "Failed to locate .text\n");
+  exit(1);
+}
+
+int main(int argc, char *argv[]) {
+  if (elf_version(EV_CURRENT) == EV_NONE) {
+    fprintf(stderr, "Failed to initialize libelf: %s\n", elf_errmsg(-1));
+    return 1;
+  }
+
+  const char *path = NULL;
+  for (int i = 1; i < argc; i++) {
+    path = argv[i];
+  }
+
+  if (path == NULL) {
+    fprintf(stderr, "Usage: %s <path>\n", argv[0]);
+    return 1;
+  }
+
+  FILE *file = fopen(path, "rb");
+  if (!file) {
+    fprintf(stderr, "Failed to open %s\n", path);
+    return 1;
+  }
+
+  // probably enough for anything we can handle
+  uint8_t *exe_bytes = malloc(20 * 1024 * 1024);
+  size_t exe_size = fread(exe_bytes, 1, 20 * 1024 * 1024, file);
+  fclose(file);
+
+  Section section = get_code_section(exe_bytes, exe_size);
+
+  printf("Offset: %zu\n", section.offset);
+  printf("Size: %zu\n", section.size);
+}