allow loading images from offsets

gc_heap.c

@@ -574,21 +574,27 @@ char* sexp_load_image_err() {
   return gc_heap_err_str;
 }
 
-sexp sexp_load_image (const char* filename, sexp_uint_t heap_free_size, sexp_uint_t heap_max_size) {
+sexp sexp_load_image (const char* filename, off_t offset, sexp_uint_t heap_free_size, sexp_uint_t heap_max_size) {
-  sexp res = NULL;
+  struct load_image_state state;
-  sexp ctx = NULL;
+  struct sexp_image_header_t header;
+  FILE *fp;
+  int i;
+  sexp res = NULL, ctx = NULL, base, *ctx_globals, *ctx_types;
+
   gc_heap_err_str[0] = 0;
 
-  struct load_image_state state;
   memset(&state, 0, sizeof(struct load_image_state));
 
-  FILE *fp = fopen(filename, "rb");
+  fp = fopen(filename, "rb");
   if (!fp) {
     snprintf(gc_heap_err_str, ERR_STR_SIZE, "couldn't open image file for reading: %s\n", filename);
     goto done;
   }
+  if (offset > 0 && fseek(fp, offset, SEEK_SET) < 0) {
+    snprintf(gc_heap_err_str, ERR_STR_SIZE, "couldn't seek to image offset: %s -> %lld: %s\n", filename, offset, strerror(errno));
+    goto done;
+  }
 
-  struct sexp_image_header_t header;
   if (!load_image_header(fp, &header)) { goto done; }
 
   state.heap = sexp_gc_packed_heap_make(header.size, heap_free_size);
@@ -596,7 +602,7 @@ sexp sexp_load_image (const char* filename, sexp_uint_t heap_free_size, sexp_uin
     snprintf(gc_heap_err_str, ERR_STR_SIZE, "couldn't malloc heap\n");
     goto done;
   }
-  sexp base = sexp_heap_first_block(state.heap);
+  base = sexp_heap_first_block(state.heap);
 
   if (fread(base, 1, header.size, fp) != header.size) {
     snprintf(gc_heap_err_str, ERR_STR_SIZE, "error reading image\n");
@@ -614,24 +620,23 @@ sexp sexp_load_image (const char* filename, sexp_uint_t heap_free_size, sexp_uin
      copy of the type array pointers with correct offsets is applied is created outside
      of the new heap to be used with the pointer adjustment process.
   */
-  sexp* ctx_globals = sexp_vector_data((sexp)((unsigned char*)sexp_context_globals(ctx) + state.offset));
+  ctx_globals = sexp_vector_data((sexp)((unsigned char*)sexp_context_globals(ctx) + state.offset));
-  sexp* ctx_types   = sexp_vector_data((sexp)((unsigned char*)(ctx_globals[SEXP_G_TYPES]) + state.offset));
+  ctx_types   = sexp_vector_data((sexp)((unsigned char*)(ctx_globals[SEXP_G_TYPES]) + state.offset));
   state.types_cnt   = sexp_unbox_fixnum(ctx_globals[SEXP_G_NUM_TYPES]);
   state.types = malloc(sizeof(sexp) * state.types_cnt);
   if (!state.types) goto done;
-  int i;
   for (i = 0; i < state.types_cnt; i++) {
     state.types[i] = (sexp)((unsigned char *)ctx_types[i] + state.offset);
   }
 
   if (sexp_gc_heap_walk(ctx, sexp_context_heap(ctx), state.types, state.types_cnt,
-                        &state, NULL, NULL, load_image_callback_p1) != SEXP_TRUE) {
+                        &state, NULL, NULL, load_image_callback_p1) != SEXP_TRUE)
-    goto done; }
+    goto done;
 
   /* Second pass to fix code references */
   if (sexp_gc_heap_walk(ctx, sexp_context_heap(ctx), state.types, state.types_cnt,
-                        &state, NULL, NULL, load_image_callback_p2) != SEXP_TRUE) {
+                        &state, NULL, NULL, load_image_callback_p2) != SEXP_TRUE)
-    goto done; }
+    goto done;
 
   if (heap_max_size > SEXP_INITIAL_HEAP_SIZE) {
     sexp_context_heap(ctx)->max_size = heap_max_size;

include/chibi/gc_heap.h

@@ -82,7 +82,7 @@ SEXP_API sexp sexp_save_image (sexp ctx, const char* filename);
    to provide a description of the error encountered.  An sexp exception cannot be
    returned because there is not a valid context in which to put the exception.
 */
-SEXP_API sexp sexp_load_image (const char* filename, sexp_uint_t heap_free_size, sexp_uint_t heap_max_size);
+SEXP_API sexp sexp_load_image (const char* filename, off_t offset, sexp_uint_t heap_free_size, sexp_uint_t heap_max_size);
 
 
 /* In the case that sexp_load_image() returns NULL, this function will return

main.c

@@ -409,7 +409,7 @@ sexp run_main (int argc, char **argv) {
         fprintf(stderr, "-:i <file>: image files must be loaded first\n");
         exit_failure();
       }
-      ctx = sexp_load_image(arg, heap_size, heap_max_size);
+      ctx = sexp_load_image(arg, 0, heap_size, heap_max_size);
       if (!ctx || !sexp_contextp(ctx)) {
         fprintf(stderr, "-:i <file>: couldn't open file for reading: %s\n", arg);
         fprintf(stderr, "            %s\n", sexp_load_image_err());