fix: image size computation on Apple

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 **Fixes**:
 
+- Native/macOS: fix module `image_size` computation, which could have caused the symbolicator to misattribute every frame to the lowest-addressed image (typically `dyld` or `libsystem`). ([#1740](https://github.com/getsentry/sentry-native/pull/1740))
 - Native: raise `SENTRY_CRASH_MAX_MODULES` from `512` to `2048` so processes that load many shared libraries no longer have their minidump module list truncated, which left frames in unrecorded modules without a `debug_id` and unsymbolicatable.
   ([#1738](https://github.com/getsentry/sentry-native/pull/1738))
 - Reject overly deep msgpack payloads during deserialization. ([#1727](https://github.com/getsentry/sentry-native/pull/1727))

src/backends/native/sentry_crash_handler.c

@@ -562,31 +562,30 @@ crash_signal_handler(int signum, siginfo_t *info, void *context)
             const struct mach_header_64 *header64
                 = (const struct mach_header_64 *)header;
             const uint8_t *cmds = (const uint8_t *)(header64 + 1);
+            bool has_size = false;
+            bool has_uuid = false;
 
-            for (uint32_t j = 0; j < header64->ncmds && j < 256; j++) {
+            for (uint32_t j = 0;
+                j < header64->ncmds && j < 256 && (!has_size || !has_uuid);
+                j++) {
                 const struct load_command *cmd
                     = (const struct load_command *)cmds;
 
                 if (cmd->cmd == LC_SEGMENT_64) {
                     const struct segment_command_64 *seg
                         = (const struct segment_command_64 *)cmd;
-                    // Skip __PAGEZERO which has vmsize=4GB on 64-bit and
-                    // would vastly inflate the module size
-                    if (seg->initprot == 0 && seg->maxprot == 0) {
-                        cmds += cmd->cmdsize;
-                        if (cmd->cmdsize == 0)
-                            break;
-                        continue;
-                    }
-                    uint64_t seg_end = seg->vmaddr + seg->vmsize;
-                    if (seg_end > size) {
-                        size = seg_end;
+                    // image_size on macOS is the __TEXT segment's vmsize:
+                    // https://github.com/getsentry/sentry-native/blob/82dec4b8518de32586c4a761a3a9df4aed9d7b8d/src/modulefinder/sentry_modulefinder_apple.c#L65-L69
+                    if (memcmp(seg->segname, "__TEXT", 7) == 0) {
+                        size = seg->vmsize;
+                        has_size = true;
                     }
                 } else if (cmd->cmd == LC_UUID) {
                     // Extract UUID for symbolication
                     const struct uuid_command *uuid_cmd
                         = (const struct uuid_command *)cmd;
                     signal_safe_memcpy(module->uuid, uuid_cmd->uuid, 16);
+                    has_uuid = true;
                 }
 
                 cmds += cmd->cmdsize;

tests/assertions.py

@@ -182,6 +182,29 @@ def assert_event_meta(
         )
 
 
+def assert_debug_meta_images_do_not_overlap(event):
+    """Validate ``event["debug_meta"]["images"]`` shape.
+
+    The half-open ranges ``[image_addr, image_addr + image_size)`` must not
+    overlap -- the symbolicator relies on this to attribute frames to images.
+    """
+    images = event["debug_meta"]["images"]
+    assert len(images) > 0, "debug_meta should contain at least one image"
+
+    ranges = []
+    for image in images:
+        name = image.get("code_file") or image.get("debug_file") or "<unknown>"
+        addr = int(image["image_addr"], 16)
+        ranges.append((addr, addr + image["image_size"], name))
+
+    ranges.sort()
+    for (a_start, a_end, a_name), (b_start, b_end, b_name) in zip(ranges, ranges[1:]):
+        assert a_end <= b_start, (
+            f"image ranges overlap: {a_name} [{a_start:#x}, {a_end:#x}) "
+            f"vs {b_name} [{b_start:#x}, {b_end:#x})"
+        )
+
+
 def is_valid_hex(s):
     if not s.lower().startswith("0x"):
         return False

tests/test_integration_native.py

@@ -20,6 +20,7 @@
 )
 from .assertions import (
     assert_breadcrumb,
+    assert_debug_meta_images_do_not_overlap,
     assert_meta,
     assert_native_crash,
     assert_session,
@@ -903,6 +904,8 @@ def test_crash_mode_native_only(cmake, httpserver):
     # Should have debug_meta
     assert "debug_meta" in event
     assert len(event["debug_meta"]["images"]) > 0
+    if sys.platform == "darwin":
+        assert_debug_meta_images_do_not_overlap(event)
 
 
 def test_crash_mode_native_with_minidump(cmake, httpserver):
@@ -947,6 +950,8 @@ def test_crash_mode_native_with_minidump(cmake, httpserver):
 
     # Should have debug_meta
     assert "debug_meta" in event
+    if sys.platform == "darwin":
+        assert_debug_meta_images_do_not_overlap(event)
 
 
 def test_native_cache_consent(cmake, httpserver):