Fixes

Author: mujacica

src/backends/native/minidump/sentry_minidump_format.h

@@ -476,16 +476,19 @@ PACKED_STRUCT_END
 /**
  * Linux DSO debug structures (MD_LINUX_DSO_DEBUG, 0x4767000A)
  *
- * Mirrors Breakpad's MDRawLinkMap64 / MDRawDebug64. LLDB and rust-minidump
- * use this stream to enumerate loaded shared objects when LinuxAuxv alone
- * isn't enough (e.g. modules loaded via dlopen after process startup that
- * aren't in /proc/<pid>/maps in a usable order).
+ * Wire-compatible with Breakpad's MDRawLinkMap64 / MDRawDebug64. Breakpad
+ * builds these under `#pragma pack(push, 4)`, so a uint64_t can sit on a
+ * 4-byte boundary with no padding inserted between the preceding uint32_t
+ * and itself. We use PACKED_ATTR (== __attribute__((packed))) to get the
+ * same byte-exact layout: 20 bytes for link_map64, 36 bytes for debug64.
+ *
+ * Adding explicit _pad fields here would break the layout — LLDB and
+ * rust-minidump compute offsets assuming the Breakpad sizes.
  */
 PACKED_STRUCT_BEGIN
 typedef struct {
     uint64_t addr; // l_addr from struct link_map
     minidump_rva_t name; // RVA to MINIDUMP_STRING with the SO path
-    uint32_t _pad;
     uint64_t ld; // l_ld from struct link_map (PT_DYNAMIC of this DSO)
 } PACKED_ATTR minidump_link_map64_t;
 PACKED_STRUCT_END
@@ -495,7 +498,6 @@ typedef struct {
     uint32_t version; // r_debug.r_version
     minidump_rva_t map; // RVA to array of minidump_link_map64_t
     uint32_t dso_count; // number of entries in map
-    uint32_t _pad;
     uint64_t brk; // r_debug.r_brk
     uint64_t ldbase; // r_debug.r_ldbase
     uint64_t dynamic; // address of the program's _DYNAMIC section

src/backends/native/minidump/sentry_minidump_linux.c

@@ -2874,8 +2874,10 @@ sentry__write_minidump(
     minidump_writer_t writer = { 0 };
     writer.crash_ctx = ctx;
 
-    // Open output file
-    writer.fd = open(output_path, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    // Open output file. O_RDWR (not O_WRONLY) because SMART-mode indirect
+    // memory capture pread()'s thread-stack bytes back from the dump after
+    // they're written, so it can scan them for heap pointers.
+    writer.fd = open(output_path, O_RDWR | O_CREAT | O_TRUNC, 0600);
     if (writer.fd < 0) {
         SENTRY_WARNF("failed to create minidump: %s", strerror(errno));
         return -1;

src/backends/native/minidump/sentry_minidump_macos.c

@@ -1378,9 +1378,11 @@ sentry__write_minidump(
     minidump_writer_t writer = { 0 };
     writer.crash_ctx = ctx;
 
-    // Open output file
+    // Open output file. O_RDWR (not O_WRONLY) because SMART-mode indirect
+    // memory capture pread()'s thread-stack bytes back from the dump after
+    // they're written, so it can scan them for heap pointers.
     SENTRY_DEBUGF("write_minidump: opening file %s", output_path);
-    writer.fd = open(output_path, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    writer.fd = open(output_path, O_RDWR | O_CREAT | O_TRUNC, 0600);
     if (writer.fd < 0) {
         SENTRY_WARN("write_minidump: failed to open file");
         return -1;