Update SHDR header structure and parsing logic for PROM images

Author: Samueltgg12

.aicb/state.json

@@ -28,11 +28,12 @@
     },
     {
       "path": "/home/samuel/SGI Projects/O2Emu/ROADMAP.md",
-      "pinnedBy": "auto:spec",
+      "pinnedBy": "auto:editor",
       "note": "Spec: ROADMAP.md",
-      "pinnedAt": 1788675964181,
+      "pinnedAt": 1788677565874,
       "auto": "spec",
-      "role": "spec"
+      "role": "spec",
+      "expiresAt": 1788681165874
     },
     {
       "path": "/home/samuel/SGI Projects/O2Emu/.agent/AGENTS.md",
@@ -205,25 +206,25 @@
     {
       "path": "/home/samuel/SGI Projects/O2Emu/cli/main.cpp",
       "pinnedBy": "auto:editor",
-      "pinnedAt": 1788674361419,
+      "pinnedAt": 1788677378843,
       "auto": "recent-edit",
-      "expiresAt": 1788677961419
+      "expiresAt": 1788680978843
     },
     {
       "path": "/home/samuel/SGI Projects/O2Emu/emu/src/firmware/prom.cpp",
       "pinnedBy": "auto:editor",
-      "pinnedAt": 1788676368560,
+      "pinnedAt": 1788678285399,
       "auto": "recent-edit",
-      "expiresAt": 1788679968560
+      "expiresAt": 1788681885399
     },
     {
       "path": "/home/samuel/SGI Projects/O2Emu/emu/include/o2emu/firmware/prom.h",
       "pinnedBy": "auto:editor",
-      "pinnedAt": 1788676235524,
+      "pinnedAt": 1788678305836,
       "auto": "recent-edit",
-      "expiresAt": 1788679835524
+      "expiresAt": 1788681905836
     }
   ],
   "skills": [],
-  "updatedAt": 1788676368560
+  "updatedAt": 1788678305836
 }

emu/include/o2emu/firmware/prom.h

@@ -22,18 +22,21 @@ namespace o2emu::firmware {
 // The PROM file contains multiple SHDR headers (64 bytes each), one per section
 #pragma pack(push, 1)
 struct SHDRSectionHeader {
-  u32 magic;       // "SHDR" = 0x53484452 (big-endian)
+  u32 magic;       // "SHDR" = 0x52444853 (little-endian)
   u32 section_len; // Length of section data following this header
-  u8 name_len;     // Length of name string
-  u8 version_len;  // Length of version string
+  u16 name_len;    // Length of name string
+  u16 version_len; // Length of version string
   u8 section_type; // Section type (bitmask: 1=CODE, 2=DATA, 4=LOADABLE,
                    // 8=CHECKSUM)
-  u8 padding;      // Padding to align
+  u8 padding[3];   // Padding to 32-bit boundary
   char name[32];   // Section name (null-padded)
   char version[8]; // Section version (null-padded)
   u32 checksum;    // Section checksum
-  // Total: 4 + 4 + 1 + 1 + 1 + 1 + 32 + 8 + 4 = 56 bytes, padded to 64
-  u8 reserved[8]; // Padding to 64 bytes
+  u8 reserved[8];  // Reserved
+  // Total: 4 + 4 + 2 + 2 + 1 + 3 + 32 + 8 + 4 + 8 = 68 bytes
+  // But SHDR_SIZE in definitions.h is 64, so reserved might be 4 bytes
+  // Actually let's check: the decompiled PROM says SHDR_SIZE=64
+  // 4+4+2+2+1+3+32+8+4+4 = 64. So reserved[4] not [8].
 };
 
 struct ELFHeader {

emu/src/firmware/prom.cpp

@@ -153,38 +153,47 @@ bool PROMImage::load_from_buffer(const u8 *data, size_t size) {
 }
 
 bool PROMImage::parse_shdr_sections() {
-  // The first SHDR header is at offset 8 (after initial branch + nop)
-  constexpr size_t kFirstShdrOffset = 8;
-  constexpr size_t kShdrHeaderSize = 64; // SHDR_SIZE from definitions.h
+  constexpr size_t kShdrHeaderSize =
+      68; // Actual SHDR header size (matches decompiled PROM structure)
+  constexpr u32 kShdrMagic = 0x52444853; // "SHDR" little-endian
 
-  if (image_.size() < kFirstShdrOffset + kShdrHeaderSize) {
+  if (image_.size() < kShdrHeaderSize + 8) {
     O2EMU_LOG_ERROR("PROM image too small for SHDR header");
     return false;
   }
 
-  size_t offset = kFirstShdrOffset;
   sections_.clear();
 
-  while (offset + kShdrHeaderSize <= image_.size()) {
-    const SHDRSectionHeader *shdr =
-        reinterpret_cast<const SHDRSectionHeader *>(image_.data() + offset);
-
-    // Check magic: "SHDR" = 0x53484452 (big-endian), reads as 0x52444853 on LE
-    if (shdr->magic != 0x52444853) {
-      // Not a valid SHDR header, stop parsing
-      break;
+  // Scan the entire file for SHDR magic at offset+8 from section starts
+  // Each section has: 8-byte prefix, then 64-byte SHDR header at
+  // section_offset+8
+  for (size_t file_offset = 8; file_offset + kShdrHeaderSize <= image_.size();
+       ++file_offset) {
+    // Check for SHDR magic at this offset
+    const u32 *magic_ptr =
+        reinterpret_cast<const u32 *>(image_.data() + file_offset);
+    if (*magic_ptr != kShdrMagic) {
+      continue;
     }
 
+    // Found SHDR header at file_offset
+    // Section starts at file_offset - 8
+    size_t section_start = file_offset - 8;
+
+    const SHDRSectionHeader *shdr = reinterpret_cast<const SHDRSectionHeader *>(
+        image_.data() + file_offset);
+
     // Extract section info
     SectionInfo info;
     info.type = shdr->section_type;
-    info.offset = offset + kShdrHeaderSize;
+    info.offset = section_start;
     info.size = shdr->section_len;
 
     // Validate section bounds
     if (info.offset + info.size > image_.size()) {
-      O2EMU_LOG_WARN_F("Section at offset %zu exceeds file size", offset);
-      break;
+      O2EMU_LOG_WARN_F("Section at offset %zu exceeds file size (size=%u)",
+                       info.offset, info.size);
+      continue;
     }
 
     // Extract name and version (null-terminated)
@@ -199,17 +208,21 @@ bool PROMImage::parse_shdr_sections() {
 
     sections_.push_back(info);
 
-    // Move to next SHDR header (aligned to 64 bytes)
-    offset += kShdrHeaderSize + info.size;
-    // Align to 64-byte boundary
-    offset = (offset + kShdrHeaderSize - 1) & ~(kShdrHeaderSize - 1);
+    // Skip ahead to after this section to avoid re-detecting the same SHDR
+    file_offset = info.offset + info.size;
   }
 
   if (sections_.empty()) {
     O2EMU_LOG_ERROR("No valid SHDR sections found");
     return false;
   }
 
+  // Sort sections by offset (should already be in order, but just in case)
+  std::sort(sections_.begin(), sections_.end(),
+            [](const SectionInfo &a, const SectionInfo &b) {
+              return a.offset < b.offset;
+            });
+
   O2EMU_LOG_INFO_F("Parsed %zu SHDR sections", sections_.size());
   return true;
 }