Rev Struct

rev-struct - Structure Recovery

Recover data structure definitions by analyzing memory access patterns in functions and their call chains.

Pre-check

Determine which IDA access method is available:

Option A — IDA Pro MCP (preferred if connected): Check if the IDA Pro MCP server is connected (look for an active ida-pro or equivalent MCP connection). If connected, you can query IDA directly via MCP tools — no exported files needed. Proceed with the analysis using MCP.

Option B — IDA-NO-MCP exported data: If MCP is not connected, check if IDA-NO-MCP exported data exists in the current directory:

1. Check if decompile/ directory exists
2. Check if there are .c files inside

If neither MCP nor exported data is available, prompt the user:

No IDA access method detected. Choose one of the following:
Option A — IDA Pro MCP (recommended):  Connect the IDA Pro MCP server so Claude can query IDA directly.
Option B — IDA-NO-MCP export:  1. Download plugin: https://github.com/P4nda0s/IDA-NO-MCP  2. Copy INP.py to IDA plugins directory  3. Press Ctrl-Shift-E in IDA to export  4. Open the exported directory with Claude Code

Export Directory Structure

./├── decompile/              # Decompiled C code directory│   ├── 0x401000.c          # One file per function, named by hex address│   ├── 0x401234.c│   └── ...├── decompile_failed.txt    # Failed decompilation list├── decompile_skipped.txt   # Skipped functions list├── strings.txt             # String table (address, length, type, content)├── imports.txt             # Import table (address:function_name)├── exports.txt             # Export table (address:function_name)└── memory/                 # Memory hexdump (1MB chunks)

Function File Format (decompile/*.c)

Each .c file contains function metadata comments and decompiled code:

/* * func-name: sub_401000 * func-address: 0x401000 * callers: 0x402000, 0x403000    // List of functions that call this function * callees: 0x404000, 0x405000    // List of functions called by this function */
int __fastcall sub_401000(int a1, int a2){    // Decompiled code...}

Structure Recovery Steps

Step 1: Read Target Function

1. Based on the user-provided address, read decompile/<address>.c
2. Parse function metadata, extract callers and callees lists
3. Identify pointer parameters in the function (potential structure pointers)

Step 2: Collect Memory Access Patterns

Search for the following patterns in the target function:

Direct offset access:

*(a1 + 0x10)           // offset 0x10*(_DWORD *)(a1 + 8)    // offset 0x8, DWORD type*(_QWORD *)(a1 + 0x20) // offset 0x20, QWORD type*(_BYTE *)(a1 + 4)     // offset 0x4, BYTE type

Array access:

*(a1 + 8 * i)          // array, element size 8 bytesa1[i]                  // array access

Nested structures:

*(*a1 + 0x10)          // first field of struct pointed by a1 is a pointer

Record format:

offset=0x00, size=8, access=read/write, type=QWORDoffset=0x08, size=4, access=read, type=DWORD...

Step 3: Traverse Callers for Analysis

Read each caller function and analyze:

1. Parameter passing: What is passed when calling?

   c

   sub_401000(v1);        // v1 might be a struct pointersub_401000(&v2);       // v2 is a structsub_401000(malloc(64)); // struct size is ~64 bytes

2. Operations before/after the call:

   c

   v1 = malloc(0x40);     // allocate 0x40 bytes*v1 = 0;               // offset 0x00 initialization*(v1 + 8) = callback;  // offset 0x08 is a function pointersub_401000(v1);

3. Collect more offset accesses

Step 4: Traverse Callees for Analysis

Read each callee function and analyze:

1. How parameters are used:

   c

   // In calleeint callee(void *a1) {    return *(a1 + 0x18);  // accesses offset 0x18}

2. Passed to other functions:

   c

   another_func(a1 + 0x20);  // offset 0x20 might be a nested struct

Step 5: Aggregate and Infer

1. Merge all offset information, sort by offset
2. Calculate struct size: max(offset) + last_field_size
3. Infer field types:
   • Called as function pointer → function pointer
   • Passed to strlen/printf → string pointer
   • Compared with constants → enum/flags
   • Increment/decrement operations → counter/index
4. Identify common patterns:
   • Offset 0 is a function pointer table → vtable (C++ object)
   • next/prev pointers → linked list node
   • refcount field → reference counted object

Output Format

/* * Structure Recovery Analysis * Source function: <func_address> * Analysis scope: <number of callers/callees analyzed> *  * Functions using this struct: *   - 0x401000 (initialization) *   - 0x401100 (field access) *   - 0x401200 (destruction) */
// Estimated size: 0x48 bytes// Confidence: High / Medium / Low
struct suggested_name {    /* 0x00 */ void *vtable;           // vtable pointer, called: (*(*this))()    /* 0x08 */ int refcount;           // reference count, has ++/-- operations    /* 0x0C */ int flags;              // flags, AND with 0x1, 0x2    /* 0x10 */ char *name;             // string, passed to strlen/printf    /* 0x18 */ void *data;             // data pointer    /* 0x20 */ size_t size;            // size field    /* 0x28 */ struct node *next;      // linked list next pointer    /* 0x30 */ struct node *prev;      // linked list prev pointer    /* 0x38 */ callback_fn handler;    // callback function    /* 0x40 */ void *user_data;        // user data};
// Field access examples:// 0x401000: *(this + 0x08) += 1;     // refcount++// 0x401100: printf("%s", *(this + 0x10));  // print name