#ifndef _NTPSAPI_H

//
// Process information structures
//

typedef struct _PEB_LDR_DATA
{
    ULONG Length;
    BOOLEAN Initialized;
    HANDLE SsHandle;
    LIST_ENTRY InLoadOrderModuleList;
    LIST_ENTRY InMemoryOrderModuleList;
    LIST_ENTRY InInitializationOrderModuleList;
    PVOID EntryInProgress;
    BOOLEAN ShutdownInProgress;
    HANDLE ShutdownThreadId;
} PEB_LDR_DATA, *PPEB_LDR_DATA;

#endif
View code on GitHub

This structure is documented in Windows SDK.

Length

Size of structure, used by ntdll.dll as structure version ID.

Initialized

If set, loader data section for current process is initialized.

SsHandle

???

InLoadOrderModuleList

Doubly linked list containing pointers to LDR_MODULE structure for previous and next module in load order.

InMemoryOrderModuleList

As above, but in memory placement order.

InInitializationOrderModuleList

As InLoadOrderModuleList, but in initialization order.

Documented by

ReactOS
Tomasz Nowak

PEB_LDR_DATA - NtDoc