The section table and section data of a PE32 file

A PE file keeps its code and data in sections. The section table, straight after the optional header, has one entry for each section, NumberOfSections in all. Each entry says where the section goes in memory, where its bytes are in the file, and what may be done with it: read, write or execute.

The section header

IMAGE_SECTION_HEADER, 40 bytes:

Offset	Size	Type	Field	Meaning
0	8	char[8]	Name	The name, padded with zero bytes, with no terminator when it is 8 characters long; see Names.
8	4	u32	VirtualSize	The size of the section in memory. When it is larger than SizeOfRawData, the rest is filled with zeros.
12	4	u32	VirtualAddress	The RVA of its first byte, a multiple of SectionAlignment.
16	4	u32	SizeOfRawData	The size of its data in the file, a multiple of FileAlignment.
20	4	u32	PointerToRawData	The file offset of its data, a multiple of FileAlignment; 0 when it has none.
24	4	u32	PointerToRelocations	0 in images (COFF relocations are for object files).
28	4	u32	PointerToLinenumbers	0; COFF line numbers are deprecated.
32	2	u16	NumberOfRelocations	0 in images.
34	2	u16	NumberOfLinenumbers	0.
36	4	u32	Characteristics	Flags; see Flags.

000001F0                          2E 74 65 78 74 00 00 00
00000200  9E 7F 00 00 00 10 00 00 00 80 00 00 00 04 00 00
00000210  00 00 00 00 00 00 00 00 00 00 00 00 20 00 00 60

The first section header of the 32-bit glfw3.dll, at 0x1F8: .text; 0x7F9E bytes in memory at RVA 0x1000; 0x8000 bytes in the file at 0x400; flags 0x60000020: CNT_CODE, MEM_EXECUTE and MEM_READ

That file’s five sections:

Name	RVA	Size in memory	File offset	Size in file	Flags
`.text`	`0x1000`	`0x7F9E`	`0x400`	`0x8000`	`0x60000020` code, read, execute
`.rdata`	`0x9000`	`0x2B04`	`0x8400`	`0x2C00`	`0x40000040` data, read
`.data`	`0xC000`	`0xCE4`	`0xB000`	`0x200`	`0xC0000040` data, read, write
`.rsrc`	`0xD000`	`0x1B4`	`0xB200`	`0x200`	`0x40000040` data, read
`.reloc`	`0xE000`	`0x86C`	`0xB400`	`0xA00`	`0x42000040` data, read, discardable

.data is 0xCE4 bytes in memory but only 0x200 in the file: the rest is uninitialised data, which the loader fills with zeros.

Names

The name is 8 bytes. A longer name is written as / and a decimal number: the offset of the full name in the COFF string table. Microsoft’s linker truncates long names in images instead, but MinGW and Wine files use the long form, such as /4 for .debug_info. The loader finds the tables through the data directories, not by section name.

Names seen most in the files examined for this site:

Name	Usually holds
`.text`	Code. Borland’s linkers call it `CODE`.
`.rdata`	Read-only data: constants, the import and export tables, the debug directory and the load configuration.
`.data`	Initialised writable data. Borland: `DATA`; Watcom: `DGROUP` and `AUTO`.
`.bss`	Uninitialised data, with no bytes in the file. Borland: `BSS`.
`.idata`	The import tables, in files from older and non-Microsoft linkers.
`.edata`	The export tables, likewise.
`.rsrc`	The resources.
`.reloc`	The base relocations.
`.pdata`	The exception table, on machines that have one.
`.tls`	The thread-local storage template.
`.CRT`	The C run-time library’s initialiser lists.
`.debug_*`	DWARF debug information (MinGW and Wine).
`.rodata`, `.eh_frame`	Read-only data and unwind tables in GNU-built files.

Rarer names include .E32_UID in Symbian emulator DLLs and .nv_fatb, NVIDIA’s CUDA fat binaries.

Flags

Bit	Name	Meaning
`0x00000008`	TYPE_NO_PAD	Obsolete.
`0x00000020`	CNT_CODE	Holds executable code.
`0x00000040`	CNT_INITIALIZED_DATA	Holds initialised data.
`0x00000080`	CNT_UNINITIALIZED_DATA	Holds uninitialised data.
`0x00000100`	LNK_OTHER	Reserved.
`0x00000200`	LNK_INFO	Comments or other information (object files).
`0x00000800`	LNK_REMOVE	Not to become part of the image (object files).
`0x00001000`	LNK_COMDAT	COMDAT data (object files).
`0x00008000`	GPREL	Data referred to through the global pointer.
`0x00020000`	MEM_PURGEABLE, MEM_16BIT	Reserved.
`0x00040000`	MEM_LOCKED	Reserved.
`0x00080000`	MEM_PRELOAD	Reserved.
`0x00100000`–`0x00E00000`	ALIGN_1BYTES … ALIGN_8192BYTES	Alignment of the section’s data, in object files only.
`0x01000000`	LNK_NRELOC_OVFL	More COFF relocations than fit in NumberOfRelocations (object files).
`0x02000000`	MEM_DISCARDABLE	Can be discarded once loaded, as `.reloc` is.
`0x04000000`	MEM_NOT_CACHED	Cannot be cached.
`0x08000000`	MEM_NOT_PAGED	Cannot be paged out.
`0x10000000`	MEM_SHARED	Shared between every process that loads the image.
`0x20000000`	MEM_EXECUTE	Can be executed.
`0x40000000`	MEM_READ	Can be read.
`0x80000000`	MEM_WRITE	Can be written.

Section data

Each section’s bytes are at PointerToRawData, SizeOfRawData long, after the headers and in the order of the section table. The loader maps each one to ImageBase + VirtualAddress, and zero-fills the memory from SizeOfRawData up to VirtualSize. The headers themselves are loaded at RVA 0, SizeOfHeaders long.

Mapping an RVA to a file offset. Find the section with VirtualAddress ≤ RVA < VirtualAddress + max(VirtualSize, SizeOfRawData). The file offset is PointerToRawData + (RVA − VirtualAddress), and it has bytes in the file only while RVA − VirtualAddress < SizeOfRawData. An RVA below the first section is in the headers, and its file offset is the RVA itself. In the example, the export directory at RVA 0xA490 is in .rdata, so it is at 0x8400 + (0xA490 − 0x9000) = 0x9890 in the file.

The explorer shows each section’s raw data as one part, in file order. Inside it are the tables that lie there, then the bytes no table covers: “Code” in a section with CNT_CODE or MEM_EXECUTE, which is disassembled, and “Data” in the others. The bytes after VirtualSize, up to SizeOfRawData, are “Alignment padding”. In the 32-bit glfw3.dll, .rdata holds the import address tables, the debug directory, the load configuration, the SafeSEH table, the POGO debug data, the export tables and the import descriptors, with data between them.

A PointerToRawData of 0 means the section has no data in the file, whatever SizeOfRawData says. Watcom’s linker gives .bss a SizeOfRawData but a pointer of 0.
The Windows loader rounds PointerToRawData down to a multiple of 512, and some packers rely on it. The explorer does not round, so such files are laid out as written.
A section whose data lies inside an earlier part, or runs past the end of the file, is reported. In the files examined for this site, truncated downloads were one cause.

.EXE File Format – Section table and section data

The section header

Names

Flags

Section data