E32Image file format on Symbian OS 9

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This article explains briefly the E32Image file format on Symbian OS v9 or newer. Please check some links at the end of this article for more detailed information.

Introduction

The executable files on Symbian OS v9, i.e., .exe or .dll, use a special format, called E32Image. It is based on ELF file format. It is different on pre-Symbian OS v9. The E32Image on pre-Symbian OS v9 is based on PE file format.

E32Image added some Symbian-specific information to the header. It also replaces function names with ordinal numbers. The tool used to translate ELF into E32Image is called elftran and elf2e32.

The difference between elftran and elf2e32 is the input file. The elftran tool translates ELF file in ABIv1 format into E32Image. The elf232 translates ELF file in newer format, ABIv2, into E32Image.

Like standard ELF executable file, E32Image contains of several sections, i.e.:

Code section. It contains three parts: text section, export address table and import address table.
BSS section. It contains un-initialized data.
Data section. It contains initialized data.
Import section. It contains the information about all imported functions used by the code.
Relocation section. It contains relocation table needed by Symbian OS loader to load the code.

Header information

The header information of E32Image is defined in a header file called f32image.h. It is part of the public Symbian SDKs located at \epoc32\include. The declaration of the header is splitted into three parts.

The first part, E32ImageHeader, is the main part. It is quite similar to the header on pre-Symbian OS 9.

class E32ImageHeader
	{
public:
	TUint32	iUid1;
	TUint32	iUid2;
	TUint32	iUid3;
	TUint32 iUidChecksum;
	TUint iSignature;
	TUint32	iHeaderCrc;
	TUint32 iModuleVersion;
	TUint32 iCompressionType;
	TVersion iToolsVersion;
	TUint32 iTimeLo;
	TUint32 iTimeHi;
	TUint iFlags;
	TInt iCodeSize;
	TInt iDataSize;
	TInt iHeapSizeMin;
	TInt iHeapSizeMax;
	TInt iStackSize;
	TInt iBssSize;
	TUint iEntryPoint;
	TUint iCodeBase;
	TUint iDataBase;
	TInt iDllRefTableCount;
	TUint iExportDirOffset;
	TInt iExportDirCount;
	TInt iTextSize;
	TUint iCodeOffset;
	TUint iDataOffset;
	TUint iImportOffset;
	TUint iCodeRelocOffset;
	TUint iDataRelocOffset;
	TUint16 iProcessPriority;
	TUint16 iCpuIdentifier;
	};

The second part, E32ImageHeaderComp is needed when the executable file is compressed.

class E32ImageHeaderComp : public E32ImageHeader
	{
public:
	TUint32 iUncompressedSize;
	};

The third part, E32ImageHeaderV contains some extra information.

class E32ImageHeaderV : public E32ImageHeaderComp
	{
public:
	SSecurityInfo iS;
	TUint32 iExceptionDescriptor;
	TUint32 iSpare2;
	TUint16	iExportDescSize;
	TUint8	iExportDescType;
	TUint8	iExportDesc[1];
	};

E32ImageHeader

iUid1, iUid2, iUid3, are the first, second and third UIDs of the executable file respectively.
iUidChecksum, is the checksum of the first three UIDs.
iSignature, is a unique signature of E32 file, always has a value of 'EPOC'.
iHeaderCrc, is the checksum of entire header, calculated with CCITT CRC-32 algorithm.
iModuleVersion, is the version number for this executable.
iCompressionType, is the UID of the library used to compress the executable file. It is 0 if the executable is not compressed or KUidCompressionDeflate (=0x101F 7AFC) if it is compressed with Deflate algorithm.
iToolsVersion, is the version of ELFTRAN that generates this file.
iTimeLo, iTimeHi, is the lowest and highest word of the timestamp when the file is created respectively.
iFlags, flags for this executable. There are some flags defined in f32image.h, for example, KImageDll, KImageNoCallEntryPoint, etc.
iCodeSize, is the size of code section, import address table, constant data and export dir.
iDataSize, is size of initialized data.
iHeapSizeMin, is the minimum size of the heap.
iHeapSizeMax, is the maximum size of the heap.
iStackSize, is the size of the stack.
iBssSize, is the size of the un-initialized data section.
iEntryPoint, is the offset into code of entry point.
iCodeBase, where the code is linked for.
iDataBase, where the data is linked for.
iDllRefTableCount, is the number of DLLs imported by this program.
iExportDirOffset, is the offset into the file of the export address table.
iExportDirCount, is the offset of the export address table.
iTextSize, is size of just the text section.
iCodeOffset, is the file offset to code section.
iDataOffset, is the file offset to data section.
iImportOffset, is the file offset to import section.
iCodeRelocOffset, is the relocations for code and constants.
iDataRelocOffset, is the relocations for data.
iProcessPriority, is the executables priority.
iCpuIdentifier, is the identifier of CPU.

E32ImageHeaderComp

iUncompressedSize, the uncompressed size of file. Remember that E32Image file might be compressed.

E32ImageHeaderV

iS.iSecureId, is secure ID of the executable. It is usually the same as the UID3 of the executable.
iS.iVendorId, is vendor ID of executable. For third party application, it is usually 0.
iS.iCaps.iCaps, is capabilities needed to run the executable. The definition of all Symbian OS capabilities can be found at e32capability.h.
iExceptionDescriptor, is the offset in bytes from start of code section to Exception Descriptor, bit 0 set if valid
iSpare2, reserved.
iExportDescSize, is the size of bitmap section.
iExportDescType[1], is type of description of holes in export table.
iExportDesc[1], is the description of holes in export table.

Internal links

External links

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