typedef struct {
  union {
    char e_name[E_SYMNMLEN];
    struct {
      unsigned long e_zeroes;
      unsigned long e_offset;
    } e;
  } e;
  unsigned long e_value;
  short e_scnum;
  unsigned short e_type;
  unsigned char e_sclass;
  unsigned char e_numaux;
} SYMENT;

The symbol table is probably one of the most complex parts of the COFF object, mostly because there are so many symbol types. The symbol table has entries for all symbols and meta-symbols, including public, static, external, section, and debugging symbols.

e.e_name - inlined symbol name

If the symbol's name is eight characters or less, it is stored in this field. Note that the first character overlaps the e_zeroes field - by doing so, the e_zeroes field can be used to determine if the symbol name has been inlined. Beware that the name is null terminated only if it is less than eight characters long, else it is not null terminated.

e.e.e_zeroes - flag to tell if name is inlined

If this field is zero, then the symbol name is found by using e_offset as an offset into the string table. If it is nonzero, then the name is in the e_name field.

e.e.e_offset - offset of name in string table

If e_zeroes is zero, this field contains the offset of the symbol name in the string table.

e_value - the value of the symbol

The value of the symbol. For example, if the symbol represents a function, this contains the address of the function. The meaning of the value depends on the type of symbol (below).

e_scnum - section number

The number of the section that this symbol belongs to. The first section in the section table is section one. In addition, e_scnum may be one of the following values:

Symbol	Value	Meaning
N_UNDEF	0	An undefined (extern) symbol
N_ABS	-1	An absolute symbol (e_value is a constant, not an address)
N_DEBUG	-2	A debugging symbol

e_type - symbol type

The type of the symbol. This is made up of a base type and a derived type. For example, "pointer to int" is "pointer to T" and "int".

Type	Bits	Meaning
T_NULL	---- 0000	No symbol
T_VOID	---- 0001	void function argument (not used)
T_CHAR	---- 0010	character
T_SHORT	---- 0011	short integer
T_INT	---- 0100	integer
T_LONG	---- 0101	long integer
T_FLOAT	---- 0110	floating point
T_DOUBLE	---- 0111	double precision float
T_STRUCT	---- 1000	structure
T_UNION	---- 1001	union
T_ENUM	---- 1010	enumeration
T_MOE	---- 1011	member of enumeration
T_UCHAR	---- 1100	unsigned character
T_USHORT	---- 1101	unsigned short
T_UINT	---- 1110	unsigned integer
T_ULONG	---- 1111	unsigned long
T_LNGDBL	---1 0000	long double (special case bit pattern)
DT_NON	--00 ----	No derived type
DT_PTR	--01 ----	pointer to T
DT_FCN	--10 ----	function returning T
DT_ARY	--11 ----	array of T

The BTYPE(x) macro extracts the base type from e_type. Note that all DT_* must be shifted by N_BTSHIFT to get actual values, as in:

e_type = base + derived << N_BTSHIFT;

There are also macros ISPTR, ISFCN, and ISARY that test the upper bits for the derived type.

e_sclass - storage class

This tells where and what the symbol represents.

Class	Value	Meaning
C_NULL	0	No entry
C_AUTO	1	Automatic variable
C_EXT	2	External (public) symbol - this covers globals and externs
C_STAT	3	static (private) symbol
C_REG	4	register variable
C_EXTDEF	5	External definition
C_LABEL	6	label
C_ULABEL	7	undefined label
C_MOS	8	member of structure
C_ARG	9	function argument
C_STRTAG	10	structure tag
C_MOU	11	member of union
C_UNTAG	12	union tag
C_TPDEF	13	type definition
C_USTATIC	14	undefined static
C_ENTAG	15	enumaration tag
C_MOE	16	member of enumeration
C_REGPARM	17	register parameter
C_FIELD	18	bit field
C_AUTOARG	19	auto argument
C_LASTENT	20	dummy entry (end of block)
C_BLOCK	100	".bb" or ".eb" - beginning or end of block
C_FCN	101	".bf" or ".ef" - beginning or end of function
C_EOS	102	end of structure
C_FILE	103	file name
C_LINE	104	line number, reformatted as symbol
C_ALIAS	105	duplicate tag
C_HIDDEN	106	ext symbol in dmert public lib
C_EFCN	255	physical end of function

e_numaux - number of auxiliary entries

Each symbol is allowed to have additional data that follows it in the symbol table. This field tells how many equivalent SYMENTs are used for aux entries. For most symbols, this is zero. A value of one allows up to SYMESZ bytes of auxiliary information for that symbol. A non-exhaustive list of auxiliary entries follows, based on the storage class (e_sclass) or type (e_type) of the symbol.

Auxiliary Entries

DT_ARY

.x_sym.x_misc.x_lnsz.x_size

size in bytes (size*count)

T_STRUCT

T_UNION

T_ENUM

.x_sym.x_tagndx

syment index for list of tags (will point to C_STRTAG, C_UNTAG, or C_ENTAG)

.x_sym.x_misc.x_lnsz.x_size

size in bytes (size*count)

T_NULL | C_STAT - section symbols (like .text)

.x_scn.x_scnlen

section length (bytes)

.x_scn.x_nreloc

number of relocation entries (ushort)

.x_scn.x_nlinno

number of line numbers (ushort)

C_STRTAG - will be followed by C_MOS's and C_EOS

C_UNTAG - will be followed by C_MOU's and C_EOS

C_ENTAG - will be followed by C_MOE's and C_EOS

.x_sym.x_x_misc.x_lnsz.x_size

The size of the struct/union/enum

.x_sym.x_fcnary.x_fcn.x_endndx

The symbol index after our list.

C_EOS

.x_sym.x_misc.x_lnsz.x_size

the size of the struct/union/enum

.x_sym.x_tagndx

The symbol index of the start of our list.

C_FIELD

.x_sym.x_x_misc.x_lnsz.x_size

the number of bits

C_BLOCK

.x_sym.x_misc.x_lnsz.x_lnno

starting line number

.x_sym.x_fcnary.x_fcn.x_endndx

The symbol index after our block (if .bb)

C_FCN

.x_sym.x_misc.x_lnsz.x_lnno

starting line number

.x_sym.x_misc.x_lnsz.x_size

size in bytes

C_FILE

.x_file.x_fname

.x_file.x_n.x_zeroes

.x_file.x_n.x_offset

These three specify the file name, just like the three fields used to specify the symbol name.

Meanings of the Values