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#include <stab.h>
/* * Format of a symbol table entry. */struct nlist { union { const char *n_name; /* for use when in-core */ long n_strx; /* index into file string table */ } n_un; unsigned char n_type; /* type flag */ char n_other; /* unused */ short n_desc; /* see struct desc, below */ unsigned n_value; /* address or offset or line */ };
The low bits of the n_type field are used to place a symbol into at most one segment, according to the following masks, defined in <a.out.h>. A symbol can be in none of these segments by having none of these segment bits set.
/* * Simple values for n_type. */#define N_UNDF 0x0 /* undefined */ #define N_ABS 0x2 /* absolute */ #define N_TEXT 0x4 /* text */ #define N_DATA 0x6 /* data */ #define N_BSS 0x8 /* bss */
#define N_EXT 01 /* external bit, or'ed in */
The n_value field of a symbol is relocated by the linker, ld(1) as an address within the appropriate segment. N_value fields of symbols not in any segment are unchanged by the linker. In addition, the linker will discard certain symbols, according to rules of its own, unless the n_type field has one of the following bits set:
/* * Other permanent symbol table entries have some of the N_STAB bits set. * These are given in <stab.h> */#define N_STAB 0xe0 /* if any of these bits set, don't discard */
This allows up to 112 (7 * 16) symbol types, split between the various segments. Some of these have already been claimed. The old symbolic debugger, sdb, uses the following n_type values:
#define N_GSYM 0x20 /* global symbol: name,,0,type,0 */ #define N_FNAME 0x22 /* procedure name (f77 kludge): name,,0 */ #define N_FUN 0x24 /* procedure: name,,0,linenumber,address */ #define N_STSYM 0x26 /* static symbol: name,,0,type,address */ #define N_LCSYM 0x28 /* .lcomm symbol: name,,0,type,address */ #define N_RSYM 0x40 /* register sym: name,,0,type,register */ #define N_SLINE 0x44 /* src line: 0,,0,linenumber,address */ #define N_SSYM 0x60 /* structure elt: name,,0,type,struct_offset */ #define N_SO 0x64 /* source file name: name,,0,0,address */ #define N_LSYM 0x80 /* local sym: name,,0,type,offset */ #define N_SOL 0x84 /* #included file name: name,,0,0,address */ #define N_PSYM 0xa0 /* parameter: name,,0,type,offset */ #define N_ENTRY 0xa4 /* alternate entry: name,linenumber,address */ #define N_LBRAC 0xc0 /* left bracket: 0,,0,nesting level,address */ #define N_RBRAC 0xe0 /* right bracket: 0,,0,nesting level,address */ #define N_BCOMM 0xe2 /* begin common: name,, */ #define N_ECOMM 0xe4 /* end common: name,, */ #define N_ECOML 0xe8 /* end common (local name): ,,address */ #define N_LENG 0xfe /* second stab entry with length information */
where the comments give sdb conventional use for .stab s and the n_name, n_other, n_desc, and n_value fields of the given n_type. Sdb uses the n_desc field to hold a type specifier in the form used by the Portable C Compiler, cc(1); see the header file pcc.h for details on the format of these type values.
The Berkeley Pascal compiler, pc(1), uses the following n_type value:
#define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */
and uses the following subtypes to do type checking across separately compiled files:
1 source file name 2 included file name 3 global label 4 global constant 5 global type 6 global variable 7 global function 8 global procedure 9 external function 10 external procedure 11 library variable 12 library routine
STAB (5) | June 10, 2010 |
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