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Man Pages

Manual Reference Pages  -  MACH-SYMBOL (3)


symopen, symclose, findhdr, indexsym, lookupsym, findsym, findexsym, flookupsym, ffindsym, lookuplsym, indexlsym, findlsym, symoff, pc2file, file2pc, line2pc, fnbound, fileline, pc2line - symbol table access functions




#include <u.h>
#include <libc.h>
#include <mach.h>

int     symopen(Fhdr *hdr)
void    symclose(Fhdr *hdr)
Fhdr    *findhdr(char *name)
extern  Fhdr* fhdrlist;

int     indexsym(uint n, Symbol *s)
int     lookupsym(char *fn, char *var, Symbol *s)
int     findsym(Loc loc, uint class, Symbol *s)

int     findexsym(Fhdr *hdr, uint n, Symbol *s)
Symbol  *flookupsym(Fhdr *hdr, char *name)
Symbol  *ffindsym(Fhdr *hdr, Loc loc, uint class)

int     indexlsym(Symbol *s1, uint n, Symbol *s2)
int     lookuplsym(Symbol *s1, char *name, Symbol *s2)
int     findlsym(Symbol *s1, Loc loc, Symbol *s2)

int     symoff(char *a, uint n, ulong addr, uint class)

int     pc2file(ulong pc, char *file, uint n, ulong *line)
int     pc2line(ulong pc, ulong *line)
int     fileline(ulong pc, char *buf, uint n)
int     file2pc(char *file, ulong line, ulong *pc)
int     line2pc(ulong basepc, ulong line, ulong *pc)
int     fnbound(ulong pc, ulong bounds[2])


These functions provide machine-independent access to the symbol table of an executable file or executing process. Mach(3), mach-file(3), and mach-map(3) describe additional library functions for accessing executable files and executing processes.

Symopen uses the data in the Fhdr structure filled by crackhdr (see mach-file(3)) to initialize in-memory structures used to access the symbol tables contained in the file. Symclose frees the structures. The rest of the functions described here access a composite symbol table made up of all currently open tables.

The set of all currently open Fhdrs is maintained as a linked list starting at fhdrlist (chained via

Findhdr searches the currently open Fhdrs for one whose file name ends with the path name (that is, matches /usr/lib/ but not

The Symbol data structure:
typedef struct Symbol Symbol;
struct Symbol
        char  *name;
        Loc   loc;
        Loc   hiloc;
        char  class;
        char  type;

describes a symbol table entry. The value field contains the offset of the symbol within its address space: global variables relative to the beginning of the data segment, text beyond the start of the text segment, and automatic variables and parameters relative to the stack frame. The type field contains the type of the symbol:
T text segment symbol
t static text segment symbol
D data segment symbol
d static data segment symbol
B bss segment symbol
b static bss segment symbol
a automatic (local) variable symbol
p function parameter symbol
U undefined symbol
The class field assigns the symbol to a general class; CTEXT, CDATA, CAUTO, and CPARAM are the most popular.

Indexsym stores information for the n th symbol into s. The symbols are ordered by increasing address.

Lookupsym fills a Symbol structure with symbol table information. Global variables and functions are represented by a single name; local variables and parameters are uniquely specified by a function and variable name pair. Arguments fn and var contain the name of a function and variable, respectively. If both are non-zero, the symbol table is searched for a parameter or automatic variable. If only var is zero, the text symbol table is searched for function fn. If only fn is zero, the global variable table is searched for var.

Findsym returns the symbol table entry of type class stored near addr. The selected symbol is a global variable or function with address nearest to and less than or equal to addr. Class specification CDATA searches only the global variable symbol table; class CTEXT limits the search to the text symbol table. Class specification CANY searches the text table first, then the global table.

Findexsym, flookupsym, and ffindsym are similar to indexsym, lookupsym, and findsym, but operate only on the symbols from hdr. Flookupsym and ffindsym return pointers to data stored in the hdr, which must not be modified or freed.

Indexlsym, lookuplsym, and findlsym are similar to indexsym, lookupsym, and findsym, but operate on the smaller symbol table of parameters and variables local to the function represented by symbol s1.

Indexlsym writes symbol information for the nth local symbol of function s1 to s2. Function parameters appear first in the ordering, followed by local symbols.

Lookuplsym writes symbol information for the symbol named name in function s1 to s2.

Findlsym searches for a symbol local to the function s1 whose location is exactly loc, writing its symbol information to s2. Loc is almost always an indirection through a frame pointer register; the details vary from architecture to architecture.

Symoff converts a location to a symbol reference. The string containing that reference is of the form ‘name+offset’, where ‘name’ is the name of the nearest symbol with an address less than or equal to the target address, and ‘offset’ is the hexadecimal offset beyond that symbol. If ‘offset’ is zero, only the name of the symbol is printed. If no symbol is found within 4096 bytes of the address, the address is formatted as a hexadecimal address. Buf is the address of a buffer of n bytes to receive the formatted string. Addr is the address to be converted. Type is the type code of the search space: CTEXT, CDATA, or CANY. Symoff returns the length of the formatted string contained in buf.

Pc2file searches the symbol table to find the file and line number corresponding to the instruction at program counter pc. File is the address of a buffer of n bytes to receive the file name. Line receives the line number.

Pc2line is like pc2file but neglects to return information about the source file.

Fileline is also like pc2file, but returns the file and line number in the n-byte text buffer buf, formatted as ‘file:line’.

File2pc performs the opposite mapping: it stores in pc a text address associated with line line in file file.

Line2pc is similar: it converts a line number to an instruction address, storing it in pc. Since a line number does not uniquely identify an instruction (e.g., every source file has line 1), basepc specifies a text address from which the search begins. Usually this is the address of the first function in the file of interest.

Fnbound returns the start and end addresses of the function containing the text address supplied as the first argument. The second argument is an array of two unsigned longs; fnbound places the bounding addresses of the function in the first and second elements of this array. The start address is the address of the first instruction of the function; the end address is the first address beyond the end of the target function.

All functions return 0 on success and -1 on error. When an error occurs, a message describing it is stored in the system error buffer where it is available via errstr.




mach(3), mach-file(3), mach-map(3)
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