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NAME
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symopen, symclose, findhdr, indexsym, lookupsym, findsym, findexsym,
flookupsym, ffindsym, lookuplsym, indexlsym, findlsym, symoff,
pc2file, file2pc, line2pc, fnbound, fileline, pc2line – symbol
table access functions
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SYNOPSIS
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#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])
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DESCRIPTION
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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 Fhdr.next).
Findhdr searches the currently open Fhdrs for one whose file name
ends with the path name (that is, libc.so matches /usr/lib/libc.so
but not mylibc.so).
The Symbol data structure:
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typedef struct Symbol Symbol;
struct Symbol
{
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char *name;
Loc loc;
Loc hiloc;
char class;
char type;
...
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};
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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:
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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
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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.
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SOURCE
SEE ALSO
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