term% cat index.txt MACH(2) System Calls Manual MACH(2)
NAME
crackhdr, machbytype, machbyname, newmap, setmap, unusemap, loadmap,
findseg, get1, get2, get4, put1, put2, put4, beswab, beswal, leswab,
leswal - machine-independent executable file access
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <mach.h>
int crackhdr(int fd, Fhdr *fp)
void machbytype(int type)
int machbyname(char *name)
Map *newmap(Map *map, int fd, int n)
int setmap(Map *map, ulong base, ulong end, ulong foffset,
char *name)
void unusemap(Map *map, int seg)
Map *loadmap(Map *map, int fd, Fhdr *fp)
int findseg(Map *map, char *name)
int get1(Map *map, ulong addr, uchar *buf, int n)
int get2(Map *map, ulong addr, ushort *val)
int get4(Map *map, ulong addr, long *val)
int put1(Map *map, ulong addr, uchar *buf, int n)
int put2(Map *map, ulong addr, ushort val)
int put4(Map *map, ulong addr, long val)
ushort beswab(ushort val)
long beswal(long val)
ushort leswab(ushort val)
long leswal(long val)
extern Mach mach;
extern Machdata machdata;
DESCRIPTION
These functions provide machine-independent access to an executable
file or executing process image. The latter is accessed by opening ei‐
ther /proc/pid/text or /proc/pid/mem as described in proc(3). Sym‐
bol(2) and object(2) describe other library functions for machine-inde‐
pendent access to symbol tables and object files.
Crackhdr loads data structure fp with a machine-independent description
of the header of the executable file or image associated with the open
file descriptor fd. It also sets global variable mach pointing to the
Mach data structure containing the machine-dependent parameters of the
target architecture.
Machbytype and machbyname select the data structures and parameter val‐
ues associated with the specified architecture. The former selects the
architecture based on the code stored in the field named type in the
Fhdr data structure. The latter selects a processor class by name; one
of 68020, mips, mipsco, sparc, sunsparc, 386, 86, or 960. These func‐
tions point the mach and machdata global variables to the proper Mach
and Machdata data structures and load global variable asstype with the
disassembler type code.
A map is a data structure used to transform an address in the address
space of an executable to an offset in a file or executing image. A
map comprises one or more segments, each associating a range of ad‐
dresses with an offset in the file or memory image. The range of one
segment may not overlap the range of another segment in the map. Most
maps define segments named `text' and `data' to map the instruction and
initialized data sections of an executable file. When the map is asso‐
ciated with the memory image of an executing program, the range of the
`data' segment is usually extended to include the bss, heap, and stack
of the process and an additional segment, named `ublock', maps the page
containing the saved registers and process state information.
Newmap creates a map with n segments or recycles a map currently in
use. If map is zero, a new map is dynamically allocated, otherwise it
is assumed to point to an existing dynamically allocated map whose size
is adjusted, as necessary. The map is associated with the open file
descriptor fd and all segments are marked as unused. The address of
the map is returned. A zero return indicates an allocation error.
Setmap loads the first unused segment in map with the segment mapping
parameters. Base and end contain the lowest and highest virtual ad‐
dresses mapped by the segment. Foffset contains the offset in the exe‐
cutable to the start of the segment. Name is a name to be attached to
the segment.
Unusemap marks segment number seg in map map unused. Other segments in
the map remain unaffected.
Loadmap uses the values in a Fhdr data structure (usually filled by
crackhdr) to initialize a default map for an executable file or execut‐
ing image. If map is zero, a new map with two segments is dynamically
allocated; otherwise, map is initialized with the appropriate values.
This function returns the address of the map if successful, zero on
failure. Two segments, named `text' and `data' are defined in the map;
they map the instruction and initialized data sections of the program
described by the Fhdr structure.
Get1, get2, and get4 retrieve the data stored at address addr in the
program file or executable image associated with map. Get1 retrieves n
bytes of data beginning at addr into buf. Get2 and get4 retrieve
16-bit and 32-bit values respectively, into the location pointed to by
val. The value is byte-swapped if the source byte order differs from
that of the current architecture. This implies that the value returned
by get4 may not be the same as the four-byte sequence returned by get1
when n is four; the former may be byte-swapped, the latter is indepen‐
dent of source and target byte order. If the file descriptor associ‐
ated with map is negative, the address itself is placed in the return
location. These functions return the number of bytes read. A -1 indi‐
cates an error condition.
Put1, put2, and put4 write to the file or executing image associated
with map. The address is translated using the map parameters and
multi-byte quantities are byte-swapped, if necessary, before they are
written. Put1 transfers n bytes stored at buf; put2 and put4 write the
16-bit and 32-bit quantity contained in val, respectively. The number
of bytes transferred is returned. A -1 return value indicates an er‐
ror.
Beswab and beswal return the ushort and long big-endian representation
of val, respectively. Leswab and leswal return the little-endian rep‐
resentation of the ushort and long contained in val.
SOURCE
/sys/src/libmach
SEE ALSO
symbol(2), object(2), errstr(2), proc(3), a.out(6)
DIAGNOSTICS
These routines set errstr.
MACH(2)