term% cat index.txt MACH(2) System Calls Manual MACH(2)
NAME
crackhdr, machbytype, machbyname, newmap, setmap, findseg, unusemap,
loadmap, attachproc, get1, get2, get4, get8, geta, put1, put2, put4,
put8, puta, beswab, beswal, beswav, leswab, leswal, leswav - machine-
independent access to executable files
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 n)
int setmap(Map *map, int fd, ulong base, ulong end,
ulong foffset, char *name)
int findseg(Map *map, char *name)
void unusemap(Map *map, int seg)
Map *loadmap(Map *map, int fd, Fhdr *fp)
Map *attachproc(int pid, int kflag, int corefd, Fhdr *fp)
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 get8(Map *map, ulong addr, vlong *val)
int geta(Map *map, uvlong addr, uvlong *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)
int put8(Map *map, ulong addr, vlong val)
int puta(Map *map, uvlong addr, uvlong val)
ushort beswab(ushort val)
long beswal(long val)
long beswav(vlong val)
ushort leswab(ushort val)
long leswal(long val)
long leswav(vlong val)
extern Mach mach;
extern Machdata machdata;
DESCRIPTION
These functions provide a processor-independent interface for accessing
the executable files or executing images of all architectures. Related
library functions described in symbol(2) and object(2) provide similar
access to symbol tables and object files.
An executable is a file containing an executable program or the text
file of the /proc file system associated with an executing process as
described in proc(3). After opening an executable, an application in‐
vokes a library function which parses the file header, determines the
target architecture and initializes data structures with parameters and
pointers to functions appropriate for that architecture. Next, the ap‐
plication invokes functions to construct one or more maps, data struc‐
tures that translate references in the address space of the executable
to offsets in the file. Each map comprises one or more segments, each
associating a non-overlapping range of memory addresses with a logical
section of the executable. Other library functions then use a map and
the architecture-specific data structures to provide a generic inter‐
face to the processor-dependent data.
Crackhdr interprets the header of the executable associated with the
open file descriptor fd. It loads the data structure fp with a ma‐
chine-independent description of the header information and points
global variable mach to the Mach data structure containing processor-
dependent parameters of the target architecture.
Machbytype selects architecture-specific data structures and parameter
values based on the code stored in the field named type in the Fhdr
data structure. Machbyname performs the same selection based on the
name of a processor class; see 8c(1) for a list of valid names. Both
functions point global variables mach and machdata to the Mach and
Machdata data structures appropriate for the target architecture and
load global variable asstype with the proper disassembler type code.
Newmap creates an empty map with n segments. If map is zero, the new
map is dynamically allocated, otherwise it is assumed to point to an
existing dynamically allocated map whose size is adjusted, as neces‐
sary. A zero return value indicates an allocation error.
Setmap loads the first unused segment in map with the segment mapping
parameters. Fd is an open file descriptor associated with an exe‐
cutable. Base and end contain the lowest and highest virtual addresses
mapped by the segment. Foffset is the offset to the start of the seg‐
ment in the file. Name is a name to be attached to the segment.
Findseg returns the index of the the segment named name in map. A re‐
turn of -1 indicates that no segment matches name.
Unusemap marks segment number seg in map map unused. Other segments in
the map remain unaffected.
Loadmap initializes a default map containing segments named ‘text' and
‘data' that map the instruction and data segments of the executable de‐
scribed in the Fhdr structure pointed to by fp. Usually that structure
was loaded by crackhdr and can be passed to this function without modi‐
fication. If map is non-zero, that map, which must have been dynami‐
cally allocated, is resized to contain two segments; otherwise a new
map is allocated. This function returns zero if allocation fails.
Loadmap is usually used to build a map for accessing a static exe‐
cutable, for example, an executable program file.
Attachproc constructs a map for accessing a running process. It re‐
turns the address of a Map containing segments mapping the address
space of the running process whose process ID is pid. If kflag is non-
zero, the process is assumed to be a kernel process. Corefd is an file
descriptor opened to /proc/pid/mem. Fp points to the Fhdr structure
describing the header of the executable. For most architectures the
resulting Map contains four segments named ‘text', ‘data', ‘regs' and
‘fpregs'. The latter two provide access to the general and floating
point registers, respectively. If the executable is a kernel process
(indicated by a non-zero kflag argument), the data segment extends to
the maximum supported address, currently 0xffffffff, and the register
sets are read-only. In user-level programs, the data segment extends
to the top of the stack or 0x7fffffff if the stack top cannot be found,
and the register sets are readable and writable. Attachproc returns
zero if it is unable to build the map for the specified process.
Get1, get2, get4, and get8 retrieve the data stored at address addr in
the executable associated with map. Get1 retrieves n bytes of data be‐
ginning at addr into buf. Get2, get4 and get8 retrieve 16-bit, 32-bit
and 64-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
get2, get4, and get8 may not be the same as the byte sequences returned
by get1 when n is two, four or eight; the former may be byte-swapped,
the latter reflects the byte order of the target architecture. If the
file descriptor associated with the applicable segment in map is nega‐
tive, the address itself is placed in the return location. These func‐
tions return the number of bytes read or a -1 when there is an error.
Put1, put2, put4, and put8 write to the executable associated with map.
The address is translated using the map parameters and multi-byte quan‐
tities are byte-swapped, if necessary, before they are written. Put1
transfers n bytes stored at buf; put2, put4, and put8 write the 16-bit,
32-bit or 64-bit quantity contained in val, respectively. The number
of bytes transferred is returned. A -1 return value indicates an er‐
ror.
Beswab, beswal, and beswav return the ushort, long, and vlong big-en‐
dian representation of val, respectively. Leswab, leswal, and leswav
return the little-endian representation of the ushort, long, and vlong
contained in val.
SOURCE
/sys/src/libmach
SEE ALSO
8c(1), symbol(2), object(2), errstr(2), proc(3), a.out(6)
DIAGNOSTICS
These routines set errstr.
MACH(2)