MACH(2) 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)
Page 1 Plan 9 (printed 12/21/24)
MACH(2) MACH(2)
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 invokes 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
application invokes functions to construct one or more maps,
data structures 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 interface to the processor-dependent data.
Crackhdr interprets the header of the executable associated
with the open file descriptor fd. It loads the data struc-
ture fp with a machine-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
Page 2 Plan 9 (printed 12/21/24)
MACH(2) MACH(2)
8c(1) for a list of valid names. Both functions point glo-
bal 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 necessary. A zero return value
indicates an allocation error.
Setmap loads the first unused segment in map with the seg-
ment mapping parameters. Fd is an open file descriptor
associated with an executable. Base and end contain the
lowest and highest virtual addresses mapped by the segment.
Foffset is the offset to the start of the segment 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 return 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 described in the Fhdr structure pointed to
by fp. Usually that structure was loaded by crackhdr and can
be passed to this function without modification. If map is
non-zero, that map, which must have been dynamically allo-
cated, 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 executable, for example, an executable program
file.
Attachproc constructs a map for accessing a running process.
It returns 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 seg-
ment extends to the top of the stack or 0x7fffffff if the
Page 3 Plan 9 (printed 12/21/24)
MACH(2) MACH(2)
stack top cannot be found, and the register sets are read-
able 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 beginning 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
negative, the address itself is placed in the return loca-
tion. These functions return the number of bytes read or a
-1 when there is an error.
Put1, put2, put4, and put8 write to the executable associ-
ated 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, put4, and put8 write the 16-bit, 32-bit
or 64-bit quantity contained in val, respectively. The num-
ber of bytes transferred is returned. A -1 return value
indicates an error.
Beswab, beswal, and beswav return the ushort, long, and
vlong big-endian representation of val, respectively.
Leswab, leswal, and leswav return the little-endian repre-
sentation 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.
Page 4 Plan 9 (printed 12/21/24)