man/man3/mach.3

.TH MACH 3
.SH NAME
crackhdr, machbytype, machbyname, newmap, setmap, findseg, unusemap,
loadmap, attachproc, get1, get2, get4, get8, put1, put2, put4, put8,
beswab, beswal, beswav, leswab, leswal, leswav \- machine-independent access to executable files
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.br
.B #include <bio.h>
.br
.B #include <mach.h>
.PP
.ta \w'\fLmachines 'u
.B
int crackhdr(int fd, Fhdr *fp)
.PP
.B
void machbytype(int type)
.PP
.B
int machbyname(char *name)
.PP
.B
Map *newmap(Map *map, int n)
.PP
.B
int setmap(Map *map, int fd, ulong base, ulong end,
.PP
.B
            ulong foffset, char *name)
.PP
.B
int findseg(Map *map, char *name)
.PP
.B
void unusemap(Map *map, int seg)
.PP
.B
Map *loadmap(Map *map, int fd, Fhdr *fp)
.PP
.B
Map *attachproc(int pid, int kflag, int corefd, Fhdr *fp)
.PP
.B
int get1(Map *map, ulong addr, uchar *buf, int n)
.PP
.B
int get2(Map *map, ulong addr, ushort *val)
.PP
.B
int get4(Map *map, ulong addr, long *val)
.PP
.B
int get8(Map *map, ulong addr, vlong *val)
.PP
.B
int put1(Map *map, ulong addr, uchar *buf, int n)
.PP
.B
int put2(Map *map, ulong addr, ushort val)
.PP
.B
int put4(Map *map, ulong addr, long val)
.PP
.B
int put8(Map *map, ulong addr, vlong val)
.PP
.B
ushort beswab(ushort val)
.PP
.B
long beswal(long val)
.PP
.B
long beswav(vlong val)
.PP
.B
ushort leswab(ushort val)
.PP
.B
long leswal(long val)
.PP
.B
long leswav(vlong val)
.PP
.B
extern Mach mach;
.PP
.B
extern Machdata machdata;
.SH DESCRIPTION
These functions provide
a processor-independent interface for accessing
the executable files or executing images of all
architectures.
Related library functions described in
.IR symbol (2)
and
.IR object (2)
provide similar access to symbol tables and object files.
.PP
An
.I executable
is a file containing an executable program or the
.B text
file of the
.B /proc
file system associated with an executing process as
described in
.IR 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
.IR maps ,
data structures that translate references
in the address space of the executable
to offsets in the file.  Each
.I map
comprises one or more
.BR 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.
.PP
.I Crackhdr
interprets the header of the executable
associated with
the open file descriptor
.IR fd .
It loads the data structure
.I fp
with a machine-independent description
of the header information and
points global variable
.I mach
to the
.B Mach
data structure containing processor-dependent parameters
of the target architecture.
.PP
.I Machbytype
selects architecture-specific data structures and parameter
values based on
the code stored in the
field named
.I type
in the
.B Fhdr
data structure.
.I Machbyname
performs the same selection based
on the name of a processor class; see
.IR 2c (1)
for a list of valid names.
Both functions point global variables
.I mach
and
.I machdata
to the
.I Mach
and
.I Machdata
data structures appropriate for the
target architecture and load global variable
.I asstype
with the proper disassembler type code.
.PP
.I Newmap
creates an empty map with
.I n
segments.
If
.I 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.
.PP
.I Setmap
loads the first unused segment in
.I map
with the
segment mapping parameters.
.I Fd
is an open file descriptor associated with
an executable.
.I Base
and
.I end
contain the lowest and highest virtual addresses
mapped by the segment.
.I Foffset
is the offset to the start of the segment in the file.
.I Name
is a name to be attached to the segment.
.PP
.I Findseg
returns the index of the the
segment named
.I name
in
.IR map .
A return of -1 indicates that no
segment matches
.IR name .
.PP
.I Unusemap
marks segment number
.I seg
in map
.I map
unused.  Other
segments in the map remain unaffected.
.PP
.I Loadmap
initializes a default map containing
segments named `text' and `data' that
map the instruction and data segments
of the executable described in the
.B Fhdr
structure pointed to by
.IR fp .
Usually that structure was loaded by
.IR crackhdr
and can be passed to this function without
modification.
If
.I map
is non-zero, that map, which must have been
dynamically allocated, is resized to contain two segments;
otherwise a new map is allocated.
This function returns zero if allocation fails.
.I Loadmap
is usually used to build a map for accessing
a static executable, for example, an executable
program file.
.PP
.I Attachproc
constructs a map for accessing a
running process.  It
returns the address of a
.I Map
containing segments mapping the
address space of the running process
whose process ID is
.BR pid .
If
.B kflag
is non-zero, the process is assumed to be
a kernel process.
.B Corefd
is an file descriptor opened to
.BR /proc/\fIpid\fP/mem .
.B Fp
points to the
.I Fhdr
structure describing the header
of the executable.  For most architectures
the resulting
.I 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
.B 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.
.I Attachproc
returns zero if it is unable to build the map
for the specified process.
.PP
.IR Get1 ,
.IR get2 ,
.IR get4 ,
and
.I get8
retrieve the data stored at address
.I addr
in the executable associated
with
.IR map .
.I Get1
retrieves
.I n
bytes of data beginning at
.I addr
into
.IR buf .
.IR Get2 ,
.I get4
and
.I get8
retrieve 16-bit, 32-bit and 64-bit values respectively,
into the location pointed to by
.IR 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
.IR get2 ,
.IR get4 ,
and
.I get8
may not be the same as the byte sequences
returned by
.I get1
when
.I 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 
.I map
is negative, the address itself is placed in the
return location.  These functions return the number
of bytes read or a \-1 when there is an error.
.PP
.IR Put1 ,
.IR put2 ,
.IR put4 ,
and
.I put8
write to
the executable associated with
.IR map .
The address is translated using the
map parameters and multi-byte quantities are
byte-swapped, if necessary, before they are written.
.I Put1
transfers
.I n
bytes stored at
.IR buf ;
.IR put2 ,
.IR put4 ,
and
.I put8
write the 16-bit, 32-bit or 64-bit quantity contained in
.IR val ,
respectively.  The number of bytes transferred is returned.
A \-1 return value indicates an error.
.PP
.IR Beswab ,
.IR beswal ,
and
.I beswav
return the
.BR ushort ,
.BR long ,
and
.B vlong
big-endian representation of
.IR val ,
respectively.
.IR Leswab ,
.IR leswal ,
and
.I leswav
return the little-endian representation of the
.BR ushort ,
.BR long ,
and
.B vlong
contained in
.IR val .
.SH SOURCE
.B /sys/src/libmach
.SH "SEE ALSO"
.IR 2c (1),
.IR symbol (2),
.IR object (2),
.IR errstr (2),
.IR proc (3),
.IR a.out (6)
.SH DIAGNOSTICS
These routines set
.IR errstr .