term% cat index.txt EXEC(2) System Calls Manual EXEC(2)
NAME
exec, execl, _privates, _nprivates, _tos - execute a file
SYNOPSIS
#include <u.h>
#include <libc.h>
void* exec(char *name, char* argv[])
void* execl(char *name, ...)
void **_privates;
int _nprivates;
#include <tos.h>
typedef struct Tos Tos;
struct Tos {
struct { ... } prof; /* profiling data */
uvlong cyclefreq; /* cycle clock frequency */
vlong kcycles; /* kernel cycles */
vlong pcycles; /* process cycles (kernel + user) */
ulong pid; /* process id */
ulong clock; /* profiling clock */
/* top of stack is here */
};
extern Tos *_tos;
DESCRIPTION
Exec and execl overlay the calling process with the named file, then
transfer to the entry point of the image of the file.
Name points to the name of the file to be executed; it must not be a
directory, and the permissions must allow the current user to execute
it (see stat(2)). It should also be a valid binary image, as defined
in the a.out(6) for the current machine architecture, or a shell script
(see rc(1)). The first line of a shell script must begin with followed
by the name of the program to interpret the file and any initial argu‐
ments to that program, for example
#!/bin/rc
ls | mc
When a C program is executed, it is called as follows:
void main(int argc, char *argv[])
Argv is a copy of the array of argument pointers passed to exec; that
array must end in a null pointer, and argc is the number of elements
before the null pointer. By convention, the first argument should be
the name of the program to be executed. Execl is like exec except that
argv will be an array of the parameters that follow name in the call.
The last argument to execl must be a null pointer.
For a file beginning #!, the arguments passed to the program (/bin/rc
in the example above) will be the name of the file being executed, any
arguments on the #! line, the name of the file again, and finally the
second and subsequent arguments given to the original exec call. The
result honors the two conventions of a program accepting as argument a
file to be interpreted and argv[0] naming the file being executed.
Most attributes of the calling process are carried into the result; in
particular, files remain open across exec (except those opened with
OCEXEC OR'd into the open mode; see open(2)); and the working directory
and environment (see env(3)) remain the same. However, a newly exec'ed
process has no notification handler (see notify(2)).
The global cell _privates points to an array of _nprivates elements of
per-process private data. This storage is private for each process,
even if the processes share data segments.
When the new program begins, the global pointer _tos is set to the ad‐
dress of a structure that holds information allowing accurate time
keeping and clock reading in user space. These data are updated by the
kernel during of the life of the process, including across rforks and
execs. If there is a user-space accessible fast clock (a processor cy‐
cle counter), cyclefreq will be set to its frequency in Hz. Kcycles
(pcycles) counts the number of cycles this process has spent in kernel
mode (kernel and user mode). Pid is the current process's id. Clock
is the user-profiling clock (see prof(1)). Its time is measured in
milliseconds but is updated at a system-dependent lower rate. This
clock is typically used by the profiler but is available to all pro‐
grams.
The above conventions apply to C programs; the raw system interface to
the new image is as follows: the word pointed to by the stack pointer
is argc; the words beyond that are the zeroth and subsequent elements
of argv, followed by a terminating null pointer; and the return regis‐
ter (e.g. R0 on the 68020) contains the address of the clock informa‐
tion.
SOURCE
/sys/src/libc/9syscall
/sys/src/libc/port/execl.c
SEE ALSO
prof(1), intro(2), stat(2)
DIAGNOSTICS
If these functions fail, they return and set errstr. There can be no
return to the calling process from a successful exec or execl; the
calling image is lost.
BUGS
There is a large but finite limit on the size of an argment list, typi‐
cally around 409,600 bytes. The kernel constant TSTKSIZ controls this.
EXEC(2)