ref: a8d00e5d56b261376410c3c87c46327362763bd8
dir: /sys/man/2/exec/
.TH EXEC 2 .SH NAME exec, execl, _privates, _nprivates, _tos \- execute a file .SH SYNOPSIS .B #include <u.h> .br .B #include <libc.h> .PP .nf .B int exec(char *name, char* argv[]) .PP .B int execl(char *name, ...) .PP .B void **_privates; .PP .B int _nprivates; .PP .B #include <tos.h> .PP .ft L 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 */ }; .PP .B extern Tos *_tos; .fi .SH DESCRIPTION .I Exec and .I execl overlay the calling process with the named file, then transfer to the entry point of the image of the file. .PP .I 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 .IR stat (2)). It should also be a valid binary image, as defined in the .IR a.out (6) for the current machine architecture, or a shell script (see .IR rc (1)). The first line of a shell script must begin with .L #! followed by the name of the program to interpret the file and any initial arguments to that program, for example .IP .EX #!/bin/rc ls | mc .EE .PP When a C program is executed, it is called as follows: .IP .EX void main(int argc, char *argv[]) .EE .PP .I Argv is a copy of the array of argument pointers passed to .IR exec ; that array must end in a null pointer, and .I 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. .I Execl is like .I exec except that .I argv will be an array of the parameters that follow .I name in the call. The last argument to .I execl must be a null pointer. .PP For a file beginning .BR #! , the arguments passed to the program .RB ( /bin/rc in the example above) will be the name of the file being executed, any arguments on the .B #! line, the name of the file again, and finally the second and subsequent arguments given to the original .I exec call. The result honors the two conventions of a program accepting as argument a file to be interpreted and .B argv[0] naming the file being executed. .PP Most attributes of the calling process are carried into the result; in particular, files remain open across .I exec (except those opened with .B OCEXEC OR'd into the open mode; see .IR open (2)); and the working directory and environment (see .IR env (3)) remain the same. However, a newly .I exec'ed process has no notification handler (see .IR notify (2)). .PP The global cell .B _privates points to an array of .B _nprivates elements of per-process private data. This storage is private for each process, even if the processes share data segments. .PP When the new program begins, the global pointer .B _tos is set to the address 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 .IR rfork s and .IR exec s. If there is a user-space accessible fast clock (a processor cycle counter), .B cyclefreq will be set to its frequency in Hz. .B Kcycles .RB ( pcycles ) counts the number of cycles this process has spent in kernel mode (kernel and user mode). .B Pid is the current process's id. .B Clock is the user-profiling clock (see .IR 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 programs. .PP 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 .BR argc ; the words beyond that are the zeroth and subsequent elements of .BR argv , followed by a terminating null pointer; and the return register (e.g. .B R0 on the 68020) contains the address of the .B Tos structure. .SH SOURCE .B /sys/src/libc/9syscall .br .B /sys/src/libc/port/execl.c .SH SEE ALSO .IR prof (1), .IR intro (2), .IR stat (2) .SH DIAGNOSTICS If these functions fail, they return and set .IR errstr . There can be no return to the calling process from a successful .I exec or .IR execl ; the calling image is lost.