NAME compel - Execute parasitic code within another process.

SYNOPSIS

       compel hgen [option ...]

       compel plugins [PLUGIN_NAME ...]

       compel [--compat] includes | cflags | ldflags

       compel [--compat] [--static] libs

DESCRIPTION

       compel  is  a  utility  to execute arbitrary code, also called parasite code, in the context of a foreign
       process. The parasitic code, once compiled with compel flags and packed, can be executed in  the  context
       of  other  tasks.  Currently  there  is  only  one  way to load the parasitic blob into victim task using
       libcompel.a, called c-header.

ARGUMENTS

   Positional Arguments

       hgen
           create a header from the .po file, which is the parasite binary.

       plugins
           prints the plugins available.

       ldflags
           prints the ldflags available to compel during linking of parasite code.

       cflags
           prints the compel cflags to be used during compilation of parasitic code.

       includes
           prints list of standard include directories.

       libs
           prints list of static or dynamic libraries that compel can link with.

OPTIONS

       -f, --file FILE
           Path to the binary file, FILE, which compel must turn into a header

       -o, --output FILE
           Path to the header file, FILE, where compel must write the resulting header.

       -p, --prefix NAME
           Specify prefix for var names

       -l, --log-level NUM
           Default log level of compel.

       -h, --help
           Prints usage and exits.

       -V, --version
           Prints version number of compel.

SOURCE EXAMPLES

   Parasitic Code

       #include <compel/plugins/std.h>

       int parasite_trap_cmd(int cmd, void *args); //gets called by compel_run_in_thread()

       int   parasite_daemon_cmd(int   cmd,   void   *arg);   //   gets   called   by   compel_rpc_call()    and
       compel_rpc_call_sync()

       void parasite_cleanup(void); //gets called on parasite unload by compel_cure()

   Infecting code

       The parasitic code is compiled and converted to a header using compel, and included here.

       #include <compel/infect.h>

       #include "parasite.h"

       Following steps are performed to infect the victim process:

       •   stop the task: int compel_stop_task(int pid);

       •   prepare infection handler: struct parasite_ctl *compel_prepare(int pid);

       •   execute system call: int compel_syscall(ctl, int syscall_nr, long *ret, int arg ...);

       •   infect victim: int compel_infect(ctl, nr_thread, size_of_args_area);

       •   cure the victim: int compel_cure(ctl); //ctl pointer is freed by this call

       •   Resume  victim:  int  compel_resume_task(pid,  orig_state,  state) or int compel_resume_task_sig(pid,
           orig_state, state, stop_signo).  //compel_resume_task_sig() could be used in case when victim  is  in
           stopped state. stop_signo could be read by calling compel_parse_stop_signo().

       ctl  must  be  configured  with  blob  information  by  calling  PREFIX_setup_c_header(), with ctl as its
       argument. PREFIX is the argument given to -p when calling hgen, else it is deduced from file name.

EXAMPLES

       To generate a header file(.h) from a parasite binary file(.po) use:

               compel hgen -f parasite.po -o parasite.h

       parasite.po file is obtained by compiling the parasite source with compel flags and linking it  with  the
       compel plugins.

AUTHOR

       The CRIU team.

criu 4.0                                           03/10/2025                                          COMPEL(1)