'\" t
.\"     Title: compel
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 08/05/2023
.\"    Manual: CRIU Manual
.\"    Source: criu 3.17.1
.\"  Language: English
.\"
.TH "COMPEL" "1" "08/05/2023" "criu 3\&.17\&.1" "CRIU Manual"
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..
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.\" -----------------------------------------------------------------
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.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "Name"
compel \- Execute parasitic code within another process\&.
.SH "Synopsis"
.sp
\fBcompel\fR \fIhgen\fR [\fIoption\fR \&...]
.sp
\fBcompel\fR \fIplugins\fR [\fIPLUGIN_NAME\fR \&...]
.sp
\fBcompel\fR [\fI\-\-compat\fR] \fIincludes\fR | \fIcflags\fR | \fIldflags\fR
.sp
\fBcompel\fR [\fI\-\-compat\fR] [\fI\-\-static\fR] \fIlibs\fR
.SH "DESCRIPTION"
.sp
\fBcompel\fR 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\&.
.SH "ARGUMENTS"
.SS "Positional Arguments"
.PP
\fBhgen\fR
.RS 4
create a header from the \&.po file, which is the parasite binary\&.
.RE
.PP
\fBplugins\fR
.RS 4
prints the plugins available\&.
.RE
.PP
\fBldflags\fR
.RS 4
prints the ldflags available to compel during linking of parasite code\&.
.RE
.PP
\fBcflags\fR
.RS 4
prints the compel cflags to be used during compilation of parasitic code\&.
.RE
.PP
\fBincludes\fR
.RS 4
prints list of standard include directories\&.
.RE
.PP
\fBlibs\fR
.RS 4
prints list of static or dynamic libraries that compel can link with\&.
.RE
.SH "OPTIONS"
.PP
\fB\-f\fR, \fB\-\-file\fR \fIFILE\fR
.RS 4
Path to the binary file,
\fIFILE\fR, which
\fBcompel\fR
must turn into a header
.RE
.PP
\fB\-o\fR, \fB\-\-output\fR \fIFILE\fR
.RS 4
Path to the header file,
\fIFILE\fR, where compel must write the resulting header\&.
.RE
.PP
\fB\-p\fR, \fB\-\-prefix\fR \fINAME\fR
.RS 4
Specify prefix for var names
.RE
.PP
\fB\-l\fR, \fB\-\-log\-level\fR \fINUM\fR
.RS 4
Default log level of compel\&.
.RE
.PP
\fB\-h\fR, \fB\-\-help\fR
.RS 4
Prints usage and exits\&.
.RE
.PP
\fB\-V\fR, \fB\-\-version\fR
.RS 4
Prints version number of compel\&.
.RE
.SH "SOURCE EXAMPLES"
.SS "Parasitic Code"
.sp
\fB#include <compel/plugins/std\&.h>\fR
.sp
\fBint parasite_trap_cmd(int cmd, void *args);\fR //gets called by compel_run_in_thread()
.sp
\fBint parasite_daemon_cmd(int cmd, void *arg);\fR // gets called by compel_rpc_call() and compel_rpc_call_sync()
.sp
\fBvoid parasite_cleanup(void);\fR //gets called on parasite unload by compel_cure()
.SS "Infecting code"
.sp
The parasitic code is compiled and converted to a header using \fBcompel\fR, and included here\&.
.sp
\fB#include <compel/infect\&.h>\fR
.sp
\fB#include "parasite\&.h"\fR
.sp
Following steps are performed to infect the victim process:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
stop the task:
\fBint compel_stop_task(int pid);\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
prepare infection handler:
\fBstruct parasite_ctl *compel_prepare(int pid);\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
execute system call:
\fBint compel_syscall(ctl, int syscall_nr, long *ret, int arg \&...);\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
infect victim:
\fBint compel_infect(ctl, nr_thread, size_of_args_area);\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
cure the victim:
\fBint compel_cure(ctl);\fR
//ctl pointer is freed by this call
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Resume victim:
\fBint compel_resume_task(pid, orig_state, state);\fR
.RE
.sp
\fBctl\fR must be configured with blob information by calling \fBPREFIX_setup_c_header()\fR, with ctl as its argument\&. \fBPREFIX\fR is the argument given to \fB\-p\fR when calling hgen, else it is deduced from file name\&.
.SH "EXAMPLES"
.sp
To generate a header file(\&.h) from a parasite binary file(\&.po) use:
.sp
.if n \{\
.RS 4
.\}
.fam C
.ps -1
.nf
.BB lightgray
    compel hgen \-f parasite\&.po \-o parasite\&.h
.EB lightgray
.fi
.fam
.ps +1
.if n \{\
.RE
.\}
.sp
\fIparasite\&.po\fR file is obtained by compiling the parasite source with compel flags and linking it with the compel plugins\&.
.SH "AUTHOR"
.sp
The CRIU team\&.