<s>
In	O
computing	O
,	O
executable	B-Application
code	I-Application
,	O
an	O
executable	B-Application
file	I-Application
,	O
or	O
an	O
executable	B-Application
program	I-Application
,	O
sometimes	O
simply	O
referred	O
to	O
as	O
an	O
executable	B-Application
or	O
binary	O
,	O
causes	O
a	O
computer	O
"	O
to	O
perform	O
indicated	O
tasks	O
according	O
to	O
encoded	O
instructions	O
"	O
,	O
as	O
opposed	O
to	O
a	O
that	O
must	O
be	O
interpreted	O
(	O
parsed	B-Language
)	O
by	O
a	O
program	O
to	O
be	O
meaningful	O
.	O
</s>
<s>
"	O
Instructions	O
"	O
is	O
traditionally	O
taken	O
to	O
mean	O
machine	B-Language
code	I-Language
instructions	O
for	O
a	O
physical	O
CPU	B-General_Concept
.	O
</s>
<s>
In	O
some	O
contexts	O
,	O
a	O
file	O
containing	O
scripting	O
instructions	O
(	O
such	O
as	O
bytecode	O
)	O
may	O
also	O
be	O
considered	O
executable	B-Application
.	O
</s>
<s>
Executable	B-Application
files	I-Application
can	O
be	O
hand-coded	O
in	O
machine	B-Language
language	I-Language
,	O
although	O
it	O
is	O
far	O
more	O
convenient	O
to	O
develop	O
software	O
as	O
source	O
code	O
in	O
a	O
high-level	B-Language
language	I-Language
that	O
can	O
be	O
easily	O
understood	O
by	O
humans	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
source	O
code	O
might	O
be	O
specified	O
in	O
assembly	B-Language
language	I-Language
instead	O
,	O
which	O
remains	O
human-readable	O
while	O
being	O
closely	O
associated	O
with	O
machine	B-Language
code	I-Language
instructions	O
.	O
</s>
<s>
The	O
high-level	B-Language
language	I-Language
is	O
compiled	B-Language
into	O
either	O
an	O
executable	B-Application
machine	B-Language
code	I-Language
file	O
or	O
a	O
non-executable	O
machine	B-Language
code	I-Language
–	O
object	B-Application
file	I-Application
of	O
some	O
sort	O
;	O
the	O
equivalent	O
process	O
on	O
assembly	B-Language
language	I-Language
source	O
code	O
is	O
called	O
assembly	O
.	O
</s>
<s>
Several	O
object	B-Application
files	I-Application
are	O
linked	B-Application
to	O
create	O
the	O
executable	B-Application
.	O
</s>
<s>
Object	B-Application
files	I-Application
--	O
executable	B-Application
or	O
not	O
--	O
are	O
typically	O
stored	O
in	O
a	O
container	O
format	O
,	O
such	O
as	O
Executable	B-Application
and	O
Linkable	O
Format	O
(	O
ELF	O
)	O
or	O
Portable	O
Executable	B-Application
(	O
PE	O
)	O
which	O
is	O
operating	O
system-specific	O
.	O
</s>
<s>
This	O
gives	O
structure	O
to	O
the	O
generated	O
machine	B-Language
code	I-Language
,	O
for	O
example	O
dividing	O
it	O
into	O
sections	O
such	O
as	O
.text	B-General_Concept
(	O
executable	B-Application
code	I-Application
)	O
,	O
.data	B-General_Concept
(	O
initialized	O
global	O
and	O
static	O
variables	O
)	O
,	O
and	O
.rodata	B-General_Concept
(	O
read-only	O
data	O
,	O
such	O
as	O
constants	O
and	O
strings	O
)	O
.	O
</s>
<s>
Executable	B-Application
files	I-Application
typically	O
also	O
include	O
a	O
runtime	B-Device
system	I-Device
,	O
which	O
implements	O
runtime	O
language	O
features	O
(	O
such	O
as	O
task	O
scheduling	O
,	O
exception	B-General_Concept
handling	I-General_Concept
,	O
calling	O
static	O
constructors	O
and	O
destructors	O
,	O
etc	O
.	O
)	O
</s>
<s>
and	O
interactions	O
with	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
notably	O
passing	O
arguments	O
,	O
environment	O
,	O
and	O
returning	O
an	O
exit	B-Operating_System
status	I-Operating_System
,	O
together	O
with	O
other	O
startup	O
and	O
shutdown	O
features	O
such	O
as	O
releasing	O
resources	O
like	O
file	B-Application
handles	I-Application
.	O
</s>
<s>
For	O
C	O
,	O
this	O
is	O
done	O
by	O
linking	B-Application
in	O
the	O
crt0	B-Language
object	O
,	O
which	O
contains	O
the	O
actual	O
entry	B-Language
point	I-Language
and	O
does	O
setup	O
and	O
shutdown	O
by	O
calling	O
the	O
runtime	B-Library
library	I-Library
.	O
</s>
<s>
Executable	B-Application
files	I-Application
thus	O
normally	O
contain	O
significant	O
additional	O
machine	B-Language
code	I-Language
beyond	O
that	O
directly	O
generated	O
from	O
the	O
specific	O
source	O
code	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
it	O
is	O
desirable	O
to	O
omit	O
this	O
,	O
for	O
example	O
for	O
embedded	O
systems	O
development	O
,	O
or	O
simply	O
to	O
understand	O
how	O
compilation	B-Language
,	O
linking	B-Application
,	O
and	O
loading	O
work	O
.	O
</s>
<s>
In	O
C	O
,	O
this	O
can	O
be	O
done	O
by	O
omitting	O
the	O
usual	O
runtime	O
,	O
and	O
instead	O
explicitly	O
specifying	O
a	O
linker	B-Application
script	I-Application
,	O
which	O
generates	O
the	O
entry	B-Language
point	I-Language
and	O
handles	O
startup	O
and	O
shutdown	O
,	O
such	O
as	O
calling	O
main	O
to	O
start	O
and	O
returning	O
exit	B-Operating_System
status	I-Operating_System
to	O
the	O
kernel	O
at	O
the	O
end	O
.	O
</s>
<s>
In	O
order	O
to	O
be	O
executed	O
by	O
the	O
system	O
(	O
such	O
as	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
,	O
or	O
boot	B-Application
loader	I-Application
)	O
,	O
an	O
executable	B-Application
file	I-Application
must	O
conform	O
to	O
the	O
system	O
's	O
application	B-Operating_System
binary	I-Operating_System
interface	I-Operating_System
(	O
ABI	O
)	O
.	O
</s>
<s>
In	O
simple	O
interfaces	O
,	O
a	O
file	O
is	O
executed	O
by	O
loading	O
it	O
into	O
memory	O
and	O
jumping	O
to	O
the	O
start	O
of	O
the	O
address	B-General_Concept
space	O
and	O
executing	O
from	O
there	O
.	O
</s>
<s>
In	O
more	O
complicated	O
interfaces	O
,	O
executable	B-Application
files	I-Application
have	O
additional	O
metadata	O
specifying	O
a	O
separate	O
entry	B-Language
point	I-Language
.	O
</s>
<s>
For	O
example	O
,	O
in	O
ELF	O
,	O
the	O
entry	B-Language
point	I-Language
is	O
defined	O
in	O
the	O
header	O
's	O
e_entry	O
field	O
,	O
which	O
specifies	O
the	O
(	O
virtual	O
)	O
memory	O
address	B-General_Concept
at	O
which	O
to	O
start	O
execution	O
.	O
</s>
<s>
In	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
,	O
this	O
field	O
is	O
set	O
by	O
the	O
linker	B-Application
based	O
on	O
the	O
_start	O
symbol	O
.	O
</s>
