OSDC 2007
A Humbling Language
Rusty Russell

Time Better Spent
tcmalloc
●
http://goog-perftools.sourceforge.net/doc/tcmalloc.html
–
tdb
●
– ftp://ftp.samba.org/pub/unpacked/tdb
lguest
●
http://lguest.ozlabs.org
–

ABCDEFG
HIJKLM
NOPQRST
UVWXYZ

BCD G
LM
NOP RS
UVW Z

C
LM
NO S
VW Z

C
O S

C
O S

C
S

C
S

C

C

C

C: A Historic Language

http://www.thorstenkoerner.de/uploads/thompson_ritchie.jpg

+=
register
entry

foo.c

foo.c
preprocessor

foo.c
#define FOO 17
preprocessor

foo.c
#define FOO(x) (17*(x))
preprocessor

foo.c
#ifdef LINUX
...
#else
preprocessor
...
#endif

foo.c
#include \"foo.h\"
preprocessor

foo.c
#include \"foo.h\"
foo.h
preprocessor

foo.c
#include \"foo.h\"
foo.h
preprocessor
#include <stdio.h>

foo.c
#include \"foo.h\"
foo.h
preprocessor
#include <stdio.h>
stdio.h

foo.c
#include \"foo.h\"
foo.h
preprocessor
#include <stdio.h>
stdio.h
# include <features.h>
# include <stddef.h>
# include <bits/types.h>
#include <libio.h>
# include <stdarg.h>
#include <bits/stdio_lim.h>
#include <bits/sys_errlist.h>
# include <getopt.h>
# include <bits/stdio.h>
# include <bits/stdio2.h>
# include <bits/stdio-ldbl.h>

foo.c
preprocessor

foo.c
preprocessor

foo.c
preprocessor
foo.i

foo.c
preprocessor
compiler

foo.c
preprocessor
compiler

foo.c
preprocessor
compiler
foo.s

foo.c
preprocessor
compiler
assembler

foo.c bar.c baz.c
preprocessor
compiler
assembler

foo.c bar.c baz.c
preprocessor
compiler
assembler
linker

foo.c bar.c baz.c
preprocessor
compiler
assembler
linker
foobarbaz

foo.c bar.c baz.c
make
preprocessor
compiler
assembler
linker
foobarbaz

foo.c bar.c baz.c
make
preprocessor
compiler
ccache
assembler
linker
foobarbaz

foo.c bar.c baz.c
make
preprocessor
compiler
ccache
distcc
assembler
linker
foobarbaz

foo.c bar.c baz.c
make
preprocessor
ccontrol
compiler
ccache
distcc
assembler
linker
foobarbaz

foo.c bar.c baz.c
make gcc *.c
preprocessor
ccontrol
compiler
ccache
distcc
assembler
linker
foobarbaz

1988

entry
void
const
volatile
enum
function prototypes

1999

inline

foo.c bar.c baz.c
preprocessor
int
compiler foo(int x)...
assembler
linker
foobarbaz

foo.c bar.c baz.c
preprocessor
int
compiler foo(int x)...
assembler
linker
foobarbaz

foo.c bar.c baz.c
preprocessor foo.h
compiler
assembler
linker
foobarbaz

foo.c bar.c baz.c
preprocessor foo.h
inline int
foo(int x)...
compiler
assembler
linker
foobarbaz

WTF?

WTF?
This isn't a
scripting
language!

Images from Wikipedia

C

C
C

C
C
CC

C
ontrol

C
ycles

C
ore

C
ache

“Sell Me a C!”

The Magic

The Magic

struct list_head
{
struct list_head *next, *prev;
};

struct list_head
{
struct list_head *next, *prev;
};
struct thing
{
struct list_head elem;
...
};

void *kmalloc(size_t size,
gfp_t flags);

Just a little magic?

long f(struct foo *a, struct foo *b)
{
return b – a;
}

Magic to get closer to the machine...

struct elems
{
unsigned int num_elems;
struct elem[0];
};

#define memcpy(t, f, n) \\
(__builtin_constant_p(n) ? \\
__constant_memcpy((t),(f),(n)) : \\
__memcpy((t),(f),(n)))

Magic to strengthen language features...

DANGER!
Magic to strengthen language features...

#define new(type) \\
((type *)malloc(sizeof(type))

#define min(x,y) ({ \\
typeof(x) _x = (x); \\
typeof(y) _y = (y); \\
(void) (&_x == &_y); \\
_x < _y ? _x : _y; })

_Bool

#include <stdbool.h>

#include <stdbool.h>
#define bool _Bool

#define begin {
#define end }

talloc(context, type)

valgrind

C