[pso] Surse glibc sub LXR

[Octavian Voicu]

2009/5/27 Bogdan Tenea <tenea.bogdan at gmail.com>

> Am si eu intrebare legata de glibc. Vroiam sa fac o prezentare maine cu
> titlu "De la sendto la fir", am luat sursele glibc, am gasit sendto la
> http://koala.cs.pub.ro/lxr/glibc/sysdeps/mach/hurd/sendto.c si am gasit ca
> in spate apeleaza un __socket_send catre care nu mai gasesc referinte nici
> macar ca freetext. Unde gresesc?
>

Functia este generata de fisierul
sendto.S<http://koala.cs.pub.ro/lxr/glibc/sysdeps/unix/sysv/linux/sendto.S>,
intr-un mod mai indirect:

#define socket  sendto
/* ... */
#include <socket.S>

In socket.S<http://koala.cs.pub.ro/lxr/glibc/sysdeps/unix/sysv/linux/i386/socket.S>se
implementeaza functia apeland syscall-ul socketcall cu argumentul
SOCKOP_sendto<http://koala.cs.pub.ro/lxr/glibc/sysdeps/unix/sysv/linux/socketcall.h#L39>
.
In codul de mai jos (vezi socket.S) `socket' are valoarea definita mai sus:

movl $SYS_ify(socketcall), %eax /* System call number in %eax.  */

/* Use ## so `socket' is a separate token that might be #define'd.  */
movl $P(SOCKOP_,socket), %ebx   /* Subcode is first arg to syscall.  */
lea 4(%esp), %ecx               /* Address of args is 2nd arg.  */

/* Do the system call trap.  */
ENTER_KERNEL

Toate chestiile astea sunt doar detalii de implementare, raspunsul scurt e
ca se apeleaza syscall-ul
socketcall<http://lxr.linux.no/linux+v2.6.29/net/socket.c#L2049>care e
de fapt un mare switch care face dispatch la functia corespunzatoare
codului primit, adica
sendto<http://lxr.linux.no/linux+v2.6.29/net/socket.c#L1618>(care e de
fapt un alt syscall, probabil in alte implementari se apeleaza
acest syscall direct).



-- 
Octavian Voicu
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