Android 系统调用

http://www.eoeandroid.com/thread-4668-1-1.html

http://blog.chinaunix.net/uid-9078996-id-2010323.html

http://blog.csdn.net/andyhuabing/article/details/7183369

1、Syscall stub：

每个系统调用函数都由一个小的汇编代码段实现(称为”syscall stub”),这是由tools/gensyscalls.py工具自动生成的，它从SYSCALL.TXT中取得输入参数。
SYSCALLS.TXT包含了一份要生成的系统调用块列表，和相应的系统调用数字标识符（ARM和X86不一样），以及它的签署。
如果你要修改这个文件，你可能要使用tools/checksyscalls.py工具，检查它里面是否包含官方linux核心头文件，如果有不合法的syscall ids，它会报告错误。
有时，C库函数其实就是一个包装，它内部调用相应的syscall名称，例如，exit函数由C库提供，它调用了_exit()这个syscall stub.
详细内容请参考SYSCALLS.TXT文件。

2、比如要增加消息队列的函数：
(1). 修改 SYSCALL.TXT
增加：
long ipc(unsigned int call, int first, unsigned long second, unsigned long third, void __user *ptr, long fifth) 117
(2). 执行 tools/gensyscalls.py
(3). 以下内容会由 tools/gensyscalls.py 自动产生：

bionic/libc/arch-mips/syscalls.mk
----------------------------------------------------------------------------------------------------------------------------
syscall_src += arch-mips/syscalls/ipc.S
----------------------------------------------------------------------------------------------------------------------------

bionic/libc/include/sys/linux-syscalls.h
----------------------------------------------------------------------------------------------------------------------------
#define _NR_ipc (_NR_SYSCALL_BASE + 117)
----------------------------------------------------------------------------------------------------------------------------

bionic/libc/include/sys/linux-unistd.h
----------------------------------------------------------------------------------------------------------------------------
int ipc (unsigned int call, int first, int second, int third, void* ptr, long fifth);
----------------------------------------------------------------------------------------------------------------------------

(4). 手动编写
bionic/libc/Android.mk
----------------------------------------------------------------------------------------------------------------------------
ifeq ($(TARGET_ARCH),mips)
libc_common_src_files += \
arch-mips/bionic/sys_ipc.c \

----------------------------------------------------------------------------------------------------------------------------
bionic/libc/arch-mips/bionic/sys_ipc.c
----------------------------------------------------------------------------------------------------------------------------

#include <stdarg.h>#include <sys/msg.h>extern int ipc (unsigned int call, int first, int second, int third, void* ptr, long fifth);int semget (key_t  key, int  nsems, int  semflg){    return ipc(SEMGET, key, nsems, semflg, (void*)NULL, (long)NULL);}int semop (int  semid, struct sembuf*  sops, size_t  nsops){    return ipc(SEMOP, semid, (int)nsops, 0, sops, (long)NULL);}void* shmat (int  shmid, const void*  shmaddr, int  shmflg){    int rval;    unsigned long raddr;    rval = ipc(SHMAT, shmid, shmflg, (int)&raddr, (void*)shmaddr, (long)NULL);    if (rval < 0)        return (char *)rval;    return (char *)raddr;}int shmctl (int  shmid, int  cmd, struct shmid_ds*  buf){    return ipc(SHMCTL, shmid, cmd, 0, buf, (long)NULL);}int shmget (key_t  key, size_t  size, int  shmflg){    return ipc(SHMGET, key, size, shmflg, (void*)NULL, (long)NULL);}int msgctl (int  msqid, int  cmd, struct msqid_ds *buf){    return ipc(MSGCTL, msqid, cmd, 0, buf, (long)NULL);}int shmdt (const void*  shmaddr){    return ipc(SHMDT, 0, 0, 0, (void*)shmaddr, (long)NULL);}int msgget (key_t  key, int  msgflg){    return ipc(MSGGET, key, msgflg, 0, NULL, (long)NULL);}ssize_t msgrcv (int msqid, void *msgp, size_t msgsz, long int msgtyp, int msgflg){    struct ipc_kludge tmp;    tmp.msgp = msgp;    tmp.msgtyp = msgtyp;    return ipc(MSGRCV, msqid, msgsz, msgflg, &tmp, (long)NULL);}int msgsnd (int  msqid, const void* msgp, size_t  msgsz, int  msgflg){    return ipc(MSGSND, msqid, msgsz, msgflg, (void*)msgp, (long)NULL);}

bionic/libc/arch-mips/syscalls/ipc.S
----------------------------------------------------------------------------------------------------------------------------
/* autogenerated by gensyscalls.py */
#include <sys/linux-syscalls.h>
.text
.globl ipc
.align 4
.ent ipc

ipc:
.set noreorder
.cpload $t9
li $v0, __NR_ipc
syscall
bnez $a3, 1f
move $a0, $v0
j $ra
nop
1:
la $t9,__set_errno
j $t9
nop
.set reorder
.end ipc

----------------------------------------------------------------------------------------------------------------------------
bionic/libc/include/sys/msg.h
----------------------------------------------------------------------------------------------------------------------------

#ifndef _SYS_MSG_H#define _SYS_MSG_H#include <features.h>#define __need_size_t#include <stddef.h>/* Get common definition of System V style IPC.  */#include <sys/ipc.h>/* Get system dependent definition of `struct msqid_ds' and more.  */#include <msq.h>/* Define types required by the standard.  */#define    __need_time_t#include <time.h>#ifndef __pid_t_definedtypedef __pid_t pid_t;# define __pid_t_defined#endif#ifndef __ssize_t_definedtypedef __ssize_t ssize_t;# define __ssize_t_defined#endif#define SEMOP         1#define SEMGET         2#define SEMCTL         3#define SEMTIMEDOP     4#define MSGSND        11#define MSGRCV        12#define MSGGET        13#define MSGCTL        14#define SHMAT        21#define SHMDT        22#define SHMGET        23#define SHMCTL        24/* The following System V style IPC functions implement a message queue   system.  The definition is found in XPG2.  */#ifdef __USE_GNU/* Template for struct to be used as argument for `msgsnd' and `msgrcv'.  */struct msgbuf  {    long int mtype;        /* type of received/sent message */    char mtext[1];        /* text of the message */  };#endifstruct ipc_kludge {    struct msgbuf __user *msgp;    long msgtyp;};__BEGIN_DECLS/* Message queue control operation.  */extern int msgctl (int __msqid, int __cmd, struct msqid_ds *__buf) ;/* Get messages queue.  */extern int msgget (key_t __key, int __msgflg) ;/* Receive message from message queue.   This function is a cancellation point and therefore not marked with   __THROW.  */extern ssize_t msgrcv (int __msqid, void *__msgp, size_t __msgsz, long int __msgtyp, int __msgflg);/* Send message to message queue.   This function is a cancellation point and therefore not marked with   __THROW.  */extern int msgsnd (int __msqid, __const void *__msgp, size_t __msgsz,   int __msgflg);__END_DECLS#endif /* sys/msg.h */

----------------------------------------------------------------------------------------------------------------------------
Create bionic/libc/include/msq.h

#ifndef _SYS_MSG_H#error "Never use <msq.h> directly; include <sys/msg.h> instead." #endif#include <sys/types.h>/* Define options for message queue functions.  */#define MSG_NOERROR     010000  /* no error if message is too big *//* Types used in the structure definition.  */typedef unsigned short int msgqnum_t;typedef unsigned short int msglen_t;/* Structure of record for one message inside the kernel.   The type `struct __msg' is opaque.  */struct msqid_ds{  struct ipc_perm msg_perm;     /* structure describing operation permission */  __time_t msg_stime;           /* time of last msgsnd command */  __time_t msg_rtime;           /* time of last msgrcv command */  __time_t msg_ctime;           /* time of last change */  msgqnum_t msg_qnum;           /* number of messages currently on queue */  msglen_t msg_qbytes;          /* max number of bytes allowed on queue */  __pid_t msg_lspid;            /* pid of last msgsnd() */  __pid_t msg_lrpid;            /* pid of last msgrcv() */};

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