一、汇编语句sc不同平台的系统调用汇编不一样,powerpc平台通过汇编语句sc来执行系统调用
helloworld的例子(powerpc平台)
- /*
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/opt/montavista41/montavista/cge/devkit/ppc/85xx/bin/ppc_85xx-as -gstabs hello.s -o hello.o
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/opt/montavista41/montavista/cge/devkit/ppc/85xx/bin/ppc_85xx-ld hello.o -o hello
-
*/
-
.data # section declaration - variables only
-
-
msg:
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.string "Hello, world!\n"
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len = . - msg # length of our dear string
-
-
.text # section declaration - begin code
-
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.global _start
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_start:
-
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# write our string to stdout
-
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li 0,4 # syscall number (sys_write)
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li 3,1 # first argument: file descriptor (stdout)
- # second argument: pointer to message to write
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lis 4,msg@ha # load top 16 bits of &msg
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addi 4,4,msg@l # load bottom 16 bits
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li 5,len # third argument: message length
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sc # call kernel
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# and exit
-
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li 0,1 # syscall number (sys_exit)
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li 3,1 # first argument: exit code
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sc # call kernel
helloworld的例子(ia32平台)
- .data # section declaration
-
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msg:
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.string "Hello, world!\n"
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len = . - msg # length of our dear string
-
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.text # section declaration
-
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# we must export the entry point to the ELF linker or
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.global _start # loader. They conventionally recognize _start as their
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# entry point. Use ld -e foo to override the default.
-
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_start:
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# write our string to stdout
-
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movl $len,%edx # third argument: message length
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movl $msg,%ecx # second argument: pointer to message to write
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movl $1,%ebx # first argument: file handle (stdout)
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movl $4,%eax # system call number (sys_write)
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int $0x80 # call kernel
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# and exit
-
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movl $0,%ebx # first argument: exit code
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movl $1,%eax # system call number (sys_exit)
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int $0x80 # call kernel
二、系统调用过程系统调用本质上是一个中断向量
《中断相关知识(powerpc版)》 文件linux_2_6_24/arch/ppc/kernel/head_fsl_booke.S
- SET_IVOR(0, CriticalInput);
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SET_IVOR(1, MachineCheck);
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SET_IVOR(2, DataStorage);
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SET_IVOR(3, InstructionStorage);
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SET_IVOR(4, ExternalInput);
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SET_IVOR(5, Alignment);
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SET_IVOR(6, Program);
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SET_IVOR(7, FloatingPointUnavailable);
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SET_IVOR(8, SystemCall);
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SET_IVOR(9, AuxillaryProcessorUnavailable);
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SET_IVOR(10, Decrementer);
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SET_IVOR(11, FixedIntervalTimer);
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SET_IVOR(12, WatchdogTimer);
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SET_IVOR(13, DataTLBError);
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SET_IVOR(14, InstructionTLBError);
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SET_IVOR(15, Debug);
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SET_IVOR(32, SPEUnavailable);
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SET_IVOR(33, SPEFloatingPointData);
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SET_IVOR(34, SPEFloatingPointRound);
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#ifndef CONFIG_E200
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SET_IVOR(35, PerformanceMonitor);
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#endif
- 。。。。省略N多。。。。。
- /* System Call Interrupt */
START_EXCEPTION(SystemCall)
NORMAL_EXCEPTION_PROLOG
EXC_XFER_EE_LITE(0x0c00, DoSyscall)
使用汇编语句sc会产生一个SystemCall中断,接着根据中断向量中的地址去执行handler,即DoSyscall。
有关DoSyscall,它在文件arch/ppc/kernel/entry.S 中定义。
它根据sc执行时所用的系统调用编号来检索系统调用表,进行系统调用。
- _GLOBAL(DoSyscall)
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stw r3,ORIG_GPR3(r1)
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li r12,0
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stw r12,RESULT(r1)
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lwz r11,_CCR(r1) /* Clear SO bit in CR */
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rlwinm r11,r11,0,4,2
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stw r11,_CCR(r1)
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#ifdef SHOW_SYSCALLS
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bl do_show_syscall
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#endif /* SHOW_SYSCALLS */
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rlwinm r10,r1,0,0,(31-THREAD_SHIFT) /* current_thread_info() */
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lwz r11,TI_FLAGS(r10)
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andi. r11,r11,_TIF_SYSCALL_T_OR_A
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bne- syscall_dotrace
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syscall_dotrace_cont:
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cmplwi 0,r0,NR_syscalls
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lis r10,sys_call_table@h
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ori r10,r10,sys_call_table@l
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slwi r0,r0,2
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bge- 66f
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lwzx r10,r10,r0 /* Fetch system call handler [ptr] */
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mtlr r10
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addi r9,r1,STACK_FRAME_OVERHEAD
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PPC440EP_ERR42
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blrl /* Call handler */
系统调用表名为 sys_call_table,在 linux_2_6_24/arch/powerpc/kernel/systbl.S 中定义。
linux_2_6_24/include/asm-powerpc/systbl.h
系统调用表包含有实现每个系统调用的函数的地址。
- SYSCALL(restart_syscall)
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SYSCALL(exit)
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PPC_SYS(fork)
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SYSCALL_SPU(read)
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SYSCALL_SPU(write)
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COMPAT_SYS_SPU(open)
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SYSCALL_SPU(close)
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COMPAT_SYS_SPU(waitpid)
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COMPAT_SYS_SPU(creat)
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SYSCALL_SPU(link)
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SYSCALL_SPU(unlink)
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COMPAT_SYS(execve)
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SYSCALL_SPU(chdir)
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COMPAT_SYS_SPU(time)
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SYSCALL_SPU(mknod)
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SYSCALL_SPU(chmod)
当DoSyscall 找到正确的系统调用地址后,它把调用指定的系统调用函数。如要做系统ioctl调用,对应的系统调用号为54,它把调用函数sys_ioctl()。
当函数调用完毕之后,返回到 DoSyscall(),它把控制权切换给 ret_from_except(在
arch/ppc/kernel/entry.S 中定义)。
它会去检查那些在切换回用户空间之前需要完成的任务。如果没有需要做的事情,那么就通过
restore 函数恢复用户进程的状态,并把控制权交还给用户程序。
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