Android arm linux 系統(tǒng)調(diào)用實現(xiàn)

Linux的應(yīng)用程序要想訪問內(nèi)核必須使用系統(tǒng)調(diào)用從而實現(xiàn)從usr模式轉(zhuǎn)到svc模式。在arm中，這個過程是通過swi(或者和它等價的指令)來實現(xiàn)模式轉(zhuǎn)換的。

從bionic libc中的open函數(shù)追溯系統(tǒng)調(diào)用實現(xiàn)

相關(guān)文件：

• bionic/libc/unistd/open.c

• bionic/libc/arch-arm/syscalls/__open.S

• linux/arch/arm/kernel/entry-common.S

• linux/arch/arm/kernel/entry-armv.S

• linux/arch/arm/kernel/entry-header.S

相關(guān)調(diào)用過程：

• int open(const char *pathname, int flags, ...);bionic/libc/unistd/open.c

• __openbionic/libc/arch-arm/syscalls/__open.S

  __open:

  .save {r4, r7}

  stmfd sp!, {r4, r7}

  ldr r7, =__NR_open

  swi #0

  ldmfd sp!, {r4, r7}

  movs r0, r0

  bxpl lr

  b __set_syscall_errno

• vector_swilinux/arch/arm/kernel/entry-common.S

  adr tbl, sys_call_table @ load syscall table pointer

  cmp scno, #NR_syscalls @ check upper syscall limit

  adr lr, BSYM(ret_fast_syscall) @ return address

  ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine

• sys_call_table系統(tǒng)調(diào)用跳轉(zhuǎn)表，里面保存了各個系統(tǒng)調(diào)用實現(xiàn)的地址。

  .type sys_call_table, #object

  ENTRY(sys_call_table)

  #include "calls.S"