Arm Linux系统调用流程详细解析SWI

两个宏都配置 行为就是上面说的那样

第二 只配置CONFIG_OABI_COMPAT ， 那么以old ABI方式调用的会用sys_oabi_call_table，以EABI方式调用的 用sys_call_table，和1实质相同，只是情况1更加明确。

第三 只配置CONFIG_AEABI 系统中不存在 sys_oabi_call_table， 对old ABI方式调用不兼容。只能 以EABI方式调用，用sys_call_table

第四 两个都没有配置 系统默认会只允许old ABI方式，但是不存在old_syscall_table，最终会通过sys_call_table 完成函数调用

可以参考下面的代码
对我们的项目比较有用。

.align 5 ENTRY(vector_swi) sub sp, sp, #S_FRAME_SIZE stmia sp, {r0 - r12} @ Calling r0 - r12 add r8, sp, #S_PC stmdb r8, {sp, lr}^ @ Calling sp, lr mrs r8, spsr @ called from non-FIQ mode, so ok. str lr, [sp, #S_PC] @ Save calling PC str r8, [sp, #S_PSR] @ Save CPSR str r0, [sp, #S_OLD_R0] @ Save OLD_R0 zero_fp /* * Get the system call number. */ #if defined(CONFIG_OABI_COMPAT) /* * If we have CONFIG_OABI_COMPAT then we need to look at the swi * value to determine if it is an EABI or an old ABI call. */ #ifdef CONFIG_ARM_THUMB tst r8, #PSR_T_BIT movne r10, #0 @ no thumb OABI emulation ldreq r10, [lr, #-4] @ get SWI instruction #else ldr r10, [lr, #-4] @ get SWI instruction A710( and ip, r10, #0x0f000000 @ check for SWI ) A710( teq ip, #0x0f000000 ) A710( bne .Larm710bug ) #endif #elif defined(CONFIG_AEABI) /* * Pure EABI user space always put syscall number into scno (r7). */ A710( ldr ip, [lr, #-4] @ get SWI instruction ) A710( and ip, ip, #0x0f000000 @ check for SWI ) A710( teq ip, #0x0f000000 ) A710( bne .Larm710bug ) #elif defined(CONFIG_ARM_THUMB) /* Legacy ABI only, possibly thumb mode. */ tst r8, #PSR_T_BIT @ this is SPSR from save_user_regs addne scno, r7, #__NR_SYSCALL_BASE @ put OS number in ldreq scno, [lr, #-4] #else /* Legacy ABI only. */ ldr scno, [lr, #-4] @ get SWI instruction A710( and ip, scno, #0x0f000000 @ check for SWI ) A710( teq ip, #0x0f000000 ) A710( bne .Larm710bug ) #endif #ifdef CONFIG_ALIGNMENT_TRAP ldr ip, __cr_alignment ldr ip, [ip] mcr p15, 0, ip, c1, c0 @ update control register #endif enable_irq get_thread_info tsk adr tbl, sys_call_table @ load syscall table pointer ldr ip, [tsk, #TI_FLAGS] @ check for syscall tracing #if defined(CONFIG_OABI_COMPAT) /* * If the swi argument is zero, this is an EABI call and we do nothing. * * If this is an old ABI call, get the syscall number into scno and * get the old ABI syscall table address. */ bics r10, r10, #0xff000000 eorne scno, r10, #__NR_OABI_SYSCALL_BASE ldrne tbl, =sys_oabi_call_table #elif !defined(CONFIG_AEABI) bic scno, scno, #0xff000000 @ mask off SWI op-code eor scno, scno, #__NR_SYSCALL_BASE @ check OS number #endif stmdb sp!, {r4, r5} @ push fifth and sixth args tst ip, #_TIF_SYSCALL_TRACE @ are we tracing syscalls? bne __sys_trace cmp scno, #NR_syscalls @ check upper syscall limit adr lr, ret_fast_syscall @ return address ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine add r1, sp, #S_OFF 2: mov why, #0 @ no longer a real syscall cmp scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE) eor r0, scno, #__NR_SYSCALL_BASE @ put OS number back bcs arm_syscall b sys_ni_syscall @ not private func /* * This is the really slow path. Were going to be doing * context switches, and waiting for our parent to respond. */ __sys_trace: mov r2, scno add r1, sp, #S_OFF mov r0, #0 @ trace entry [IP = 0] bl syscall_trace adr lr, __sys_trace_return @ return address mov scno, r0 @ syscall number (possibly new) add r1, sp, #S_R0 + S_OFF @ pointer to regs cmp scno, #NR_syscalls @ check upper syscall limit ldmccia r1, {r0 - r3} @ have to reload r0 - r3 ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine 

系统调用是os操作系统提供的服