Arm Linux系统调用流程详细解析

最后再罗嗦一点，如果用sys_open来搜的话，是搜不到系统调用open的定义的，系统调用函数都是用宏来定义的，比如对于open，在文件fs/open.c文件中这样定义：

SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, int, mode){long ret;if (force_o_largefile())flags = O_LARGEFILE;ret = do_sys_open(AT_FDCWD, filename, flags, mode);/* avoid REGPARM breakage on x86: */asmlinkage_protect(3, ret, filename, flags, mode);return ret;}

继续回到vector_swi，而如果系统调用号不正确，则会调用arm_syscall函数来进行处理，这个函数在文件arch/arm/kernel/traps.c中定义：

/** Handle all unrecognised system calls.*  0x9f0 - 0x9fffff are some more esoteric system calls*/#define NR(x) ((__ARM_NR_##x) - __ARM_NR_BASE)asmlinkage int arm_syscall(int no, struct pt_regs *regs){struct thread_info *thread = current_thread_info();siginfo_t info;if ((no >> 16) != (__ARM_NR_BASE>> 16))return bad_syscall(no, regs);switch (no & 0xffff) {case 0: /* branch through 0 */info.si_signo = SIGSEGV;info.si_errno = 0;info.si_code  = SEGV_MAPERR;info.si_addr  = NULL;arm_notify_die("branch through zero", regs, &info, 0, 0);return 0;case NR(breakpoint): /* SWI BREAK_POINT */regs->ARM_pc -= thumb_mode(regs) ? 2 : 4;ptrace_break(current, regs);return regs->ARM_r0;/** Flush a region from virtual address r0 to virtual address r1* _exclusive_.  There is no alignment requirement on either address;* user space does not need to know the hardware cache layout.** r2 contains flags.  It should ALWAYS be passed as ZERO until it* is defined to be something else.  For now we ignore it, but may* the fires of hell burn in your belly if you break this rule. ;)** (at a later date, we may want to allow this call to not flush* various aspects of the cache.  Passing 0 will guarantee that* everything necessary gets flushed to maintain consistency in* the specified region).*/case NR(cacheflush):do_cache_op(regs->ARM_r0, regs->ARM_r1, regs->ARM_r2);return 0;case NR(usr26):if (!(elf_hwcap & HWCAP_26BIT))break;regs->ARM_cpsr &= ~MODE32_BIT;return regs->ARM_r0;case NR(usr32):if (!(elf_hwcap & HWCAP_26BIT))break;regs->ARM_cpsr = MODE32_BIT;return regs->ARM_r0;case NR(set_tls):thread->tp_value = regs->ARM_r0;if (tls_emu)return 0;if (has_tls_reg) {asm ("mcr p15, 0, %0, c13, c0, 3": : "r" (regs->ARM_r0));} else {/** User space must never try to access this directly.* Expect your app to break eventually if you do so.* The user helper at 0xffff0fe0 must be used instead.* (see entry-armv.S for details)*/*((unsigned int *)0xffff0ff0) = regs->ARM_r0;}return 0;#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG/** Atomically store r1 in *r2 if *r2 is equal to r0 for user space.* Return zero in r0 if *MEM was changed or non-zero if no exchange* happened.  Also set the user C flag accordingly.* If access permissions have to be fixed up then non-zero is* returned and the operation has to be re-attempted.** *NOTE*: This is a ghost syscall private to the kernel.  Only the* __kuser_cmpxchg code in entry-armv.S should be aware of its* existence.  Dont ever use this from user code.*/case NR(cmpxchg):for (;;) {extern void do_DataAbort(unsigned long addr, unsigned int fsr,struct pt_regs *regs);unsigned long val;unsigned long addr = regs->ARM_r2;struct mm_struct *mm = current->mm;pgd_t *pgd; pmd_t *pmd; pte_t *pte;spinlock_t *ptl;regs->ARM_cpsr &= ~PSR_C_BIT;down_read(&mm->mmap_sem);pgd = pgd_offset(mm, addr);if (!pgd_present(*pgd))goto bad_access;pmd = pmd_offset(pgd, addr);if (!pmd_present(*pmd))goto bad_access;pte = pte_offset_map_lock(mm, pmd, addr, &ptl);i