Linux process segfault at xx error N in IP
进程异常退出，看内核日志(/var/log/messages)有如下信息：
Dec 29 18:33:58 t430 kernel: [34217.713018] test_common[29453]: segfault at 7f0484aef1d0 ip 0000557b7c60c5c7 sp 00007ffc3a9f38a0 error 4 in test_common[557b7c609000+43000]
1 error分析
Segfault一般是由内存访问越界导致的。error数值含义如下：
| 位 | 含义 |
| 0 | 0表示对应地址没有page，1表示保护异常 |
| 1 | 0表示读访问异常，1表示写访问异常 |
| 2 | 0内核访问异常，1表示用户态访问异常 |
error=4(0b100)用户态读访问地址无效， error=6(0b110)用户态写访问地址无效。
2 参考代码
linux/arch/x86/include/asm/traps.h:
/* * Page fault error code bits: * * bit 0 == 0: no page found 1: protection fault * bit 1 == 0: read access 1: write access * bit 2 == 0: kernel-mode access 1: user-mode access * bit 3 == 1: use of reserved bit detected * bit 4 == 1: fault was an instruction fetch * bit 5 == 1: protection keys block access */ enum x86_pf_error_code { X86_PF_PROT = 1 << 0, X86_PF_WRITE = 1 << 1, X86_PF_USER = 1 << 2, X86_PF_RSVD = 1 << 3, X86_PF_INSTR = 1 << 4, X86_PF_PK = 1 << 5, };
static inline void show_signal_msg(struct pt_regs *regs, unsigned long error_code, unsigned long address, struct task_struct *tsk) { const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; if (!unhandled_signal(tsk, SIGSEGV)) return; if (!printk_ratelimit()) return; printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", loglvl, tsk->comm, task_pid_nr(tsk), address, (void *)regs->ip, (void *)regs->sp, error_code); print_vma_addr(KERN_CONT " in ", regs->ip); printk(KERN_CONT "\n"); show_opcodes(regs, loglvl); }