On 02/11, Mike Frysinger wrote: > > On Thu, Feb 11, 2010 at 22:24, Roland McGrath wrote: > > > On some machines, single-step into a syscall instruction is no different > > from other user instructions, so the normal SIGTRAP will come afterwards > > anyway. > > > > On other machines, entering the kernel for the syscall instruction defeats > > the normal user-mode effects of single-step being enabled. In that event, > > you want to call tracehook_report_syscall_exit() if single-step is enabled. > > You must pass a nonzero second argument if your arch code is not going to > > generate the normal SIGTRAP associated with having single-stepped into the > > syscall instruction. > > so tracehook_report_syscall_exit() checking TIF_SINGLESTEP only makes > sense when the arch doesnt support hardware single stepping in user > mode ? the Blackfin processor does support hardware single stepping > (and we utilize it in Linux). I'd like to know the answer too ;) But, even if x86 supports hardware single stepping, it does check TIF_SINGLESTEP and pass it to tracehook_report_syscall_exit(step). Consider PTRACE_SINGLESTEP which follows the syscall-entry stop. The tracee gets the trap before return to user-mode. Otherwise, if we just return with X86_EFLAGS_TF, it gets the trap after the next instruction after syscall insn. But I don't know whether blackfin should follow this logic. > also, in reading the kerneldocs for tracehook_report_syscall_exit(), > it says "an attempted system call". should system calls greater than > NR_syscall (-ENOSYS) also get traced ? I'd say yes, but let's wait for Roland's reply. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
