Re: [PATCH] S390: Sync ptrace.h with kernel. [BZ #21539]

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

On 07/04/2017 11:41 AM, Florian Weimer wrote:
> On 07/04/2017 10:22 AM, Stefan Liebler wrote:
> > +      /* Ptrace request 12 is done with zero data argument:
> > +	 -If the kernel has support for PTRACE_SINGLEBLOCK (then the kernel
> > +	 header asm/ptrace.h defines this macro), the ptrace call is not allowed
> > +	 to fail and has to continue the tracee until next taken branch.
>
> I think this is still bogus.  We can compile with newer kernel headers
> than the host kernel, and this will cause the test to fail.
>
> Thanks,
> Florian

Okay.
So I can check the return value of the second ptrace (req_singleblock, 
pid, NULL, NULL) call at runtime to determine the kernel-support:

      errno = 0;
      ret = ptrace (req_singleblock, pid, NULL, NULL);
      if (ret == 0)
	{
	  /* The kernel has support for PTRACE_SINGLEBLOCK ptrace request. */
	  TEST_VERIFY_EXIT (errno == 0);
	}
      else
	{
	  /* The kernel (< 3.15) has no support for PTRACE_SINGLEBLOCK ptrace
	     request. */
	  TEST_VERIFY_EXIT (errno == EIO);
	  TEST_VERIFY_EXIT (ret == -1);

	  /* Just continue tracee until it exits normally.  */
	  TEST_VERIFY_EXIT (ptrace (PTRACE_CONT, pid, NULL, NULL) == 0);
	}



Then the test runs on kernels with / without support for 
PTRACE_SINGLEBLOCK. The first ptrace call ensures that request 12 is not 
interpreted as PTRACE_GETREGS.

Bye.
Stefan