Re: [PATCH] gcc/configure.ac: add --disable-systemtap switch

[Eric Gallager <egall@gwmail.gwu.edu>]

On 5/24/18, Jeff Law <law@redhat.com> wrote:
> On 05/12/2018 08:00 AM, Sergei Trofimovich via gcc-patches wrote:
>> From: Sergei Trofimovich <slyfox@gentoo.org>
>>
>> Before the change systemtap probes were enabled
>> if target headers had sys/sdt.h at ./configure time.
>>
>> After the change explicitly ask to enable or disable
>> for probe support and not rely on automagic dependency
>> discovery.
> I'm not terribly concerned about the uninstalling systemtap while
> compiling gcc problem.   That seems like a package management problem on
> the distro side.
>
> 61257 does raise the issue of header file usability which is a much
> bigger concern.  c#1 indicates autoconf-2.70 introduces code which
> instead of testing for header file existence instead checks for
> usability.  So I'd rather see us moving towards making that happen
> rather than explicit enable/disable of systemtap headers/probes.
>
> jeff
>

I retracted c#1 in c#4. What autoconf-2.70 changes is how the
AC_CHECK_HEADERS macro is expanded. In current versions of autoconf,
AC_CHECK_HEADERS checks for header file usability, presence, and
existence, but allows the latter 2 to override the usability check. In
autoconf-2.70, however, AC_CHECK_HEADERS will *only* do the usability
check. However, after looking at the code in question, I found that
AC_CHECK_HEADERS is not even used here, but rather it just does `test
-f`. Thus the autoconf-2.70 changes won't automatically fix anything,
since `test -f` is at the shellcode level rather than the m4 level. So
we don't need to wait for it to be released, and probably shouldn't
anyways, considering how many years its release has been pending.

Eric