libstdc++ testsuite failures and GLIBCPP_BUILD_PCH

libstdc++ testsuite failures and GLIBCPP_BUILD_PCH

[Janis Johnson]

Testing of libstdc++-v3 for a cross powerpc64-linux compiler fails
because bits/stdc++.h isn't found.  It appears to be a configuration
or build problem, but I don't understand how that mechanism works.

From libstdc++-v3/include/Makefile.am:

if GLIBCPP_BUILD_PCH
pch_build = ${pch_input}
pch_install = install-pch
else
pch_build =
pch_install =
endif

From libstdc++-v3/include/Makefile.in:

@GLIBCPP_BUILD_PCH_TRUE@pch_build = ${pch_input}
@GLIBCPP_BUILD_PCH_FALSE@pch_build =
@GLIBCPP_BUILD_PCH_TRUE@pch_install = install-pch
@GLIBCPP_BUILD_PCH_FALSE@pch_install =

For a native i686-linux build, from
i686-pc-linux-gnu/libstdc++-v3/include/Makefile:

pch_build = ${pch_input}
#pch_build =
pch_install = install-pch
#pch_install =

For a cross build of powerpc64-linux from powerpc-linux, from
powerpc64-linux/libstdc++-v3/include/Makefile:

pch_build = ${pch_input}
pch_build =
pch_install = install-pch
pch_install =

So, what magic is going on with @GLIBCPP_BUILD_PCH_TRUE@ and
@GLIBCPP_BUILD_PCH_FALSE@, and why are they both true for my cross
build?

Janis

Re: libstdc++ testsuite failures and GLIBCPP_BUILD_PCH

[Benjamin Kosnik]

> So, what magic is going on with @GLIBCPP_BUILD_PCH_TRUE@ and
> @GLIBCPP_BUILD_PCH_FALSE@, and why are they both true for my cross
> build?

Hmm.

at libstdc++-v3/configure.in: 406

  GLIBCPP_CHECK_COMPILER_FEATURES
  GLIBCPP_CHECK_PCH

Where GLIBCPP_CHECK_PCH is a macro defined in acinclude.m4 to test if
PCH can be used. This macro is only called in the native case, which
actually is overly-conservative now that I think about it.

Since it doesn't do linking, this might as well get moved up, to line 55.

If you want to do this, and make sure it works for you, patch pre-approved.

-benjamin