Re: [PATCH] configure: respect --with-build-time-tools [PR43301]

[Alexandre Oliva <oliva@gnu.org>]

Hello, Eric,

Thanks for looking into this.

On Aug  1, 2022, Eric Gallager via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:

>> This just reassigns the value that was retrieved a couple of lines
>> above from the very same variable.

> Oh, ok, so I guess this isn't necessary after all?

Yeah, I don't see how this patch could make any difference as to the
reported problem.

> In which case we can just close 43301 as INVALID then?

AFAICT, with_build_time_tools is dealt with in the top level configure,
setting up *_FOR_TARGET after searching for the tool names in the
specified location.

However, there's a potentially confusing consequence of the current
code: gcc/configure looks for ./as$build_exeext in the build tree, and
uses that without overwriting it if found, so if an earlier configure
run created an 'as' script, a reconfigure will just use it, without
creating the file again, even if it would have changed
ORIGINAL_AS_FOR_TARGET in it.

I suppose if the patch was tested by the original submitter on a clean
build tree, so it would *appear* to have made a difference in fixing the
problem, while it was actually just a no-op, and the apparent fix was a
consequence of the clean build tree.

So, the patch is not useful, but we may want to avoid the confusing
scenario somehow.

I suppose the point of not creating such a tiny script again is not to
avoid unnecessary rebuilding of dependencies (I don't even see how
dependencies on the script would come into play), so creating it again
wouldn't hurt.  However, we wish to avoid overwriting an assembler
copied into the build tree for use by gcc during the build.  Perhaps:

-elif test -x as$build_exeext; then
+elif test -x as$build_exeext \
+       && { test "x$build_exeext" != "x" \
+            || test "x`grep '^# Invoke as, ld or nm from the build tree' \
+                         as`" = "x"; }; then

WDYT?

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
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