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(build) Patch to fix cp/cfns.gperf building issues

Message ID 1303485121.088925951@www2.webmail.us
State New
Headers show

Commit Message

Nicola Pero April 22, 2011, 3:12 p.m. UTC 
This patch fixes a building annoyance that I had when building on a new
machine (an x86_64 gnu/linux box).

The building failed.  It was down to two problems:

 * due to how I got a copy of the GCC source code on the machine, the timestamp
of each source file was the timestamp of when it was copied to the machine (ie,
a random timestamp from the point of view of the building system).  This caused
the build system to decide that $(srcdir)/cp/cfns.h needed to be rebuilt from
$(srcdir)/cp/cfns.gperf (it didn't, obviously; the source code was trunk with
no changes).

 * when the automated rebuild failed because gperf was not there, it also created
an empty cp/cfns.h, basically corrupting my source tree.  Further attempts to
rebuild (with or without gperf) would then fail due to a missing definition of
"libc_name_p" (because cp/cfns.h now existed, and was newer than cp/cfns.gperf,
it wouldn't be rebuilt, and I was stuck with the empty cp/cfns.h).  Searching
on the internet, I found that a number of people got stuck at this stage and
couldn't finish their build.  So, rather than just manually fixing my source
tree, I'm posting a patch that will remove the problems at the root.

This patch fixes both problems, making the build more robust:

 * it only rebuilds cp/cfns.h when a specific command ("make rebuild-cp-cfns") is used.
   According to the ChangeLogs, cp/cfns.gperf was edited about 5 times in 10 years,
   so it does not seem unreasonable to require developers/maintainers to use an explicit
   command to rebuild cp/cfns.h from cp/cfns.gperf for the once-every-two-years occasion when
   it is changed.  I documented the process clearly in cfns.gperf itself.
   This makes the build more robust for end users, who are not bugged by timestamp
   issues in the source tree causing unexpected rebuilds or complications requiring
   gperf.
   In general, I personally feel that the building system should not depend on the relative
   timestamps of source files unless it's doing something in "maintainer mode" where it's being
   explicitly asked to rebuild one source file from the other.  The average user who downloads
   the GCC source code to build it should not be expected to keep the timestamps of each
   source file religiously unchanged!  Timestamps may change as the source code is moved
   around by users and the building system should not have a problem with that.

 * it fails gracefully when the rebuild is triggered and gperf is not available.  Instead
   of creating en empty cp/cfns.h file, it creates no file at all, so that if you then install
   gperf, it will rebuild cp/cfns.h correctly, and if you don't, you'll keep getting the
   error the gperf is not available (not an error about libc_name_p not being defined),
   which is the correct one.

Ok to commit ?

Thanks

Comments

Joseph Myers April 22, 2011, 5:11 p.m. UTC | #1 
On Fri, 22 Apr 2011, Nicola Pero wrote:

> In general, I personally feel that the building system should not depend 
> on the relative timestamps of source files unless it's doing something 
> in "maintainer mode" where it's being explicitly asked to rebuild one 
> source file from the other.

We have a --enable-maintainer-mode configure option.  I think you should 
use that instead of having a special rule for a particular file.
diff mbox

Patch

Index: cfns.gperf
===================================================================
--- cfns.gperf  (revision 172858)
+++ cfns.gperf  (working copy)
@@ -15,7 +15,18 @@  for more details.
 
 You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
-<http://www.gnu.org/licenses/>.  */
+<http://www.gnu.org/licenses/>.
+
+You need to use gperf to generate cfns.h from cfns.gperf.  This is
+the process:
+
+ have a GCC source/build tree already checked out
+ edit cfns.gperf
+ cd $(buildir)/gcc
+ make rebuild-cp-cfns
+
+Alternatively, just look into cp/Make-lang.in and run the gperf
+command in the rebuild-cp-cfns rule manually.  */
 #ifdef __GNUC__
 __inline
 #endif
Index: Make-lang.in
===================================================================
--- Make-lang.in        (revision 172858)
+++ Make-lang.in        (working copy)
@@ -104,11 +104,19 @@  cc1plus$(exeext): $(CXX_OBJS) cc1plus-checksum.o $
        +$(LINKER) $(ALL_LINKERFLAGS) $(LDFLAGS) -o $@ \
              $(CXX_OBJS) cc1plus-checksum.o $(BACKEND) $(LIBS) $(BACKENDLIBS)
 
-# Special build rules.
-$(srcdir)/cp/cfns.h: $(srcdir)/cp/cfns.gperf
+# Special build rule.  This is a maintainer rule, that needs to be
+# invoked manually (as in "cd $(builddir)/gcc; make rebuild-cp-cfns")
+# to rebuild cfns.h from cfns.gperf any time that cfns.gperf is
+# edited.  We don't trigger it automatically when
+# $(srcdir)/cp/cfns.gperf is newer than $(srcdir)/cp/cfns.h because we
+# don't want to depend on users getting the source code with
+# particular timestamps.
+rebuild-cp-cfns:
        gperf -o -C -E -k '1-6,$$' -j1 -D -N 'libc_name_p' -L ANSI-C \
-               $(srcdir)/cp/cfns.gperf > $(srcdir)/cp/cfns.h
+               $(srcdir)/cp/cfns.gperf --output-file $(srcdir)/cp/cfns.h
 
+.PHONY: rebuild-cp-cfns
+
 #^L
 # Build hooks:
 
Index: ChangeLog
===================================================================
--- ChangeLog   (revision 172858)
+++ ChangeLog   (working copy)
@@ -1,3 +1,13 @@ 
+2011-04-22  Nicola Pero  <nicola.pero@meta-innovation.com>
+
+       * Make-lang.in (rebuild-cp-cfns): New rule replacing the one to
+       build $(srcdir)/cp/cfns.h to prevent unwanted rebuilds.  Use
+       --output-file option of gperf instead of > to prevent creating an
+       empty cp/cfns.h when gperf is not available.
+       (.PHONY): New, to make rebuild-cp-cfns as phony.
+       * cfns.gperf: Explain how to run 'make rebuild-cp-cfns'.
+       * cfns.h: Regenerated
+
 2011-04-20  Jason Merrill  <jason@redhat.com>
 
        * semantics.c (finish_compound_literal): Don't put an array
Index: cfns.h
===================================================================
--- cfns.h      (revision 172858)
+++ cfns.h      (working copy)
@@ -1,5 +1,5 @@ 
 /* ANSI-C code produced by gperf version 3.0.3 */
-/* Command-line: gperf -o -C -E -k '1-6,$' -j1 -D -N libc_name_p -L ANSI-C cfns.gperf  */
+/* Command-line: gperf -o -C -E -k '1-6,$' -j1 -D -N libc_name_p -L ANSI-C --output-file ../../trunk2/gcc/cp/cfns.h ../../trunk2/gcc/cp/cfns.gperf  */
 
 #if !((' ' == 32) && ('!' == 33) && ('"' == 34) && ('#' == 35) \
       && ('%' == 37) && ('&' == 38) && ('\'' == 39) && ('(' == 40) \
@@ -28,7 +28,7 @@ 
 #error "gperf generated tables don't work with this execution character set. Please report a bug to <bug-gnu-gperf@gnu.org>."
 #endif
 
-#line 1 "cfns.gperf"
+#line 1 "../../trunk2/gcc/cp/cfns.gperf"
 
 /* Copyright (C) 2000, 2003 Free Software Foundation, Inc.
 
@@ -46,7 +46,18 @@  for more details.
 
 You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
-<http://www.gnu.org/licenses/>.  */
+<http://www.gnu.org/licenses/>.
+
+You need to use gperf to generate cfns.h from cfns.gperf.  This is
+the process:
+
+ have a GCC source/build tree already checked out
+ edit cfns.gperf
+ cd $(buildir)/gcc
+ make rebuild-cfns
+
+Alternatively, just look into cp/Make-lang.in and run the gperf
+command in the rebuild-cfns rule manually.  */
 #ifdef __GNUC__
 __inline
 #endif