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Fix incorrect parallel build of jsonapi.o with Makefiles.

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Commit 0785d1b8b wrote

jsonapi_shlib.o: override CPPFLAGS += -DJSONAPI_USE_PQEXPBUFFER

forgetting that GNU make treats this change to CPPFLAGS as affecting
not only jsonapi_shlib.o, but anything that gets built in pursuit of
building jsonapi_shlib.o.  Because of an even more ancient hack
(cf 7143b3e82), that will include jsonapi.o if it's not been built
already.  If we do apply this -D switch to jsonapi.o, it gets built
with the wrong expansible-string infrastructure, which manifests
immediately as a link failure in pg_combinebackup and would misbehave
at runtime even if the build somehow completed.

Perhaps remarkably, we'd not seen field reports of build failures
till now, but it's pretty easy to reproduce a mis-build by trying
to build src/common/ with --shuffle and a high -j factor.

To fix, don't modify CPPFLAGS this way; instead make a dedicated
build rule for jsonapi_shlib.o that injects the additional switches.

There might be other places with similar problems, but some desultory
attempts with -j32 --shuffle on a 32-thread CPU didn't find any more
build failures.  Also, it looks like the meson build infrastructure
lacks this problem (but I'm no meson expert).

Bug: #19727
Reported-by: Ross Burton <ross@burtonini.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Ross Burton <ross@burtonini.com>
Discussion: https://postgr.es/m/19727-32d67d9dea410f38@postgresql.org
Backpatch-through: 18
This commit is contained in:
Tom Lane
2026-09-30 15:58:33 -04:00
parent c5666f7e16
commit a70876d7bf
1 changed files with 6 additions and 5 deletions
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11
src/common/Makefile
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@@ -160,11 +160,6 @@ libpgcommon_shlib.a: $(OBJS_SHLIB)
rm -f $@
$(AR) $(AROPT) $@ $^
# The JSON API normally exits on out-of-memory; disable that behavior for shared
# library builds. This requires libpq's pqexpbuffer.h.
jsonapi_shlib.o: override CPPFLAGS += -DJSONAPI_USE_PQEXPBUFFER
jsonapi_shlib.o: override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
# Because this uses its own compilation rule, it doesn't use the
# dependency tracking logic from Makefile.global. To make sure that
# dependency tracking works anyway for the *_shlib.o files, depend on
@@ -174,6 +169,12 @@ jsonapi_shlib.o: override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
%_shlib.o: %.c %.o
$(CC) $(CFLAGS) $(CFLAGS_SL) $(CPPFLAGS) -c $< -o $@
# The JSON API normally exits on out-of-memory; disable that behavior for shared
# library builds. This requires libpq's pqexpbuffer.h.
# This rule overrides the previous one, so must duplicate all its effects.
jsonapi_shlib.o: jsonapi.c jsonapi.o
$(CC) $(CFLAGS) $(CFLAGS_SL) -DJSONAPI_USE_PQEXPBUFFER -I$(libpq_srcdir) $(CPPFLAGS) -c $< -o $@
libpgcommon_excluded_shlib.a: $(OBJS_EXCLUDED_SHLIB)
rm -f $@
$(AR) $(AROPT) $@ $^