From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ross Burton <ross@burtonini.com>
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19727: pg-combinebackup fails to link
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Comments: In-reply-to Ross Burton <ross@burtonini.com>
	message dated "Wed, 30 Sep 2026 12:10:15 +0100"
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Date: Wed, 30 Sep 2026 09:36:07 -0400
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Ross Burton <ross@burtonini.com> writes:
> I now have a build tree that works and a build tree that breaks, from
> the same machine and environment, simply by re-running the build with
> make --shuffle.

> The working jsonapi.o has functions like appendStringInfoChar,
> resetStringInfo, etc.  The one that fails to link has
> appendPQExpBufferChar, resetPQExpBuffer, etc.

> This is a makefile dependency bug exposed in parallel builds, and can
> be reproduced on demand with a minimal reproducer.  From a clean but
> configured tree, in src/common:

> $ make jsonapi.o
> $ readelf -sW jsonapi.o | grep reset
>     64: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND resetStringInfo

> This builds a jsonapi.o using the direct target, and
> JSONAPI_USE_PQEXPBUFFER is not defined.

> $ make clean
> $ make jsonapi_shlib.o
> $ readelf -sW jsonapi.o | grep reset
>     65: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND resetPQExpBuffer

> This builds jsonapi_shlib.o, which adds JSONAPI_USE_PQEXPBUFFER to
> CPPFLAGS. However jsonapi.o hasn't been built yet so that is also
> built, but with the PQEXPBUFFER define set this time.

Very interesting!  So the problem is that the scope of the effects of
this:

jsonapi_shlib.o: override CPPFLAGS += -DJSONAPI_USE_PQEXPBUFFER

isn't terribly well-defined.  Looking at the rest of that Makefile,
I'm also suspicious about

$(OBJS_FRONTEND): CPPFLAGS += -DUSE_PRIVATE_ENCODING_FUNCS

Can you break that part?  If not, maybe the problem is the
gratuitous-looking "override"?

			regards, tom lane