Re: powerpc pg_atomic_compare_exchange_u32_impl: error: comparison of integer expressions of different signedness (Re: pgsql: For all ppc compilers, implement compare_exchange and) fetch_add

On Fri, Oct 09, 2020 at 03:01:17AM -0700, Noah Misch wrote:
> On Fri, Oct 09, 2020 at 11:28:25AM +0200, Christoph Berg wrote:
> > pg-cron on powerpc/ppc64/ppc64el is raising this warning inside the
> > ppc atomics:
> > 
> > gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels
-Wmissing-format-attribute-Wimplicit-fallthrough=3 -Wformat-security -fno-strict-aliasing -fwrapv
-fexcess-precision=standard-Wno-format-truncation -Wno-stringop-truncation -g -g -O2 -fstack-protector-strong -Wformat
-Werror=format-security-g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat
-Werror=format-security-fPIC -std=c99 -Wall -Wextra -Werror -Wno-unknown-warning-option -Wno-unused-parameter
-Wno-maybe-uninitialized-Wno-implicit-fallthrough -Iinclude -I/usr/include/postgresql -I. -I./
-I/usr/include/postgresql/13/server-I/usr/include/postgresql/internal  -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE
-I/usr/include/libxml2  -c -o src/job_metadata.o src/job_metadata.c
 
> > In file included from /usr/include/postgresql/13/server/port/atomics.h:74,
> >                  from /usr/include/postgresql/13/server/utils/dsa.h:17,
> >                  from /usr/include/postgresql/13/server/nodes/tidbitmap.h:26,
> >                  from /usr/include/postgresql/13/server/access/genam.h:19,
> >                  from src/job_metadata.c:21:
> > /usr/include/postgresql/13/server/port/atomics/arch-ppc.h: In function ‘pg_atomic_compare_exchange_u32_impl’:
> > /usr/include/postgresql/13/server/port/atomics/arch-ppc.h:97:42: error: comparison of integer expressions of
differentsignedness: ‘uint32’ {aka ‘unsigned int’} and ‘int’ [-Werror=sign-compare]
 
> >    97 |   *expected <= PG_INT16_MAX && *expected >= PG_INT16_MIN)
> >       |                                          ^~
> > src/job_metadata.c: At top level:
> > cc1: note: unrecognized command-line option ‘-Wno-unknown-warning-option’ may have been intended to silence earlier
diagnostics
> > cc1: all warnings being treated as errors
> > 
> > Looking at the pg_atomic_compare_exchange_u32_impl, this looks like a
> > genuine problem:
> > 
> > static inline bool
> > pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
> >                                     uint32 *expected, uint32 newval)
> > ...
> >     if (__builtin_constant_p(*expected) &&
> >         *expected <= PG_INT16_MAX && *expected >= PG_INT16_MIN)
> > 
> > If *expected is an unsigned integer, comparing it to PG_INT16_MIN
> > which is a negative number doesn't make sense.
> > 
> > src/include/c.h:#define PG_INT16_MIN    (-0x7FFF-1)
> 
> Agreed.  I'll probably fix it like this:

The first attachment fixes the matter you've reported.  While confirming that,
I observed that gcc builds don't even use the 64-bit code in arch-ppc.h.
Oops.  The second attachment fixes that.  I plan not to back-patch either of
these.