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 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 different signedness: ‘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:

--- a/src/include/port/atomics/arch-ppc.h
+++ b/src/include/port/atomics/arch-ppc.h
@@ -96,3 +96,4 @@ pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
if (__builtin_constant_p(*expected) &&
- *expected <= PG_INT16_MAX && *expected >= PG_INT16_MIN)
+ (int32) *expected <= PG_INT16_MAX &&
+ (int32) *expected >= PG_INT16_MIN)
__asm__ __volatile__(
@@ -185,3 +186,4 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
if (__builtin_constant_p(*expected) &&
- *expected <= PG_INT16_MAX && *expected >= PG_INT16_MIN)
+ (int64) *expected <= PG_INT16_MAX &&
+ (int64) *expected >= PG_INT16_MIN)
__asm__ __volatile__(