diff options
| author | Tom Lane <tgl@sss.pgh.pa.us> | 2022-03-26 14:29:29 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2022-03-26 14:29:48 -0400 |
| commit | 4fbbea2c1934092581662553fd4be9e84630fc5c (patch) | |
| tree | fae7deb99c19e423c53f6fd6c37ac4ecbbdf5cff | |
| parent | 6e9ffcf13a4a0d56f03b4048231066cb5d061299 (diff) | |
| download | postgresql-4fbbea2c1934092581662553fd4be9e84630fc5c.tar.gz | |
Suppress compiler warning in relptr_store().
clang 13 with -Wextra warns that "performing pointer subtraction with
a null pointer has undefined behavior" in the places where freepage.c
tries to set a relptr variable to constant NULL. This appears to be
a compiler bug, but it's unlikely to get fixed instantly. Fortunately,
we can work around it by introducing an inline support function, which
seems like a good change anyway because it removes the macro's existing
double-evaluation hazard.
Backpatch to v10 where this code was introduced.
Patch by me, based on an idea of Andres Freund's.
Discussion: https://postgr.es/m/48826.1648310694@sss.pgh.pa.us
| -rw-r--r-- | src/include/utils/relptr.h | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/src/include/utils/relptr.h b/src/include/utils/relptr.h index c6bf4e412c..76d48bb37b 100644 --- a/src/include/utils/relptr.h +++ b/src/include/utils/relptr.h @@ -56,11 +56,24 @@ #define relptr_is_null(rp) \ ((rp).relptr_off == 0) +/* We use this inline to avoid double eval of "val" in relptr_store */ +static inline Size +relptr_store_eval(char *base, char *val) +{ + if (val == NULL) + return 0; + else + { + Assert(val > base); + return val - base; + } +} + #ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P #define relptr_store(base, rp, val) \ (AssertVariableIsOfTypeMacro(base, char *), \ AssertVariableIsOfTypeMacro(val, __typeof__((rp).relptr_type)), \ - (rp).relptr_off = ((val) == NULL ? 0 : ((char *) (val)) - (base))) + (rp).relptr_off = relptr_store_eval(base, (char *) (val))) #else /* * If we don't have __builtin_types_compatible_p, assume we might not have @@ -68,7 +81,7 @@ */ #define relptr_store(base, rp, val) \ (AssertVariableIsOfTypeMacro(base, char *), \ - (rp).relptr_off = ((val) == NULL ? 0 : ((char *) (val)) - (base))) + (rp).relptr_off = relptr_store_eval(base, (char *) (val))) #endif #define relptr_copy(rp1, rp2) \ |