diff options
| author | Tom Lane | 2022-03-26 18:29:29 +0000 |
|---|---|---|
| committer | Tom Lane | 2022-03-26 18:29:56 +0000 |
| commit | a2a1aa830a1ccf6991c59a64c6f2b873f3c2c727 (patch) | |
| tree | 14326d50e34cd450df1dcc9d3542b132bdf1ad76 /src/include/utils | |
| parent | 3d263b09058a6ea90ed0f6143fafbb92892c7ba8 (diff) | |
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
Diffstat (limited to 'src/include/utils')
| -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 4b74571e91d..888e10d727d 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) \ |