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Add macro to cast away volatile without allowing changes to underlying type

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This adds unvolatize(), which works just like unconstify() but for volatile.

Discussion: https://www.postgresql.org/message-id/flat/7a5cbea7-b8df-e910-0f10-04014bcad701%402ndquadrant.com
This commit is contained in:
Peter Eisentraut 2019-03-25 09:35:29 +01:00
parent 572e3e6634
commit 481018f280
3 changed files with 9 additions and 3 deletions
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2
src/backend/postmaster/pgstat.c
View File

@ -3311,7 +3311,7 @@ pgstat_read_current_status(void)
localentry->backendStatus.st_procpid = beentry->st_procpid;
if (localentry->backendStatus.st_procpid > 0)
{
memcpy(&localentry->backendStatus, (char *) beentry, sizeof(PgBackendStatus));
memcpy(&localentry->backendStatus, unvolatize(PgBackendStatus *, beentry), sizeof(PgBackendStatus));
/*
* strcpy is safe even if the string is modified concurrently,

2
src/backend/storage/ipc/pmsignal.c
View File

@ -134,7 +134,7 @@ PMSignalShmemInit(void)
if (!found)
{
MemSet(PMSignalState, 0, PMSignalShmemSize());
MemSet(unvolatize(PMSignalData *, PMSignalState), 0, PMSignalShmemSize());
PMSignalState->num_child_flags = MaxLivePostmasterChildren();
}
}

8
src/include/c.h
View File

@ -1122,7 +1122,7 @@ typedef union PGAlignedXLogBlock
#endif
/*
* Macro that allows to cast constness away from an expression, but doesn't
* Macro that allows to cast constness and volatile away from an expression, but doesn't
* allow changing the underlying type. Enforcement of the latter
* currently only works for gcc like compilers.
*
@ -1141,9 +1141,15 @@ typedef union PGAlignedXLogBlock
(StaticAssertExpr(__builtin_types_compatible_p(__typeof(expr), const underlying_type), \
"wrong cast"), \
(underlying_type) (expr))
#define unvolatize(underlying_type, expr) \
(StaticAssertExpr(__builtin_types_compatible_p(__typeof(expr), volatile underlying_type), \
"wrong cast"), \
(underlying_type) (expr))
#else
#define unconstify(underlying_type, expr) \
((underlying_type) (expr))
#define unvolatize(underlying_type, expr) \
((underlying_type) (expr))
#endif
/* ----------------------------------------------------------------