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help / color / mirror / Atom feedFrom: Tatsuo Ishii <[email protected]>
To: [email protected]
Subject: warning: dereferencing type-punned pointer
Date: Wed, 24 Jul 2024 15:55:25 +0900 (JST)
Message-ID: <[email protected]> (raw)
Today I compiled PostgreSQL master branch with -fno-strict-aliasing
compile option removed (previous discussions on the $subject [1]). gcc
version is 9.4.0.
There are a few places where $subject warning printed.
In file included from ../../../src/include/nodes/pg_list.h:42,
from ../../../src/include/access/tupdesc.h:19,
from ../../../src/include/access/htup_details.h:19,
from ../../../src/include/access/heaptoast.h:16,
from execExprInterp.c:59:
execExprInterp.c: In function ‘ExecEvalJsonExprPath’:
../../../src/include/nodes/nodes.h:133:29: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
133 | #define nodeTag(nodeptr) (((const Node*)(nodeptr))->type)
| ~^~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/nodes/nodes.h:158:31: note: in expansion of macro ‘nodeTag’
158 | #define IsA(nodeptr,_type_) (nodeTag(nodeptr) == T_##_type_)
| ^~~~~~~
../../../src/include/nodes/miscnodes.h:53:26: note: in expansion of macro ‘IsA’
53 | ((escontext) != NULL && IsA(escontext, ErrorSaveContext) && \
| ^~~
execExprInterp.c:4399:7: note: in expansion of macro ‘SOFT_ERROR_OCCURRED’
4399 | if (SOFT_ERROR_OCCURRED(&jsestate->escontext))
| ^~~~~~~~~~~~~~~~~~~
execExprInterp.c: In function ‘ExecEvalJsonCoercionFinish’:
../../../src/include/nodes/nodes.h:133:29: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
133 | #define nodeTag(nodeptr) (((const Node*)(nodeptr))->type)
| ~^~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/nodes/nodes.h:158:31: note: in expansion of macro ‘nodeTag’
158 | #define IsA(nodeptr,_type_) (nodeTag(nodeptr) == T_##_type_)
| ^~~~~~~
../../../src/include/nodes/miscnodes.h:53:26: note: in expansion of macro ‘IsA’
53 | ((escontext) != NULL && IsA(escontext, ErrorSaveContext) && \
| ^~~
execExprInterp.c:4556:6: note: in expansion of macro ‘SOFT_ERROR_OCCURRED’
4556 | if (SOFT_ERROR_OCCURRED(&jsestate->escontext))
| ^~~~~~~~~~~~~~~~~~~
origin.c: In function ‘StartupReplicationOrigin’:
origin.c:773:16: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
773 | file_crc = *(pg_crc32c *) &disk_state;
| ^~~~~~~~~~~~~~~~~~~~~~~~~
In my understanding from the discussion [1], it would be better to fix
our code to avoid the warning because it *might* point out that there
is something wrong with our code. However the consensus at the time
was, we will not remove -fno-strict-aliasing option for now. It will
take long time before it would happen...
So I think the warnings in ExecEvalJsonExprPath are better fixed
because these are the only places where IsA (nodeTag) macro are used
and the warning is printed. Patch attached.
I am not so sure about StartupReplicationOrigin. Should we fix it now?
For me the code looks sane as long as we keep -fno-strict-aliasing
option. Or maybe better to fix so that someday we could remove the
compiler option?
[1] https://www.postgresql.org/message-id/flat/366.1535731324%40sss.pgh.pa.us#bd93089182d13c79b74593ec70...
Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp
Attachments:
[text/x-patch] fix_ExecEvalJsonExprPath.patch (1.1K, ../[email protected]/2-fix_ExecEvalJsonExprPath.patch)
download | inline diff:
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index d8735286c4..387311fdfb 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -4381,6 +4381,7 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
if (!*op->resnull && jsexpr->use_io_coercion)
{
FunctionCallInfo fcinfo;
+ Node *node;
Assert(jump_eval_coercion == -1);
fcinfo = jsestate->input_fcinfo;
@@ -4396,7 +4397,8 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
fcinfo->isnull = false;
*op->resvalue = FunctionCallInvoke(fcinfo);
- if (SOFT_ERROR_OCCURRED(&jsestate->escontext))
+ node = (Node *) &jsestate->escontext;
+ if (SOFT_ERROR_OCCURRED(node))
error = true;
}
@@ -4552,8 +4554,9 @@ void
ExecEvalJsonCoercionFinish(ExprState *state, ExprEvalStep *op)
{
JsonExprState *jsestate = op->d.jsonexpr.jsestate;
+ Node *node = (Node *) &jsestate->escontext;
- if (SOFT_ERROR_OCCURRED(&jsestate->escontext))
+ if (SOFT_ERROR_OCCURRED(node))
{
*op->resvalue = (Datum) 0;
*op->resnull = true;
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