pg.ddx.io pgsql-hackers@postgresql.org mailing list archive help / color / mirror / Atom feed From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@enterprisedb.com>
Subject: Re: Large writable variables
Date: Thu, 18 Oct 2018 22:17:55 +0200
Message-ID: <08adbe4e-38f8-2c73-55f0-591392371687@2ndquadrant.com> (raw )
In-Reply-To: <20181017215106.esosgw7qfnfavcdw@alap3.anarazel.de >
References: <20181015200754.7y7zfuzsoux2c4ya@alap3.anarazel.de >
<20181016045051.wr35ubb6h7h3ee2b@alap3.anarazel.de >
<20181016050200.c65yjz2qgxulgouv@alap3.anarazel.de >
<20181016063013.kigj6e5pqx6n75y3@alap3.anarazel.de >
<200cf391-4a60-4c69-85d8-c715c7bce4de@2ndquadrant.com >
<20181017200200.t752esxtgnefktu3@alap3.anarazel.de >
<e0c988b9-9df8-51f2-b963-94e27816c622@2ndquadrant.com >
<20181017215106.esosgw7qfnfavcdw@alap3.anarazel.de >
On 17/10/2018 23:51, Andres Freund wrote:
>> __builtin_types_compatible_p(const char *, char *) returns false (0) for me.
>
> Right, that's why I added a const, inside the macro, to the type
> specified in the unconstify argument. So typeof() yields a const char *,
> and the return type is specified as char *, and adding a const in the
> argument also yields a const char *.
Yeah, that works. The C++-inspired version also allowed casting from
not-const to const, which we don't really need.
I'd perhaps change the signature
#define unconstify(underlying_type, var)
because the "var" doesn't actually have to be a variable.
Attached is my previous patch adapted to your macro.
I'm tempted to get rid of the stuff in dfmgr.c and just let the "older
platforms" get the warning.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Attachments:
v2-0001-Apply-unconstify-in-more-places.patch (text/plain, 3.8K) download
From 54693f7201aa4768509c5d6939961b50a9021bcf Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Thu, 18 Oct 2018 22:11:44 +0200
Subject: [PATCH v2] Apply unconstify() in more places
---
src/backend/utils/adt/json.c | 4 ++--
src/backend/utils/adt/misc.c | 2 +-
src/backend/utils/adt/varlena.c | 4 ++--
src/backend/utils/fmgr/dfmgr.c | 4 ++--
src/port/win32setlocale.c | 2 +-
5 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 6f0fe94d63..f47a498228 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -207,12 +207,12 @@ IsValidJsonNumber(const char *str, int len)
*/
if (*str == '-')
{
- dummy_lex.input = (char *) str + 1;
+ dummy_lex.input = unconstify(char *, str) + 1;
dummy_lex.input_length = len - 1;
}
else
{
- dummy_lex.input = (char *) str;
+ dummy_lex.input = unconstify(char *, str);
dummy_lex.input_length = len;
}
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index 6ea3679835..309eb2935c 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -423,7 +423,7 @@ pg_get_keywords(PG_FUNCTION_ARGS)
HeapTuple tuple;
/* cast-away-const is ugly but alternatives aren't much better */
- values[0] = (char *) ScanKeywords[funcctx->call_cntr].name;
+ values[0] = unconstify(char *, ScanKeywords[funcctx->call_cntr].name);
switch (ScanKeywords[funcctx->call_cntr].category)
{
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index a5e812d026..0fd3b15748 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -182,7 +182,7 @@ char *
text_to_cstring(const text *t)
{
/* must cast away the const, unfortunately */
- text *tunpacked = pg_detoast_datum_packed((struct varlena *) t);
+ text *tunpacked = pg_detoast_datum_packed(unconstify(text *, t));
int len = VARSIZE_ANY_EXHDR(tunpacked);
char *result;
@@ -213,7 +213,7 @@ void
text_to_cstring_buffer(const text *src, char *dst, size_t dst_len)
{
/* must cast away the const, unfortunately */
- text *srcunpacked = pg_detoast_datum_packed((struct varlena *) src);
+ text *srcunpacked = pg_detoast_datum_packed(unconstify(text *, src));
size_t src_len = VARSIZE_ANY_EXHDR(srcunpacked);
if (dst_len > 0)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 4a5cc7cfc7..d200b960d2 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -126,7 +126,7 @@ load_external_function(const char *filename, const char *funcname,
* should declare its second argument as "const char *", but older
* platforms might not, so for the time being we just cast away const.
*/
- retval = (PGFunction) dlsym(lib_handle, (char *) funcname);
+ retval = (PGFunction) dlsym(lib_handle, unconstify(char *, funcname));
if (retval == NULL && signalNotFound)
ereport(ERROR,
@@ -175,7 +175,7 @@ PGFunction
lookup_external_function(void *filehandle, const char *funcname)
{
/* as above, cast away const for the time being */
- return (PGFunction) dlsym(filehandle, (char *) funcname);
+ return (PGFunction) dlsym(filehandle, unconstify(char *, funcname));
}
diff --git a/src/port/win32setlocale.c b/src/port/win32setlocale.c
index 0597c2afca..a8cf170dd1 100644
--- a/src/port/win32setlocale.c
+++ b/src/port/win32setlocale.c
@@ -183,7 +183,7 @@ pgwin32_setlocale(int category, const char *locale)
* forbidden to modify, so casting away the "const" is innocuous.
*/
if (result)
- result = (char *) map_locale(locale_map_result, result);
+ result = unconstify(char *, map_locale(locale_map_result, result));
return result;
}
base-commit: e74dd00f53cd6dc1887f76b9672e5f6dcf0fd8a2
--
2.19.1
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To: pgsql-hackers@postgresql.org
Cc: peter.eisentraut@2ndquadrant.com, andres@anarazel.de, thomas.munro@enterprisedb.com
Subject: Re: Large writable variables
In-Reply-To: <08adbe4e-38f8-2c73-55f0-591392371687@2ndquadrant.com>
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