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Date: Thu, 15 Oct 2015 19:32:57 +0000
From: "Moore, Robert" <robert.moore@...el.com>
To: Joe Perches <joe@...ches.com>
CC: LABBE Corentin <clabbe.montjoie@...il.com>,
"Zheng, Lv" <lv.zheng@...el.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
"lenb@...nel.org" <lenb@...nel.org>,
"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
"devel@...ica.org" <devel@...ica.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Box, David E" <david.e.box@...el.com>
Subject: RE: [PATCH] acpi: set return value to const char for some functions
> Please describe the effects of "const pollution".
>
> Why isn't it useful to update the functions that don't modify function
> pointer arguments to const?
It's not that const isn't useful, but it can create problems, especially in existing code. It can bubble up to higher functions, causing lots of changes to existing variables and the definition of existing functions. Not to mention lots of casting and recasting.
Example quote:
"if you started to use "const" for some methods you usually forced to use this in most of your code. But the time spent for maintaining (typing, recompiling when some const is missing, etc.) of const-correctness in code seems greater than for fixing of possible (very rare) problems caused by not using of const-correctness at all."
Also, ACPICA has to be additionally careful because it must compile with many different C compilers.
All that being said, I went ahead and made the actual ACPICA changes corresponding to your patches. There were no pollution issues, and it actually simplified the code by eliminating the need for some uses of ACPI_CAST_PTR.
The only issue I found was here, so we won't do this one:
const char
AcpiUtHexToAsciiChar
\acpica\source\include\acutils.h(322) :
warning C4180: qualifier applied to function type has no meaning; ignored
Here is the current patch to the actual ACPICA code (which is in a different format than the Linux version of the code):
diff --git a/source/components/namespace/nsxfname.c b/source/components/namespace/nsxfname.c
index 51cc4f4..c368c1f 100644
--- a/source/components/namespace/nsxfname.c
+++ b/source/components/namespace/nsxfname.c
@@ -249,7 +249,7 @@ AcpiGetName (
{
ACPI_STATUS Status;
ACPI_NAMESPACE_NODE *Node;
- char *NodeName;
+ const char *NodeName;
/* Parameter validation */
diff --git a/source/components/utilities/utdecode.c b/source/components/utilities/utdecode.c
index 580f891..3d927f5 100644
--- a/source/components/utilities/utdecode.c
+++ b/source/components/utilities/utdecode.c
@@ -191,7 +191,7 @@ const char *AcpiGbl_RegionTypes[ACPI_NUM_PREDEFINED_REGIONS] =
};
-char *
+const char *
AcpiUtGetRegionName (
UINT8 SpaceId)
{
@@ -213,7 +213,7 @@ AcpiUtGetRegionName (
return ("InvalidSpaceId");
}
- return (ACPI_CAST_PTR (char, AcpiGbl_RegionTypes[SpaceId]));
+ return (AcpiGbl_RegionTypes[SpaceId]);
}
@@ -241,7 +241,7 @@ static const char *AcpiGbl_EventTypes[ACPI_NUM_FIXED_EVENTS] =
};
-char *
+const char *
AcpiUtGetEventName (
UINT32 EventId)
{
@@ -251,7 +251,7 @@ AcpiUtGetEventName (
return ("InvalidEventID");
}
- return (ACPI_CAST_PTR (char, AcpiGbl_EventTypes[EventId]));
+ return (AcpiGbl_EventTypes[EventId]);
}
@@ -316,21 +316,21 @@ static const char *AcpiGbl_NsTypeNames[] =
};
-char *
+const char *
AcpiUtGetTypeName (
ACPI_OBJECT_TYPE Type)
{
if (Type > ACPI_TYPE_INVALID)
{
- return (ACPI_CAST_PTR (char, AcpiGbl_BadType));
+ return (AcpiGbl_BadType);
}
- return (ACPI_CAST_PTR (char, AcpiGbl_NsTypeNames[Type]));
+ return (AcpiGbl_NsTypeNames[Type]);
}
-char *
+const char *
AcpiUtGetObjectTypeName (
ACPI_OPERAND_OBJECT *ObjDesc)
{
@@ -372,7 +372,7 @@ AcpiUtGetObjectTypeName (
*
******************************************************************************/
-char *
+const char *
AcpiUtGetNodeName (
void *Object)
{
@@ -448,7 +448,7 @@ static const char *AcpiGbl_DescTypeNames[] =
};
-char *
+const char *
AcpiUtGetDescriptorName (
void *Object)
{
@@ -463,9 +463,7 @@ AcpiUtGetDescriptorName (
return ("Not a Descriptor");
}
- return (ACPI_CAST_PTR (char,
- AcpiGbl_DescTypeNames[ACPI_GET_DESCRIPTOR_TYPE (Object)]));
-
+ return (AcpiGbl_DescTypeNames[ACPI_GET_DESCRIPTOR_TYPE (Object)]);
}
@@ -542,7 +540,7 @@ AcpiUtGetReferenceName (
/* Names for internal mutex objects, used for debug output */
-static char *AcpiGbl_MutexNames[ACPI_NUM_MUTEX] =
+static const char *AcpiGbl_MutexNames[ACPI_NUM_MUTEX] =
{
"ACPI_MTX_Interpreter",
"ACPI_MTX_Namespace",
@@ -552,7 +550,7 @@ static char *AcpiGbl_MutexNames[ACPI_NUM_MUTEX] =
"ACPI_MTX_Memory",
};
-char *
+const char *
AcpiUtGetMutexName (
UINT32 MutexId)
{
diff --git a/source/components/utilities/uthex.c b/source/components/utilities/uthex.c
index c652f6a..3a32003 100644
--- a/source/components/utilities/uthex.c
+++ b/source/components/utilities/uthex.c
@@ -122,7 +122,7 @@
/* Hex to ASCII conversion table */
-static char AcpiGbl_HexToAscii[] =
+static const char AcpiGbl_HexToAscii[] =
{
'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'
};
diff --git a/source/include/acutils.h b/source/include/acutils.h
index 4fc44ff..f9372a2 100644
--- a/source/include/acutils.h
+++ b/source/include/acutils.h
@@ -278,7 +278,7 @@ AcpiUtInitGlobals (
#if defined(ACPI_DEBUG_OUTPUT) || defined(ACPI_DEBUGGER)
-char *
+const char *
AcpiUtGetMutexName (
UINT32 MutexId);
@@ -288,15 +288,15 @@ AcpiUtGetNotifyName (
ACPI_OBJECT_TYPE Type);
#endif
-char *
+const char *
AcpiUtGetTypeName (
ACPI_OBJECT_TYPE Type);
-char *
+const char *
AcpiUtGetNodeName (
void *Object);
-char *
+const char *
AcpiUtGetDescriptorName (
void *Object);
@@ -304,15 +304,15 @@ const char *
AcpiUtGetReferenceName (
ACPI_OPERAND_OBJECT *Object);
-char *
+const char *
AcpiUtGetObjectTypeName (
ACPI_OPERAND_OBJECT *ObjDesc);
-char *
+const char *
AcpiUtGetRegionName (
UINT8 SpaceId);
-char *
+const char *
AcpiUtGetEventName (
UINT32 EventId);
--
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