[v2] iw: set retain atrribute on sections

Message ID 20210426163021.3594482-1-manojgupta@google.com
State New
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  • [v2] iw: set retain atrribute on sections
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Commit Message

Manoj Gupta April 26, 2021, 4:30 p.m.
LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage
collection of C identifier name sections despite the __start_/__stop_
references.  Simply set the retain attribute so that GCC 11 (if
configure-time binutils is 2.36 or newer)/Clang 13 will set the
SHF_GNU_RETAIN section attribute to prevent garbage collection.

Without the patch, there are linker errors like the following with -z
start-stop-gc:
ld.lld: error: undefined symbol: __stop___cmd
>>> referenced by iw.c:418
>>>               iw.o:(__handle_cmd)

Suggested-by: Fangrui Song <maskray@google.com>

Cc: stable@vger.kernel.org

Signed-off-by: Manoj Gupta <manojgupta@google.com>
---
Changes v1 -> v2:
Apply the retain attribute to all places with attribute used.

 iw.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Comments

Brian Norris April 29, 2021, 5:59 p.m. | #1
(removing stable@vger.kernel.org from CC)

On Mon, Apr 26, 2021 at 9:30 AM Manoj Gupta <manojgupta@google.com> wrote:
>

> LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage

> collection of C identifier name sections despite the __start_/__stop_

> references.  Simply set the retain attribute so that GCC 11 (if

> configure-time binutils is 2.36 or newer)/Clang 13 will set the

> SHF_GNU_RETAIN section attribute to prevent garbage collection.

>

> Without the patch, there are linker errors like the following with -z

> start-stop-gc:

> ld.lld: error: undefined symbol: __stop___cmd

> >>> referenced by iw.c:418

> >>>               iw.o:(__handle_cmd)

>

> Suggested-by: Fangrui Song <maskray@google.com>

>

> Cc: stable@vger.kernel.org

>

> Signed-off-by: Manoj Gupta <manojgupta@google.com>


This is not a kernel patch and so should not be sent to the
linux-stable list. I think Greg KH's bot already told you as much on
earlier versions.

See:
https://git.kernel.org/pub/scm/linux/kernel/git/jberg/iw.git/tree/README

"Please send all patches to Johannes Berg <johannes@sipsolutions.net>
and CC linux-wireless@vger.kernel.org for community review."

You're ~close.

Brian
Johannes Berg May 31, 2021, 7:33 p.m. | #2
On Mon, 2021-04-26 at 09:30 -0700, Manoj Gupta wrote:
> LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage

> collection of C identifier name sections despite the __start_/__stop_

> references.  Simply set the retain attribute so that GCC 11 (if

> configure-time binutils is 2.36 or newer)/Clang 13 will set the

> SHF_GNU_RETAIN section attribute to prevent garbage collection.

> 

> Without the patch, there are linker errors like the following with -z

> start-stop-gc:

> ld.lld: error: undefined symbol: __stop___cmd

> > > > referenced by iw.c:418

> > > >               iw.o:(__handle_cmd)

> 

> Suggested-by: Fangrui Song <maskray@google.com>

> 

> Cc: stable@vger.kernel.org


This is *clearly* inappropriate.

> +++ b/iw.h

> @@ -118,8 +118,9 @@ struct chandef {

>  		.parent = _section,					\

>  		.selector = (_sel),					\

>  	};								\

> +	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\

>  	static struct cmd *__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden ## _p \

> -	__attribute__((used,section("__cmd"))) =			\

> +	__attribute__((used,retain,section("__cmd"))) =			\

>  	&__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden

>  #define __ACMD(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel, _alias)\

>  	__COMMAND(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel);\

> @@ -141,16 +142,18 @@ struct chandef {

>  		.handler = (_handler),					\

>  		.help = (_help),					\

>  	 };								\

> +	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\

>  	static struct cmd *__section ## _ ## _name ## _p		\

> -	__attribute__((used,section("__cmd"))) = &__section ## _ ## _name

> +	__attribute__((used,retain,section("__cmd"))) = &__section ## _ ## _name


All of these cases are in macros, it feels it would be more appropriate
to do _Pragma("GCC diagnostic push") and ...pop... around it?

johannes

Patch

diff --git a/iw.h b/iw.h
index 7f7f4fc..8ca8e44 100644
--- a/iw.h
+++ b/iw.h
@@ -118,8 +118,9 @@  struct chandef {
 		.parent = _section,					\
 		.selector = (_sel),					\
 	};								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden ## _p \
-	__attribute__((used,section("__cmd"))) =			\
+	__attribute__((used,retain,section("__cmd"))) =			\
 	&__cmd ## _ ## _symname ## _ ## _handler ## _ ## _nlcmd ## _ ## _idby ## _ ## _hidden
 #define __ACMD(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel, _alias)\
 	__COMMAND(_section, _symname, _name, _args, _nlcmd, _flags, _hidden, _idby, _handler, _help, _sel);\
@@ -141,16 +142,18 @@  struct chandef {
 		.handler = (_handler),					\
 		.help = (_help),					\
 	 };								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__section ## _ ## _name ## _p		\
-	__attribute__((used,section("__cmd"))) = &__section ## _ ## _name
+	__attribute__((used,retain,section("__cmd"))) = &__section ## _ ## _name
 
 #define SECTION(_name)							\
 	struct cmd __section ## _ ## _name = {				\
 		.name = (#_name),					\
 		.hidden = 1,						\
 	};								\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	static struct cmd *__section ## _ ## _name ## _p		\
-	__attribute__((used,section("__cmd"))) = &__section ## _ ## _name
+	__attribute__((used,retain,section("__cmd"))) = &__section ## _ ## _name
 
 #define DECLARE_SECTION(_name)						\
 	extern struct cmd __section ## _ ## _name;
@@ -162,13 +165,14 @@  struct vendor_event {
 };
 
 #define VENDOR_EVENT(_id, _subcmd, _callback)				\
+	_Pragma("GCC diagnostic ignored \"-Wattributes\"") 		\
 	const struct vendor_event 					\
 	vendor_event_ ## _id ## _ ## _subcmd = {			\
 		.vendor_id = _id,					\
 		.subcmd = _subcmd,					\
 		.callback = _callback,					\
 	}, * const vendor_event_ ## _id ## _ ## _subcmd ## _p		\
-	__attribute__((used,section("vendor_event"))) =			\
+	__attribute__((used,retain,section("vendor_event"))) =			\
 		&vendor_event_ ## _id ## _ ## _subcmd
 
 extern const char iw_version[];