LinuxLists.cc - [PATCH] iw: set retain atrribute on sections

2021-04-22 18:26:12

Subject: [PATCH] iw: set retain atrribute on sections

2021-04-23 07:44:39

Subject: Re: [PATCH] iw: set retain atrribute on sections

On Thu, Apr 22, 2021 at 11:25:45AM -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 <[email protected]>
>
> Signed-off-by: Manoj Gupta <[email protected]>
> ---
> iw.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

2021-04-24 00:32:56

by Manoj Gupta

[permalink] [raw]

Subject: [PATCH] iw: set retain atrribute on sections

2021-04-26 16:31:11

by Manoj Gupta

[permalink] [raw]

Subject: [PATCH v2] iw: set retain atrribute on sections

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 <[email protected]>

Cc: [email protected]

Signed-off-by: Manoj Gupta <[email protected]>
---
Changes v1 -> v2:
Apply the retain attribute to all places with attribute used.

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

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[];
--
2.31.1.498.g6c1eba8ee3d-goog

2021-04-29 18:00:56

by Brian Norris

[permalink] [raw]

Subject: Re: [PATCH v2] iw: set retain atrribute on sections

(removing [email protected] from CC)

On Mon, Apr 26, 2021 at 9:30 AM Manoj Gupta <[email protected]> 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 <[email protected]>
>
> Cc: [email protected]
>
> Signed-off-by: Manoj Gupta <[email protected]>

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 <[email protected]>
and CC [email protected] for community review."

You're ~close.

Brian

2021-05-31 19:37:01

by Johannes Berg

[permalink] [raw]

Subject: Re: [PATCH v2] iw: set retain atrribute on sections

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 <[email protected]>
>
> Cc: [email protected]

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