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@xxxxxxxxxx>
>
> Cc: stable@xxxxxxxxxxxxxxx
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
