[RFC PATCH] Implementing ifunc target hook

[Maxim Kuvyrkov]

On 10/01/2013, at 12:24 AM, Alexander Ivchenko wrote:

>> Config/linux-android.h is a better place for this declaration.

I was wrong here.  Config/linux-android.h is not a "re-includable" header, and is not fit for function declarations.

> 
> That wouldn't help, I got the following error:
> 
> In file included from ../../.././gcc/tm.h:24:0,
>                 from [..]/src/gcc/libgcc/generic-morestack-thread.c:29:
> [..]/src/gcc/libgcc/../gcc/config/linux-android.h:62:1: error: unknown
> type name ‘bool’
> extern bool linux_android_has_ifunc_p (void);
> ^
> 
> Anyway, linux-protos.h looks to me as a good thing to have (e.g. for
> libc_has_function hook, that is
> supposed to be commited in a near future) for declaring linux (and
> Android) specific versions of hooks..

OK, I agree.  In theory linux_android_has_ifunc_p could've been placed into linux-android-protos.h, but having a separate file (from linux-protos.h) just for 1-2 declarations is not justified.
 
>>> + "It returns true if the target supports GNU indirect functions.\n\
>>> +The support includes the assembler, linker and dynamic linker.\n\
>>> +The default value of this hook is defined as for the host machine.",
>> 
>> Are your sure the last sentence is correct?  It seems the default value for this hook is based on which libc is being used.  Maybe it would be more accurate to say "The default value of this hook is based on target's libc."?
> 
> Well yes, you are right that the default value depends on version of
> libc, but this version
> is checked on the configure time for the host machine
> (HAVE_GNU_INDIRECT_FUNCTION),

No.  And even if that was the case that would be a bug.

HAVE_GNU_INDIRECT_FUNCTION is set based on default_gnu_indirect_function variable defined in config.gcc (unless overridden with a configure argument).  This variable is set to true for targets that support IFUNCs irrespective of host and host's libc.

> --- a/gcc/config.gcc
> +++ b/gcc/config.gcc
> @@ -637,6 +637,11 @@ case ${target} in
>        native_system_header_dir=/include
>        ;;
>    esac
> +  case $target in
> +    *linux*)
> +      tm_p_file="${tm_p_file} linux-protos.h"
> +      ;;
> +  esac
>    # glibc / uclibc / bionic switch.
>    # uclibc and bionic aren't usable for GNU/Hurd and neither for GNU/k*BSD.
>    case $target in
> @@ -662,8 +667,10 @@ case ${target} in
>    # Add Android userspace support to Linux targets.
>    case $target in
>      *linux*)
> +      tmake_file="${tmake_file} t-linux-android"
>        tm_file="$tm_file linux-android.h"
>        extra_options="$extra_options linux-android.opt"
> +      extra_objs="$extra_objs linux-android.o"
>        ;;
>    esac
>    # Enable compilation for Android by default for *android* targets.
> 

Also scan config.gcc for any other occurences of linux-android.h and add same changes there.  I believe only arm*-*-linux-* is affected.


> --- a/gcc/config/host-linux.c
> +++ b/gcc/config/host-linux.c
> @@ -23,7 +23,6 @@
>  #include "hosthooks.h"
>  #include "hosthooks-def.h"
>  
> -
>  /* Linux has a feature called exec-shield-randomize that perturbs the
>     address of non-fixed mapped segments by a (relatively) small amount.
>     The feature is intended to make it harder to attack the system with

Don't change formatting unless you are editing the code around it.

> diff --git a/gcc/config/linux-android.c b/gcc/config/linux-android.c
> new file mode 100644
> index 0000000..47cc50a
> --- /dev/null
> +++ b/gcc/config/linux-android.c
...
> +You should have received a copy of the GNU General Public License
> +along with GCC; see the file COPYING3.  If not see
> +<http://www.gnu.org/licenses/>.  */
> +
> +#include "config.h"
> +#include "system.h"
> +#include "coretypes.h"
> +#include "tm.h"

Add '#include "linux-protos.h"'.  Remember to update t-linux-android.

> +
> +/* Android does not support GNU indirect functions.  */
> +
> +bool
> +linux_android_has_ifunc_p (void)
> +{
> +  return TARGET_ANDROID ? false : HAVE_GNU_INDIRECT_FUNCTION;
> +}
> 


Please send one last version for the final review, primarily to double check your changes to arm*-linux-* to avoid breaking it.

Thanks!

--
Maxim Kuvyrkov