Re: PING: PATCH: PR target/46770: Use .init_array/.fini_array sections

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Jul 22, 2011 at 5:30 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Fri, Jul 22, 2011 at 04:59:28AM -0700, H.J. Lu wrote:
>> @@ -2660,6 +2664,7 @@ esac
>> ?case ${target} in
>> ?i[34567]86-*-linux* | x86_64-*-linux*)
>> ? ? ? tmake_file="${tmake_file} i386/t-pmm_malloc i386/t-i386"
>> + ? ? use_initfini_array=yes
>> ? ? ? ;;
>> ?i[34567]86-*-* | x86_64-*-*)
>> ? ? ? tmake_file="${tmake_file} i386/t-gmm_malloc i386/t-i386"
>
> What is i?86/x86_64 specific on it? ?Don't most other glibc targets
> want to use it too, perhaps with some arch specific tweaks?

I do have a patch for all ELF targets:

http://gcc.gnu.org/ml/gcc-patches/2011-06/msg01416.html

It touches many targets. .  But I only have one feedback from one
target maintainer.  I don't know how long it will take to review it.


>> --- /dev/null
>> +++ b/gcc/config/initfini-array.c
>
> This is ugly. ?varasm.c already has lots of ELF specific code, simply
> put them there as well and only let configury set some macro which will
> allow targets to choose which of the implementations in the generic code
> they want to use (or if they want their own which e.g. calls the generic
> routine and does something additional to it etc.). ?The sections probably
> can be created only the first time you actually need them.

I will do that.

>> --- a/gcc/crtstuff.c
>> +++ b/gcc/crtstuff.c
>> @@ -189,6 +190,9 @@ typedef void (*func_ptr) (void);
>> ? ? refer to only the __CTOR_END__ symbol in crtend.o and the __DTOR_LIST__
>> ? ? symbol in crtbegin.o, where they are defined. ?*/
>>
>> +/* No need for .ctors/.dtors section if linker can place them in
>> + ? .init_array/.fini_array section. ?*/
>> +#ifndef NO_CTORS_DTORS_SECTIONS
>> ?/* The -1 is a flag to __do_global_[cd]tors indicating that this table
>> ? ? does not start with a count of elements. ?*/
>> ?#ifdef CTOR_LIST_BEGIN
>> @@ -219,6 +223,7 @@ STATIC func_ptr __DTOR_LIST__[1]
>> ? ?__attribute__((section(".dtors"), aligned(sizeof(func_ptr))))
>> ? ?= { (func_ptr) (-1) };
>> ?#endif /* __DTOR_LIST__ alternatives */
>> +#endif /* NO_CTORS_DTORS_SECTIONS */
>>
>> ?#ifdef USE_EH_FRAME_REGISTRY
>> ?/* Stick a label at the beginning of the frame unwind info so we can register
>> @@ -489,6 +494,9 @@ __do_global_ctors_1(void)
>>
>> ?#elif defined(CRT_END) /* ! CRT_BEGIN */
>>
>> +/* No need for .ctors/.dtors section if linker can place them in
>> + ? .init_array/.fini_array section. ?*/
>> +#ifndef NO_CTORS_DTORS_SECTIONS
>> ?/* Put a word containing zero at the end of each of our two lists of function
>> ? ? addresses. ?Note that the words defined here go into the .ctors and .dtors
>> ? ? sections of the crtend.o file, and since that file is always linked in
>> @@ -534,6 +542,7 @@ STATIC func_ptr __DTOR_END__[1]
>> ? ?__attribute__((used, section(".dtors"), aligned(sizeof(func_ptr))))
>> ? ?= { (func_ptr) 0 };
>> ?#endif
>> +#endif /* NO_CTORS_DTORS_SECTIONS */
>>
>> ?#ifdef EH_FRAME_SECTION_NAME
>> ?/* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
>
> I don't see how you can do this. ?It would IMO break any time you link code
> built by different gcc versions where some code emitted by the older gcc
> used .ctors or .dtors.

crtstuff.c is used to generate crt*.o, which is the part of GCC.  You only use
it with the GCC you are using.  Since your GCC doesn't put anything in
.ctors/.dtors section, you don't need them.  As for .o files generated by
old GCCs, that is the linker test, use_initfini_array, is for.  The newer linker
can put input .ctors/.dtors sections in output .init_array/,fini_array sections.


-- 
H.J.