[ECOS] ecosSWtools problems

[ECOS] ecosSWtools problems

[Robin Farine]

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Hi,

This posting does not concern ecos directly but it may help some ecos
users, so ...

1. When linking code with PC REL24 branches, the ARM bfd linker does not
   complain nor modify the branch instruction when the offset overflows,
   it just generates code that branch anywhere. The attached patch
   should fix this problem.

2. The '--gc-sections' linker flag causes the linker to discard
   referenced code.  For instance:

        class A { public: virtual void f(int) = 0; };

        class B : public A { public: void f(int); };

        void B::f(int) { ...  }

        A &a = make_B_instance();

        a.f();

   In this case, the linker garbage-collects B's vtable entry for 'f()'
   and then discard B::f(). The assembler code gcc produces, in
   particular '.vtable_inherit #__vt_1B, #0', implies that the linker
   will neither propagate the mark of A::f() to B::f(), nor will it use
   shared vtable marks.

   But when B inherits virtually from A, then gcc generates a
   '.vtable_inherit #__vt_1B, #__vt_1A'.

   I tried this with the 'ecosSWtools-arm-990321' and with
   gcc-2.95. Both result in the same problem.

   Now, my questions:
    - did I miss something?
    - if not then I think that gcc is the culprit since
      '.vtable_inherit' does not have anything to do with virtual
      inheritance, right?

Thanks,

Robin
-- 
Robin Farine
ACN Advanced Communications Networks SA   Tel: +41 32 724 74 34
Rue du Puits-Godet 8a                     FAX: +41 32 724 74 54
CH-2000 Neuchâtel                      e-mail: robin.farine@terminus.org

[ECOS] ecosSWtools problems.2

[Robin Farine]

Hi,

Sorry, yesterday I forgot to include the mentioned BFD fix in my posting ...

Robin

----------- cut here --------------

*** ecosSWtools-arm-990321.orig/src/bfd/elf32-arm.h     Fri May  7 16:35:05 1999
--- ecosSWtools-arm-990321/src/bfd/elf32-arm.h  Sat Aug  7 13:46:00 1999
***************
*** 913,917 ****
                + input_section->output_offset + 8);
        value -= offset;
!       value = value >> howto->rightshift;
  
        value &= 0xffffff;
--- 913,920 ----
                + input_section->output_offset + 8);
        value -= offset;
!       value = (bfd_signed_vma)value >> howto->rightshift;
!       if ((bfd_signed_vma) value > 0x7fffff ||
!         (bfd_signed_vma) value < -0x800000)
!       return bfd_reloc_overflow;
  
        value &= 0xffffff;

Re: [ECOS] ecosSWtools problems

[Bart Veer]

>>>>> "Robin" == Robin Farine <advanc@dial.eunet.ch> writes:

    Robin> Hi, This posting does not concern ecos directly but it may
    Robin> help some ecos users, so ...

    Robin> 1. When linking code with PC REL24 branches, the ARM bfd
    Robin> linker does not complain nor modify the branch instruction
    Robin> when the offset overflows, it just generates code that
    Robin> branch anywhere. The attached patch should fix this
    Robin> problem.

I passed this on to the gcc team, and the patch has been incorporated
into the master binutils sources (with a few minor changes). I have
also listed the problem and the patch on the known problems list,
http://sourceware.cygnus.com/problemlist.html . Thanks!

    Robin> 2. The '--gc-sections' linker flag causes the linker to
    Robin> discard referenced code. For instance:

    <snip>

    Robin>    Now, my questions:
    Robin>     - did I miss something?
    Robin>     - if not then I think that gcc is the culprit since
    Robin>       '.vtable_inherit' does not have anything to do with virtual
    Robin>       inheritance, right?

This one has also been passed on to the gcc team for comments. 

Bart Veer // eCos net maintainer