[m-rev.] for post-commit review: fix io section of transition guide

[Julien Fischer]

Hi Zoltan,

On Wed, 11 Feb 2015, Zoltan Somogyi wrote:

>
>
> On Wed, 11 Feb 2015 13:05:36 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
>> You seem to have committed another change along with this one
>> which adds MR_hash_string5, MR_hash_string6 etc.   This has
>> broken building of the stage2 library.
>
> That would be the change that Paul is looking at, whose
> log message and diff were posted as {Log,DIFF}.string_hash.
> I forgot that I "git add"ed the files in the same workspace
> without committing and pushing the commit.
>
> However, the diff was tested, and my bootcheck worked
> just fine. What kind of breakage are you experiencing?


When linking the stage 2 library:

....

ranlib -c   libmer_std.a
Undefined symbols for architecture x86_64:
   "_MR_hash_string5", referenced from:
       <predicate 'library.mercury_std_library_module'/1 mode 0> in
library.pic_o
       <predicate
'ops:ClassMethod_for_ops:op_table::ops:mercury_op_table:arity0:::ops.lookup_op_2_2_p'/0
mode 10001> in ops.pic_o
       <predicate
'ops:ClassMethod_for_ops:op_table::ops:mercury_op_table:arity0:::ops.lookup_op_infos_4_4_p'/0
mode 10001> in ops.pic_o
       <predicate
'ops:ClassMethod_for_ops:op_table::ops:mercury_op_table:arity0:::ops.lookup_op_infos_4'/4
mode 0> in ops.pic_o
       <predicate
'ops:ClassMethod_for_ops:op_table::ops:mercury_op_table:arity0:::ops.lookup_op_2'/2
mode 0> in ops.pic_o
       <predicate 'ops.lookup_mercury_postfix_op'/4 mode 0> in ops.pic_o
       <predicate 'ops.lookup_mercury_binary_prefix_op'/5 mode 0> in
ops.pic_o
       ...
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see
invocation)

Since there are separate versions of MR_hash_string5 and friends for GCC
and non-GCC, I suspect the issue is that the non-GCC version has not
been tested.

Aside: I haven't look at this in detail but it's possible clang could
also use the GCC definitions of these macros depeding on what GCC
extensions they make use of.

Cheers,
Julien.