Re: [PATCH] [libstdc++] introduce --disable-compat-libstdcxx-abi

[Alexandre Oliva <oliva@adacore.com>]

On Apr 16, 2024, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

>> +dnl
>> +dnl Enable -Wabi=2 if not overridden by --disable-compat-libstdcxx-abi.
>> +dnl
>> +AC_DEFUN([GLIBCXX_ENABLE_WABI], [
>> +  # Default.
>> +  WARN_FLAGS_WABI=\ -Wabi=2
>> +  AC_MSG_CHECKING([for --disable-compat-libstdcxx-abi])
>> +  AC_ARG_ENABLE([compat-libstdcxx-abi],

> We have the GLIBCXX_ENABLE macro to simplify creating new --enable options.

*nod*.  There was some reason why I didn't use it at first.  Maybe it
can be used with the patch as it ended up.  Will revisit.

>> +    AC_HELP_STRING([--disable-compat-libstdcxx-abi],
>> +                  [Disable backward-compatibility ABI symbols)]),

> There's a stray ')' here.

Ugh, thanks

>> --- a/libstdc++-v3/doc/html/manual/configure.html
>> +++ b/libstdc++-v3/doc/html/manual/configure.html

> This should be in doc/xml/manual/configure.xml too, which is used to
> generate the HTML using docbook.

Oh, right.  Doh.  So much for grepping for an existing option and
jumping to edit the first match :-)

> The description here in the docs (and the name of the configure
> option) seem much too vague. Libstdc++ has dozens, probably hundreds,
> of "backward-compatibility ABI symbols", and this only affects touches
> a tiny handful of them. Just the aliases created automatically by the
> compiler for mangling changes, right?

Yeah.

I had used --disable-libstdcxx-Wabi at some point, maybe that's better.


FTR, we now have a binutils patch (thanks H.J.Lu) to address the
underlying problem, so we'll probably no longer need the workaround that
led me to propose this change.  I wonder if there's interest in keeping
it.  I'd be equally happy to make the adjustments, or to withdraw it (or
pretty much anything in between ;-).  WDYT?

-- 
Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
   Free Software Activist                   GNU Toolchain Engineer
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