Re: [patch] Fix EH breakage in LTO mode

[Richard Biener <richard.guenther@gmail.com>]

On November 9, 2017 5:11:39 PM GMT+01:00, Eric Botcazou <ebotcazou@adacore.com> wrote:
>Hi,
>
>the patch
>
>2017-07-06  Jan Hubicka  <hubicka@ucw.cz>
>
>	* lto-wrapper.c (merge_and_complain): Do not merge
>	fexceptions, fnon_call_exceptions, ftrapv, ffp_contract_, fmath_errno,
>	fsigned_zeros, ftrapping_math, fwrapv.
>	(append_compiler_options): Do not track these options.
>	(append_linker_options): Likewie
>
>has broken exception handling in LTO mode for targets which don't force
>either 
>-funwind-tables or -fasynchronous-unwind-tables (i.e not x86) and do
>not 
>default to -fdwarf2-cfi-asm (i.e. not Linux), for example
>SPARC/Solaris.
>
>The problem is that the eh_frame section is no longer generated because
>it is 
>emitted from compile_file:
>
>    #if defined DWARF2_DEBUGGING_INFO || defined DWARF2_UNWIND_INFO
>      if (dwarf2out_do_frame ())
>	dwarf2out_frame_finish ();
>    #endif
>
>and this requires that either flag_unwind_tables or flag_exceptions be
>set.
>
>But both -funwind-tables and -fexceptions are optimization options
>defaulting 
>to 0 and they are reset to 0 through optimization_default_node after
>the last 
>function is processed by the cgraph machinery.
>
>Note that flag_exceptions is generally set to 1 in lto_init_eh very
>early, but 
>the above mechanism overrides it.  However, flag_exceptions may *never*
>be set 
>to 1 for a specific partition if it contains only EH-neutral functions;
>that's 
>why I think that there is no other way than restoring the build-wide
>handling 
>of -fexceptions before Jan's patch (hopefully it's the only affected
>switch).
>
>Tested (lightly for now) on x86-64/Linux and SPARC/Solaris, OK for
>mainline?

OK. 

Richard. 

>
>2017-11-09  Eric Botcazou  <ebotcazou@adacore.com>
>
>	* lto-opts.c (lto_write_options): Do not save -fnon-call-exceptions,
>	-ffp-contract, -fmath-errno, -fsigned-zeros, -ftrapping-math, -ftrapv
>	and -fwrapv.
>	* lto-wrapper.c (merge_and_complain): Merge again -fexceptions.
>	(append_compiler_options): Pass again -fexceptions.