On 25.05.2023 18:11, Fangrui Song wrote: > On 2023-05-25, Jan Beulich wrote: >> On 25.05.2023 17:16, Fangrui Song wrote: >>> --- a/gcc/doc/invoke.texi >>> +++ b/gcc/doc/invoke.texi >>> @@ -32942,9 +32942,10 @@ the cache line size. @samp{compat} is the default. >>> >>> @opindex mlarge-data-threshold >>> @item -mlarge-data-threshold=@var{threshold} >>> -When @option{-mcmodel=medium} is specified, data objects larger than >>> -@var{threshold} are placed in the large data section. This value must be >>> the >>> -same across all objects linked into the binary, and defaults to 65535. >>> +When @option{-mcmodel=medium} or @option{-mcmodel=large} is specified, data >>> +objects larger than @var{threshold} are placed in large data sections. >>> This >>> +value must be the same across all objects linked into the binary, and >>> defaults >>> +to 65535. >> >> Where's the "must be the same" requirement coming from? > > It's an existing requirement. I think it may be related to discouraging > different COMDAT sections names due to different -mlarge-data-threshold=. > I don't think it makes sense but did not feel strongly dropping it. > > Happy to drop the requirement if I revise this patch.
I understand that this isn't something you introduce, but it still stuck me as odd. Therefore I thought I'd suggest to take the opportunity to at least soften the language, unless of course there's a real reason behind it. >> As to the default - to remain compatible with earlier versions, shouldn't >> large model code default to "infinity"? >> >> Jan > > I have thought about this compatibility need and feel that it is very > unlikly to be needed. GNU ld has supported large data sections since > 2005 > (https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=3b22753a67cf616514de804ef6d5ed5e90a7d883). > Users' programs with the internal linker scripts will still be working > and -fdata-sections sections will be combined. Well, the concern clearly is about custom scripts. Imo ... > First, -mcmodel=large use cases are rare enough. Rare perhaps > -mcmodel=largel was considered theoretic excercise in > trying to reach feature completion > (https://groups.google.com/g/x86-64-abi/c/jnQdJeabxiU/m/NNuA0P7pAQAJ), > without this patch -mcmodel=large object files don't interract well with > existing -mcmodel=small object files. ... the more exotic a project, the more likely it is that they're using custom scripts. > Moreover, if a user expects a specific section prefix with > -mcmodel=large, that's a brittle assumption. I think it's fair to say > that the fault is on the user side and GCC doesn't need to work around > their issues. I guess I don't really see what you base this on. Without any special options, expecting data to end up in .data/.bss/.rodata (and variants thereof) looks like quite reasonable an assumption to me. Jan