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.
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. 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. 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.
