https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82005
--- Comment #43 from Iain Sandoe <iains at gcc dot gnu.org> --- (In reply to Richard Biener from comment #42) > (In reply to Iain Sandoe from comment #40) > > Created attachment 44417 [details] > > Patch series to enable copying of early debug data. < snip> (not ignoring the other options - but let's look at the possibilities to do it a better way) > > - we seem to be jumping through quite a few hoops here, presumably because > > it's too complex to emit the relevant data as markup into the LTO stream > > directly? > > The issue is that we'd have to distribute _all_ early debug to _each_ > LTRANS unit with late debug. That's N-fold duplication that I wanted > to avoid... but yes, with the assembly scheme from above you could > "prepend" each LTRANS unit with the "merged" early debug assembly. > (at least N is limited by --param lto-partitions which defaults to 32...) hmm... > > Note that doing the assembling of the early debug during compile-time > and then have the linker at the final link pick up that debug from the > original objects as would have been my prefered way would be still the > best for compile-time and disk-space usage. But of course it wouldn't > work for DARWIN w/o assembler changes to support this kind of relocations. Darwin's assembler supports < undef symbol >+offset as a relocation. with "actual_target" the address we want "< undef symbol >" the LTO "_sinus.c.f4d7e603" type symbol we emit I'm not too well up on DWARF specifics, probably time to RTFM... is the intention of <undef symbol>+offset-Lcurrent_section_start a PC-rel form? (i.e. does the "offset" roll any more in than the actual_target-< undef symbol >)? Normally, as I noted above, Darwin does things like set $foo Ltarget_sym-Lcurrent_section_start .long $foo to render the inter-section-offset as an absolute value (i.e. eliding the reloc.) which dsymutil can understand because it knows the section starts already. ==== So .. if we can * copy the LTO early debug (renaming as now) * omit ld -r operation on these (which will just produce 0 output) * make the external refs into < undef symbol >+offset (where offset is actual_target-symbol) * defer the linking of the early debug copied objects until the final link. Then, since there will be references to the debug symbols in objects with non-zero text/data, presumably the linker has to honour those. (I don't know if it will, but it seems it should). this seems like something worth trying, before heading into the more complicated stuff. maybe I can fake the steps by hand and try it .. WDYT?
