On 10/17/19 7:59 PM, Nick Alcock wrote: > On 17 Oct 2019, Richard Biener verbalised: > >> On Thu, Oct 17, 2019 at 7:36 PM Nick Alcock <nick.alc...@oracle.com> wrote: >>> >>> On 11 Oct 2019, Indu Bhagat stated: >>>> Compile with -g -gdwarf-like-ctf and use dwz -o <binary_dwz> <binary> >>>> (using >>>> dwz compiled from the master branch) on the generated binaries: >>>> >>>> (coreutils-0.22) >>>> .debug_info(D1) | .debug_abbrev(D2) | .debug_str(D4) | .ctf >>>> (uncompressed) | ratio (.ctf/(D1+D2+0.5*D4)) >>>> ls 30616 | 1136 | 21098 | 26240 >>>> | 0.62 >>>> pwd 10734 | 788 | 10433 | 13929 >>>> | 0.83 >>>> groups 10706 | 811 | 10249 | 13378 >>>> | 0.80 >>>> >>>> (emacs-26.3) >>>> .debug_info(D1) | .debug_abbrev(D2) | .debug_str(D4) | .ctf >>>> (uncompressed) | ratio (.ctf/(D1+D2+0.5*D4)) >>>> emacs-26.3.1 674657 | 6402 | 273963 | 273910 >>>> | 0.33 >> >> Btw, for a fair comparison you have to remove all DW_TAG_subroutine >> children as well since CTF doesn't represent scopes or local variables >> at all (nor types only used by locals). It seems CTF only represents >> function entry points. > > Good point: I'll have to hack up a DWARF trimmer to do this comparison > properly, I think. (Though CTF does represent global variables, > including file-scope statics.)
Wouldn't it be possible to extend the -gdwarf-like-ctf hack to skip emitting those things? > > In most cases local types etc are a fairly small contributor to the > total volume -- but macros can contribute a lot in some codebases. (The > Linux kernel's READ_ONCE macro is one I've personally been bitten by in > the past, with a new local struct in every use. GCC doesn't deduplicate > any of those so the resulting bloat from tens of thousands of instances > of this identical structure is quite incredible...) > Sounds like something that would be beneficial to do with DWARF too. Thanks, Pedro Alves
