Hi Honza, > On 8 Jul 2025, at 10:31 pm, Jan Hubicka <hubi...@ucw.cz> wrote: > > External email: Use caution opening links or attachments > > >> Hi Honza, >> >>> On 8 Jul 2025, at 2:26 am, Jan Hubicka <hubi...@ucw.cz> wrote: >>> >>> External email: Use caution opening links or attachments >>> >>> >>> Hi, >>> as discussed also on the autofdo pull request, LLVM solves the same >>> problem using -funique-internal-linkage-names >>> https://reviews.llvm.org/D73307 >>> >>> All non-public functions gets theis symbol renamed from >>> <function_name>.__uniq.<md5 sum of source file name in decadic> >> >> How is __uniq.<md5 sum of source file name in decadic> added to static >> symbols in the profile? > > The patch does three things > 1) extends ipa-visibility pass to rename all non-public function > symbols adding the __uniq suffix. > This skips those marked as used so asm statements can work. > 2) makes dwarf2out to always add DW_AT_linkage_name attribute to > inlined to DW_TAG_inlined_subroutine dies > 3) extends auto-profile to accept profiles with unique names > when building without unique names and vice versa. > > I think it is pretty much what LLVM does except that I compute hash > based on object file name while LLVM uses filename of the outer > translation unit (which is easy to change, I just wanted to have > something functional to see how it works in practice). > > There is a comment on the pull request comment I added > https://github.com/google/autofdo/pull/244#issuecomment-3046121191 > So it seems that llvm folks are not that happy with uniq suffixes since > it breaks asm statements in Linux kernel. I originally tought renaming > is done in dwarf only but indeed renaming all static symbols is quite > radical. > > Their proposal > https://discourse.llvm.org/t/rfc-keep-globalvalue-guids-stable/84801 > seems to be equivalent to what we have as profile_id. It is 64bit > identifier of a function that should be stable across builds and (modulo > conflits) unique within translated program. Currently it is assigned > only to functions that may be used as indirect call targets and is used > by normal FDO for resolving cross-unit indirect calls. > > One option would be to use profile IDs in auto-profiles too. I guess > they can be streamed to dwarf via an extension as 64bit IDs. But it is > not clear to me that it is what LLVM folks work on and if it will > eventually get upstreamed. > > If we want to finish your solution (adding file names in create_gcov). I > think we need to solve the following: > 1) extend dwarf2out to add DW_AT_linkage_name attributes for all > function symbols. This is easy to do. > 2) veirfy that create_gcov can safely determine symbols with public > or static linkage (even inlined ones). There is DW_AT_public > attribute > and stream file names only for public linkage symbols > 3) instead of streaming filename of file containing the symbol > stream filename of the corresponding translation unit. > > I would say that the advantage of profile id is probably shorter gcov > files, advantage of streaming filename:symbol_name pairs is that the > profile info is easier to read. What do you think?
Thanks for the clarification. Since LLVM has been using __uniq suffix and this is optional (controlled by flag), IMO we could go with your patch. Thanks, Kugan > > Honza
