Re: cminusminus.org does not have a link to the spec

On Tue, 16 Sep 2014 20:23:10 +0000 Simon Peyton Jones wrote:

Thanks. This is beyond my competence, and I'm totally submerged anyway. I suggest you make a Trac ticket about it anyway. Simon Marlow will probably have an opinion.

Today I've found an excuse to actually implement it :) https://phabricator.haskell.org/D622 Reused 'CLOSURE' token and added import CLOSURE id; to existing import id;

| -----Original Message----- | From: Sergei Trofimovich [mailto:slyich@gmail.com] | Sent: 16 September 2014 19:03 | To: Simon Peyton Jones | Cc: Norman Ramsey; ghc-devs; Simon Marlow | Subject: Re: cminusminus.org does not have a link to the spec | | On Mon, 15 Sep 2014 12:05:27 +0000 | Simon Peyton Jones wrote: | | My planned change is for GHC's .cmm files syntax/codegen. | The idea came out after having stumbled upon a rare ia64 | bug in GHC's C codegen: | | | http://git.haskell.org/ghc.git/commitdiff/e18525fae273f4c1ad8d6cbe1dea4fc | 074cac721 | | The fundamental bug here is the following: | Suppose we have two bits of rts: one .c file and one .cmm file | | // rts.c defines and exports a function and a variable | void some_rts_fun (void); | int some_rts_var; | | // rts.cmm uses rts.c's function and variable | import some_rts_fun; /* this forces C codegen to emit function-like | 'StgFunPtr some_rts_fun ();' | prototype, it's fine */ | | import some_rts_var; /* also forces C codegen to emit function-like | 'StgFunPtr some_rts_var ();' | prototype, it's broken */ | // ... | W whatever = &some_rts_var; /* will pick address not to a real | variable, but to a | so called | function stub, a separate structure | pointing to real | 'some_rts_var' */ | | I plan to tweak syntax to teach Cmm to distinct between | imported C global variables/constants, imported Cmm info | tables(closures), maybe other cases. | | I thought of adding haskell-like syntax for imports: | foreign ccall import some_rts_fun; | foreign cdata import some_rts_var; | | or maybe | import some_rts_fun; | import "&some_rts_fun" as some_rts_fun; | | This sort of bugs can be easily spotted by whole-program C compiler. | gcc can do it with -flto option. I basically added to the mk/build.mk: | SRC_CC_OPTS += -flto | SRC_LD_OPTS += -flto -fuse-linker-plugin | SRC_HC_OPTS += -optc-flto | SRC_HC_OPTS += -optl-flto -optl-fuse-linker-plugin | and started with './configure --enable-unregisterised' | | It immediately shown some of current offenders: | error: variable 'ghczmprim_GHCziTypes_False_closure' redeclared as | function | error: variable 'ghczmprim_GHCziTypes_True_closure' redeclared as | function | | I hope this fuzzy explanation makes some sense. | | Thanks! | | > Sergei | > | > C-- was originally envisaged as a target language for a variety of | compilers. But in fact LLVM, which was developed at a similar time, | "won" that race and has built a far larger ecosystem. That's fine with | us -- it's great how successful LLVM has been -- but it means that C-- is | now used essentially only in GHC. | > | > I'm not sure where the original C-- documents now are; Norman can you | say? (I do know that the cminusminus.org has lapsed.) | > | > The GHC variant of C-- is defined mainly by the Cmm data type in GHC's | source code. It does have a concrete syntax, because some bits of GHC's | runtime system are written in Cmm. But I fear that this concrete language | is not well documented. (Simon Marlow may know more here.) | > | > Because GHC's Cmm is part of GHC, we are free to change it. Would you | like to say more about the change you want to make, and why you want to | make it? Is this relating directly to GHC or to some other project? | > | > Simon | > | > | > | -----Original Message----- | > | From: Sergei Trofimovich [mailto:slyich@gmail.com] | > | Sent: 14 September 2014 17:16 | > | To: Simon Peyton Jones | > | Subject: cminusminus.org does not have a link to the spec | > | | > | Hello Simon! | > | | > | I had a plan to tweak a bit "import" statement | > | syntax of Cmm in GHC. | > | | > | Namely, to distinct between | > | import some_c_function; | > | import some_c_global_variable; | > | | > | To try it I first attempted to find latest c-- spec | > | (to find some design sketches if available) at | > | | > | http://www.cminusminus.org/c-downloads/ | > | | > | But seems the links (and images?) have gone away | > | as well as rsync server described at: | > | | > | http://www.cminusminus.org/the-c-rsync-server/ | > | | > | Maybe you could forward it to site admins so they would | > | tweak links or point me to working copy. | > | | > | Apologies for bothering you on such minor | > | | > | Thank you!

-- Sergei