On Tue, 16 Sep 2014 20:23:10 +0000 Simon Peyton Jones <simo...@microsoft.com> 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:sly...@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 <simo...@microsoft.com> 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:sly...@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
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