cminusminus.org does not have a link to the spec

[Simon Peyton Jones]

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.

Simon

| -----Original Message-----
| From: Sergei Trofimovich [mailto:slyich at 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 <simonpj at 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:slyich at 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
| 
| 
| --
| 
|   Sergei