Re: i370 port - constructing compile script

["Paul Edwards" <mutazilah@gmail.com>]

Hi Ian, thanks for your reply.

>> 1. First I need to use my current build machine, Linux,
>> to first of all convert the i370.md into insn*.c files, then
>> generate an xgcc.  The xgcc would be capable of producing
>> i370 code so long as I use the "-S" option.  It doesn't really
>> matter how this xgcc was created (ie using non-C90
>> stuff like fork available on my build machine).
>>
>> 2. It is now (at the Alaskan stage) that I need a different sort
>> of config.h/auto-host.h that excludes things like fork.  I can
>> present my i370 include files here, that only include C90
>> functions.  It is at this stage that I need it to invoke xgcc
>> (still on the build machine), but it will be with the -S option,
>> so there will be no .o files (although I could perhaps fake
>> that via a scipt to keep "make" happy) and no executable
>> built.  The "fake" script could generate JCL at the same time.
>> The C90 library (for MVS) also needs to be cross-compiled
>> here.
>>
>> 3. Then I need to assemble all the assembler on real i370
>> (MVS).  It is at this point that a real host (ie on i370 MVS)
>> xgcc is built.
>>
>> 4. Then I can use that xgcc (on MVS) to compile arbitary
>> C programs.  Technically I could have had a requirement
>> for this i370-mvs host compiler to produce say sparc target
>> code.
>
> What most people do is:
>
> * Configure gcc as a cross-compiler.

So this would not be considered a Canadian Cross after all,
and with configure I only change the target, not the host?

> * Write a cross-assembler and cross-linker.

Sure, and that's what I'm trying to avoid.  I have a perfectly working
assembler and linker on MVS already.  It's been working for several
decades.

> * Copy header files and libraries from the host (MVS).

That's fine.  And use the --with-root option of configure to get
them used?

> Now you have a complete cross-toolchain running on a supported host
> which can produce executables which run on MVS.

It's a can of worms just trying to copy MVS load modules.  There's
meta-data in 2 different places and it needs to be packaged.

> * Use that cross-toolchain to build a version of gcc which runs on
>  MVS.  At this step you port gcc to work on MVS.
> * Run that gcc on MVS.
>
> (Note that you mention fork, but as you probably know the gcc code
> never actually calls fork.  It calls the pexecute routines in
> libiberty.  Those routines have been ported to several different
> hosts, including MS-DOS.  If you port them to MVS, then you don't have
> to worry about fork.)

I spent several minutes going through the config.h looking at the
"detected" functions to find a good example.  Maybe I should I
have getrlimit or getrusage or fputs_unlocked instead.

>> To fit into the standard Canadian Cross 3-step model, I need
>> to either collapse steps 2 and 3 into 1 theoretical step, executed
>> across 2 platforms (compile on one, assemble on another),
>
> Right, people normally do this by using a cross-assembler and
> cross-linker.

Ok.

>> I suspect that it will only take 20 lines or similar of intrusive
>> Makefile/shell script changes to shoe-horn my way into the
>> existing gcc methodology.  All I need to do is force it to use
>> my C90 headers at the right spot, so that it stops thinking
>> that I have fork etc, and stop it trying to build an executable.
>>
>> Can someone tell me where to put those 20 lines?
>
> One way to shoe-horn those lines in would be to make your
> cross-assembler and cross-linker actually be shell scripts.

Ok, that's no problem.

> They
> would copy the files to MVS, run the real assembler and linker, and
> copy the output back.

I might theoretically be able to do such a thing, but that's not what I'm
after.  I'm just after 200+ assembler files to be produced so that I can
zip them up and take them to a real MVS site or whatever to get
compiled.  It looks like someone just wrote a C compiler in
370 assembler, which is now all natural MVS (the objective of the
exercise).

> That would be more than 20 lines, but it seems
> doable to me.

Actually, that would be 0 lines of intrusive code (ie changing GCC
itself).

> But I don't understand the bit about C90 headers.  gcc doesn't need
> fork, but it does need a way to execute other programs.

No, I use intrusive code to convert the pexecute call into a static
call to cc1 (effectively - I actually intercept it within gcc itself, see
below).  And that is why I need a Makefile target that includes
all the object code.  Because I compile the 450,000 lines of C code
into 850,000 lines of assembler code to produce a 3.4 MB gcc load
module for MVS.  Those figures are from gcc 3.4.6.

BFN.  Paul.




***************
*** 2610,2615 ****
--- 2623,2631 ----
  static int
  execute (void)
  {
+ #ifdef SINGLE_EXECUTABLE
+   int ret_code = 0;
+ #endif
    int i;
    int n_commands;             /* # of command.  */
    char *string;
***************
*** 2756,2761 ****
--- 2772,2792 ----
        char *errmsg_fmt, *errmsg_arg;
        const char *string = commands[i].argv[0];

+ #ifdef SINGLE_EXECUTABLE
+      {
+          int cnt = 0;
+
+          while (commands[i].argv[cnt] != NULL)
+          {
+              cnt++;
+          }
+          if (strcmp(string, "cc1") == 0)
+          {
+              ret_code = toplev_main(cnt, commands[i].argv);
+              if (ret_code != 0) break;
+          }
+       }
+ #else
        /* For some bizarre reason, the second argument of execvp() is
         char *const *, not const char *const *.  */
        commands[i].pid = pexecute (string, (char *const *) 
commands[i].argv,