Re: i370 port

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

> That depends a bit on the compiler version and optimization level,
> but (in particular in the 3.x time frame) GCC may output assembler
> code on a function-by-function basis, without necessarily reading
> in the whole source file first.

Ok, actually it doesn't matter if it doesn't work all the time.  I'll
always be compiling with -Os anyway, so it sounds like I'm in
with a chance of the whole file being read first?

If so, where is my first opportunity, in 3.2.3, to see if there's a
"main" function in this file?

>> > As crt0.o can be (and usually is) completely
>> > written in assembler, you can arrange for everything to be in the 
>> > sequence
>> > that is required.  (On the linker command line, crt0.o would be placed
>> > first, so if the entry point is the first thing in crt0.o it will then
>> > also be the first thing in the executable.)
>>
>> Yes, I can do that, but that means I need to have a linker command
>> line!  The way the MVS linker works, I can link my main program,
>> (which obviously doesn't have crt0 in it), and, thanks to the "END"
>> statement, I can specify an entry point.  This means no complaint
>> from the linker about a default (and wrong) entry point, and no
>> need for any linker statements.  It all automatically resolves.
>
> I don't know exactly how your port handles this on MVS, but usually
> GCC itself will invoke the linker, and will itself prepare an
> appropriate command linker for the linker.

GCC on MVS *only* outputs assembler.  ie you always have to
use the "-S" option.

By doing so, it turns GCC into a pure text-processing application,
which will thus work in any C90 environment.

> In current GCC, every insn contains "location" information pointing
> back to source code line (and column) numbers.  However, in GCC 3.x
> I think this wasn't yet present, but you had to rely on line number
> notes interspersed with the insn stream.
>
> In any case, if you build with -g and use in addition the "debug
> assembler output" flag -dA the assembler output should contain
> human-readable comments containing line number information.

The GCC assembler is never invoked.  After getting the assembler
output from the -S option, this is fed into IFOX00/IEV90/ASMA90.

Regardless, if line number notes are interspersed in the stream,
maybe whenever I write out an assembler instruction I will have
access to those notes and can print out a comment.

Thanks.  Paul.