[Mono-list] mcs targets/definitions

[Jonathan Pryor]

Attempted answers inline...

On Mon, 2003-09-08 at 23:42, Kenneth Brubaker wrote:
> (1) Would there be any reason to have a Release and Debug builds using the 
> current mcs? 

Not right now...

> I don't see any optimize flags. 

Exactly.  So what would a Release build add? :-)

Plus, with Debug builds it makes it easier for other developers.  (Yay
line number information in stack traces when run with "mono --debug"!)

> There is, of course a debug 
> flag (two for some reason--why?

Why?  Compatibility with Microsoft's CSC.EXE, which has "debugging
information" (/debug) and "lots of debugging information" (/debug+), if
memory serves.  I found it confusing at the time, myself...

Mcs is option-compatible with CSC.EXE (makes it easier to write
makefiles), so that's why MCS has the multiple debug options.

"-g" is a mcs extension, for all us GCC users who expect "-g" to be
present in all compilers, and curse Microsoft for not using -g as
well... ;-)

> ), but I always prefer to produce debug 
> symbols for my release builds. (Yes bugs CAN occur in release builds :-o )  
> Does the debug flag affect performance of the generated IL?

Any takers?

My partial answer is that there need not be a reason for debug
information to impact performance.  The primary reason C code has a
performance degradation with debug code is that x86 code loses a
register to store the "frame pointer," which is used to generate
accurate stack traces.  x86 is register starved as it is, so this
greatly contributes to the decline in code, assuming the code
optimizations are enabled.

.NET CIL permits much more accurate tracking of variables in code, so a
frame pointer isn't strictly needed, so it *should* be possible to get
create optimized code that also contains debug symbols and is useful for
debugging.

Whether mono actually does this, I can't say.

> (2) Is there a macro defintion built into the MCS compiler on the order of, 
> say, "MONO," so that conditional compilation can occur if, on the outside 
> chance, the implementation is not perfectly alligned with the MS FCL?

Yes... and No.  Yes, mcs defines __MonoCS__ symbol... and you should
ignore it. :-)

You should ignore it because it only says that your code is being
compiled with mcs.  It doesn't say that you're running under Mono on
Linux, Mono on Windows, or under .NET.  Which amounts to making it
worthless for signaling platform-dependent code.

The solution is to create your own symbol, and #if off that.  Or, use
runtime checks.  Or, make sure that Mono *is* perfectly aligned with
.NET's FCL by filing bugzilla bugs and contributing. :-)

> Kenneth Brubaker

 - Jon