Re: [Qemu-devel] Thoughts around dtrace linking...

[Lee Essen]

On 21/03/2012 13:01, Andreas Färber wrote:
> Hi,
>
> Am 21.03.2012 11:45, schrieb Lee Essen:
> > I've been trying to find a sensible way to solve the Solaris/Illumos
> > dtrace requirement to pass all the objs to the dtrace command so that
> > the resultant object file contains all the symbols needed to properly
> > link the relevant binary.
>
> The two issues I see (as info for Stefan et al.) are
> a) compiling DTrace probes into .o files requires linking those objects
> with that additional .o file to avoid linker errors (even for tools
> where using DTrace probes does not seem to make much sense),
> b) the additional .o file depends on its input .o files, so must be
> unique per executable.
> This seems to be guaranteed when doing it at rules.mak level. Haven't
> checked all the variables being passed back and forth here yet though; I
> really am not comfortable reviewing code that's HTML-formatted in my
> mailer. ;)

Sorry ... I've been jumping between machines and I'd thought I'd 
switched them all to plaintext, but obviously not. Hopefully this is 
done now.

New version below ...

> > How compatible is this with FreeBSD - it doesn't sound like it's needed
> > at all?
>
> Don't know about FreeBSD but on Darwin that step is indeed not needed or
> supported, so needs to be guarded.
>
> Andreas

Ok, so perhaps the easiest way to guard would be a new variable that 
matches both a backend of dtrace and OS of Solaris established via 
configure, for the moment I've just put a backend check, but clearly 
this wouldn't be enough.

LINK = $(call quiet-command,$(CC) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o 
$@ $(sort $(1)) $(LIBS),"  LINK  $(TARGET_DIR)$@")

DTRACE = $(call quiet-command,dtrace $(CONFIG_DTRACE_FLAGS) -o 
$(1)-dtrace.o -G -s $(2) $(3), "  GEN $(TARGET_DIR)$(1)-dtrace.o")

%$(EXESUF): %.o
ifeq ($(TRACE_BACKEND),dtrace)
  $(call DTRACE,$*,trace-dtrace.dtrace,$^)
  $(call LINK,$^ $*-dtrace.o)
else
  $(call LINK,$^)
endif

If you're happy that this is a sensible approach I'll put together a 
proper patch.

Regards,

Lee.