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Re: Host/Target confusion in Dwarf output


Ian Lance Taylor wrote:
Michael Eager <eager@eagercon.com> writes:

It seems to me that the same assembly code should be generated
independent of whether gcc is run on a 32-bit or 64-bit
host and all of these HOST_* tests should actually be
target domain parameters, like BITS_PER_WORD.

It is sad but true that there are various cases in gcc which differ based on the size of an integer on the host. So far as I know none of them amount to bugs, but as you've seen they do lead to different code generation. The most obvious difference here is that CONST_INTs in RTL are stored as HOST_WIDE_INTs. And it is that difference which are you seeing, propagated into the debug code.

In this case, the difference is not trivial. On a 64-bit host, gcc generates code that the assembler rejects and, if I recall correctly, DWARF_FORM_8 which is not supported by the target binutils. That latter may be a binutils defect.

Either way, it counts as a bug if the compile doesn't finish.

Why would the RTL represent target CONST_INT as HOST_WIDE_INT?
Confusion between host and target?

I think that in general it would be good to fix these issues, so that
we generate the same assembler code for a given target from any host.
The cases to really think through in detail are a 32-bit host and a
64-bit target.

I don't have that combination, that could be problematic.


With the current definition of RTL, I don't think you can fix
dwarf2out.c independently of fixing other parts of the compiler.  But,
if I am wrong in that, go for it.

Jeez, I hope that's not the case. I don't want to start fixing a small problem in DWARF output and end up re-architecting the RTL. (I'm exaggerating, but only a little).


-- Michael Eager eager@eagercon.com 1960 Park Blvd., Palo Alto, CA 94306 650-325-8077


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