[haiku-development] Re: A modest (FatELF) proposal
- From: David Given <dg@xxxxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Tue, 20 Nov 2012 20:12:08 +0000
On 20/11/12 08:14, Ingo Weinhold wrote:
[...]
> Probably not. But do I understand you correctly that one could at least
> get away with one generic 32 bit version and one generic 64 bit version?
> Maybe even roll those two into one fat version -- the diff between them
> might not be that big.
Yes and no. That does solve the memory layout problem. But it doesn't
deal with code like this:
#if defined __x86__
printf("Ew.\n");
#elif defined __ARM__
printf("Hurrah!\n")
#endif
We solved this by defining our own custom platform, AGP, and isolating
the program from any platform-specific features at the bytecode level.
So structures and stack frames aren't laid out the x86 SysV way or the
ARMv7 EABI way or the MIPS way, they're laid out the AGP way. We support
limited ABI compatibility with the host platform which extends as far as
non-varargs C function calls, but no more.
C++ is supported, but only within an AGP binary --- the interfaces to
the outside world are C only; the C++ calling conventions are just too
hideously evil. Consider the gcc2 vs gcc4 ABI problems that Haiku's got
right now! We didn't even consider allowing interoperability with the
host, where we can't even tell in advance what compiler it's using.
So in order for this to work it's probably necessary to define a special
Haiku Portable Executable platform for which programs are compiled, and
then define a minimal syscall interface between HPE programs and the
rest of the world. It *may* be possible to use some of LLVM's very cool
dynamic code generation facilities to automatically build bindings
between HPE code and the host C++ interfaces, but that's way beyond my
expertise.
In a way it's a shame that Haiku relies so heavily on C++; it does
hugely complicate any ABI issues. C interfaces are so much simpler.
--
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â sufficient to punt the elastic spherical cow into low orbit." ---
â Brooks Moses on r.a.sf.c
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