Remove libsupport

[farcaller]

Thank's to hacker news post I'm now aware of rlibc crate. This should replace a big chunk of code in support.

• add dependency on rlibc crate
• move other parts of support into libzinc and verify that it still works
• verify that binary size didn't increase for whatever reason

[errordeveloper]

👍

[errordeveloper]

@farcaller we can tick the first box with errordeveloper/zinc@df6567d ;)

[farcaller]

Does it still work with duplicate symbols being defined in rlibc and libsupport? Anyways, we need to remove them from libsupport, can you make a PR please?

[errordeveloper]

@farcaller #113. I think I might have just got a very obscure error due to the duplicated symbols... let me figure it out...

[errordeveloper]

I think I might have just got a very obscure error due to the duplicated symbols... let me figure it out...

That was nothing to do with that. It was me calling rlibc from support.rs that somehow got the compiler confused and it produced a rather cryptic message:

Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/llvm/include/llvm/Support/Casting.h, line 237.

Just thought I'd document it...

[errordeveloper]

@farcaller could you elaborate a little bit on what you mean in the 2nd todo item, which says "move other parts of support into libzinc and verify that it still works"...

[farcaller]

The remaining bits of libsupport make little sense outside of libzinc. It makes sense to just move them somewhere into libzinc and drop the additional crate.

[errordeveloper]

I see, so I just tried trimming down what's left, and looks like without the following functions it compiles okay:

• unwind_phase2_forced()
• unwind_phase2()
• rust_fail_bounds_check()
• rust_begin_unwind()

Do you think the above are really not needed any more and all we need are the ones below?

• breakpoint()
• abort()
• __aeabi_unwind_cpp_pr0()
• __aeabi_unwind_cpp_pr1()
• get_eit_entry()

[farcaller]

It's quite surprising that abort() is not needed anymore. Can you try using unsafe { core::intrinsics::abort() } somewhere and see what assembly it materialises in?

[errordeveloper]

@farcaller I mean other way round, the list that includes abort() is certainly needed, while removing the rust_*() and unwind_*() doesn't break the build.

[farcaller]

Ah. fine :-) yup, that's fine, just make sure they're not getting included from compiler runtime :-)

[errordeveloper]

I only seem to grep out one of those:

> git grep -n -p rust_begin_unwind
RELEASES.txt=299=Version 0.9 (January 2014)
RELEASES.txt:401:      * std: The `rust_begin_unwind` function, useful for inserting breakpoints
src/libcore/lib.rs:41://! * `rust_begin_unwind` - This function takes three arguments, a
src/librustc/middle/weak_lang_items.rs=120=weak_lang_items!(
src/librustc/middle/weak_lang_items.rs:121:    begin_unwind,       BeginUnwindLangItem,        rust_begin_unwind;
src/librustrt/unwind.rs=340=pub mod eabi {
src/librustrt/unwind.rs:385:pub extern fn rust_begin_unwind(msg: &fmt::Arguments,

The rest do not appear to be around, could they had been renamed?