This ensures that gdb is able to generate a correct backtrace when
stopped at any instruction in the inline asm.
It also makes backtraces accessible to tools that only track frame
pointer chains, like perf or dtrace.
close#49
The use case is as follows: let's say I have a scheduler that uses
libfringe for context switching. A single thread may open several
sockets, each of which presents a std::io::Read interface, and
waiting in Read::read requires having a reference to the yielder
inside the socket.
This could be worked around with RefCell in the API consumer, but
there is no real reason to not implement it in libfringe.
close#48
This commit:
* Gets rid of 2nd init trampoline.
* Gets rid of any custom CFI, instead using the standard CFI
for target prologue.
* Makes backtraces accessible to tools that only track frame
pointer chains, like perf or dtrace.
* Keeps the performance at the exact same level.
This reverts a part of 365e40b. While it is not legal to clobber
the output register, it is legal and necessary to do this for inputs,
since we do not preserve them, and LLVM could have decided to
reuse them.
Thanks to @Amanieu for discovering this.
This is not actually legal (although the restriction is not
documented anywhere), and is not caught by LLVM unless the codegen
option -verify-machineinstrs is specified. This option is now used
on Travis.
While not legal, this does not seem to result in invalid output
(although it creates an unnecessary spill); however, under extremely
specific circumstances (e.g. when a register scavenger is run under
severe pressure), this will result in a codegen crash, which is
how I found it.
