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This commit removes all morestack support from the compiler which entails:
* Segmented stacks are no longer emitted in codegen.
* We no longer build or distribute libmorestack.a
* The `stack_exhausted` lang item is no longer required
The only current use of the segmented stack support in LLVM is to detect stack
overflow. This is no longer really required, however, because we already have
guard pages for all threads and registered signal handlers watching for a
segfault on those pages (to print out a stack overflow message). Additionally,
major platforms (aka Windows) already don't use morestack.
This means that Rust is by default less likely to catch stack overflows because
if a function takes up more than one page of stack space it won't hit the guard
page. This is what the purpose of morestack was (to catch this case), but it's
better served with stack probes which have more cross platform support and no
runtime support necessary. Until LLVM supports this for all platform it looks
like morestack isn't really buying us much.
cc #16012 (still need stack probes)
Closes #26458 (a drive-by fix to help diagnostics on stack overflow)
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Not included are two required patches:
* LLVM: segmented stack support for DragonFly [1]
* jemalloc: simple configure patches
[1]: http://reviews.llvm.org/D4705
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OS X 10.9's linker has a bug that results in it failing to preserve
DWARF unwind information when passed the -no_compact_unwind flag.
This flag is passed on OS X because the unwind information for
__morestack cannot be represented by the compact unwind format.
We can work around this problem by using a more targeted approach
to disabling compact unwind information. The OS X linker looks for
a particular pattern in the DWARF unwind information and will not
attempt to convert the unwind information to the compact format.
The pattern in question is the return address register being saved
twice to the same location.
Fixes #6849.
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This commit resumes management of the stack boundaries and limits when switching
between tasks. This additionally leverages the __morestack function to run code
on "stack overflow". The current behavior is to abort the process, but this is
probably not the best behavior in the long term (for deails, see the comment I
wrote up in the stack exhaustion routine).
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Win64 convention does not use underscore.
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Like I commented in #2043, I can't reproduce the weirdness from #1388 on either mac or linux (x84_64) and pushing to try gives all green.
That's 128 less bytes to have to keep in the stack for every call to __morestack.
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Closes #5643
This also removes the need to pass noexecstack to gcc, but that wasn't
actually working anymore.
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brson said the answer to the question is probably no... so I'm
going to be bold and remove this.
Closes #2685
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__morestack, close #1388.
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This doesn't matter now since we use an out pointer for return
values but it's sure to show up mysteriously someday.
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I haven't thought too deeply about this, but I think I was telling the
unwinder to use the stack pointer for the wrong frame when unwinding. Not sure
how that could have worked at all, but this results in the correct alignment
for cleanups.
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Had to bump the min stack size in some of the tests from 256 bytes
to 1024 bytes. Not sure why yet.
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The DW_CFA_val_offset_sf instruction doesn't seem to work on mac,
even after implementing it in the llvm-mc assembler, so now
I'm looking for a different way to communicate the stack pointer
adjustment to the unwinder.
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Had to bump the min stack size in some of the tests from 256 bytes
to 1024 bytes. Not sure why yet.
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The DW_CFA_val_offset_sf instruction doesn't seem to work on mac,
even after implementing it in the llvm-mc assembler, so now
I'm looking for a different way to communicate the stack pointer
adjustment to the unwinder.
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LLVM's assembler understands .cfi pseudo-ops on the mac, which we need in
order to generate frames that can be DWARF-unwound
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When unwinding through __morestack the stack limit in the TLS is invalidated
and must be reset. Instead of actually landing at __morestack we're
just going to make all our Rust landing pads call upcall_reset_stack_limit,
which will find the stack segment that corresponds to the current stack
pointer and put the limit in the TLS.
Also massively expand the stack segment red zone to make more room for the
dynamic linker. Will fix in the future.
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upcall_call_shim_on_c_stack does not handle return values
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Each crate will have its own copy of this function, which should not be
exported.
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