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Use a range to identify SIGSEGV in stack guards #47912

Merged
merged 2 commits into from
Feb 5, 2018
Merged

Use a range to identify SIGSEGV in stack guards #47912

merged 2 commits into from
Feb 5, 2018

Commits on Jan 31, 2018

  1. Enable stack-probe tests with system LLVM >= 5.0

    @cuviper
    cuviper committed Jan 31, 2018
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  2. Use a range to identify SIGSEGV in stack guards 

    Previously, the `guard::init()` and `guard::current()` functions were
returning a `usize` address representing the top of the stack guard,
respectively for the main thread and for spawned threads.  The `SIGSEGV`
handler on `unix` targets checked if a fault was within one page below
that address, if so reporting it as a stack overflow.

Now `unix` targets report a `Range<usize>` representing the guard
memory, so it can cover arbitrary guard sizes.  Non-`unix` targets which
always return `None` for guards now do so with `Option<!>`, so they
don't pay any overhead.

For `linux-gnu` in particular, the previous guard upper-bound was
`stackaddr + guardsize`, as the protected memory was *inside* the stack.
This was a glibc bug, and starting from 2.27 they are moving the guard
*past* the end of the stack.  However, there's no simple way for us to
know where the guard page actually lies, so now we declare it as the
whole range of `stackaddr ± guardsize`, and any fault therein will be
called a stack overflow.  This fixes rust-lang#47863.
    @cuviper
    cuviper committed Jan 31, 2018
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