OpenAFS Master Repository branch, master, updated. BP-openafs-stable-1_8_x-435-g0a39efe

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit 0a39efee224e8d4431ae79281ca353a7ba6fdce4
Author: Andrew Deason <adeason@dson.org>
Date:   Sun Jul 14 17:31:30 2019 -0500

    FBSD: Use ucontext for FreeBSD 10+ on amd64
    
    Currently, running any LWP program on recent FreeBSD on amd64 causes
    (or can cause) a SIGBUS very quickly. This is possibly because our
    stack management code in LWP only ensures our stacks are 4 or 8-byte
    aligned in most cases (except DARWIN, which gets 16-byte-aligned
    stacks), according to the value of STACK_ALIGN. The amd64 ABI mandates
    that stacks be 16-byte-aligned, and some function calls assume that
    this is followed, causing a SIGBUS when it is not. FreeBSD on amd64
    currently uses process.amd64.s for its savecontext() implementation,
    which does not do any checking or fixup of the stack alignment.
    
    This behavior has been observed on amd64 with FreeBSD 11 specifically,
    but it probably happens on any FreeBSD release when using clang.
    FreeBSD switched to clang as the default compiler with FreeBSD 10, so
    this probably occurs with FreeBSD 10 and newer.
    
    We could perhaps try to fix this by changing our stack management
    code, but we can also avoid most of this nonsense by just using
    ucontext instead of our custom assembly code. So, do that, by setting
    USE_UCONTEXT for FreeBSD 10+. Also enable the same 'stackvar'-based
    workaround in savecontext() as Linux uses, since otherwise 'topstack'
    appears to always be NULL, and triggers our stack overflow checks.
    
    Note that while LWP use is deprecated, as of this commit many small
    utilities (like 'fs') are still linked to LWP, and so are unusable
    without a fix like this.
    
    Change-Id: Ie8e928bd71e7f6e9c0fb1379259c55527b6ccdf3
    Reviewed-on: https://gerrit.openafs.org/13691
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
    Tested-by: Benjamin Kaduk <kaduk@mit.edu>

 src/config/param.amd64_fbsd_100.h |    2 ++
 src/config/param.amd64_fbsd_101.h |    2 ++
 src/config/param.amd64_fbsd_102.h |    2 ++
 src/config/param.amd64_fbsd_103.h |    2 ++
 src/config/param.amd64_fbsd_104.h |    2 ++
 src/config/param.amd64_fbsd_110.h |    2 ++
 src/config/param.amd64_fbsd_111.h |    2 ++
 src/config/param.amd64_fbsd_112.h |    2 ++
 src/config/param.amd64_fbsd_120.h |    2 ++
 src/lwp/Makefile.in               |    2 ++
 src/lwp/process.c                 |   14 +++++++++-----
 11 files changed, 29 insertions(+), 5 deletions(-)

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