[Bug libc/759] [i386] getcontext() not setting arg's uc_stack correctly

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https://sourceware.org/bugzilla/show_bug.cgi?id=759

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9995c839a01cd8db17120cb2c0a80f81d858b179

commit 9995c839a01cd8db17120cb2c0a80f81d858b179
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue May 16 16:05:35 2017 -0300

    manual: Document getcontext uc_stack value on Linux [BZ #759]

    As decribed in BZ#759, Linux getcontext implementation on Linux does
    differs from other SysV system about the returned uc_stack.  This is
    true not only for i386, but for all the architecture I could actually
    check (aarch64, arm, alpha, hppa, m68k, mips, mips64, mips64n32,
    powerpc, powerpc64, powerpc64le, s390x, sh, sparc, sparc64, and x86).

    And I think we should not change current behavior for some reasons:

    1. POSIX 2008 removed this SySV interface for a good reason and changing
       this behavior adds nothing for current portable code.  POSIX 2001
       specification does states that stack should be saved [1] and current
       GLIBC code does in a arch-specific manner (inside the mcontext_t)
       which allows the setcontext to work correctly.

    2. Changing this behavior would potentially require compat symbols and
       I see no gain in adding compat symbols for deprecated interfaces.

    3. Also, for comment #2 in BZ#759, it is up to kernel do setup the contents
       for ucontext_t and currently it does not provide the stack information
       as well.  Trying to change it is also another fix that does not worth
       the possible gains.

    Instead my proposal is to make it clear the current interface may differ
    depending of the underlying operational system.

    glibc documentation and close this bug as invalid.

        [BZ #759]
        * manual/setjmp.texi (getcontex): Document uc_stack value on Linux.

    [1]
http://pubs.opengroup.org/onlinepubs/009695399/functions/getcontext.html

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Summary of changes:
 ChangeLog          |    6 ++++++
 manual/setjmp.texi |    5 +++++
 2 files changed, 11 insertions(+), 0 deletions(-)

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