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    SubjectRe: [PATCH] compiler: enable CONFIG_OPTIMIZE_INLINING forcibly
    On Fri, Sep 27, 2019 at 03:38:44PM -0700, Linus Torvalds wrote:
    > On Fri, Sep 27, 2019 at 3:08 PM Nick Desaulniers
    > <ndesaulniers@google.com> wrote:
    > >
    > > So get_user() was passed a bad value/pointer from userspace? Do you
    > > know which of the tree calls to get_user() from sock_setsockopt() is
    > > failing? (It's not immediately clear to me how this patch is at
    > > fault, vs there just being a bug in the source somewhere).
    >
    > Based on the error messages, the SO_PASSCRED ones are almost certainly
    > from the get_user() in net/core/sock.c: sock_setsockopt(), which just
    > does
    >
    > if (optlen < sizeof(int))
    > return -EINVAL;
    >
    > if (get_user(val, (int __user *)optval))
    > return -EFAULT;
    >
    > valbool = val ? 1 : 0;
    >
    > but it's the other messages imply that a lot of other cases are
    > failing too (ie the "Failed to bind netlink socket" is, according to
    > google, a bind() that fails with the same EFAULT error).
    >
    > There are probably even more failures that happen elsewhere and just
    > don't even syslog the fact. I'd guess that all get_user() calls just
    > fail, and those are the ones that happen to get printed out.
    >
    > Now, _why_ it would fail, I have ni idea. There are several inlines in
    > the arm uaccess.h file, and it depends on other headers like
    > <asm/domain.h> with more inlines still - eg get/set_domain() etc.
    >
    > Soem of that code is pretty subtle. They have fixed register usage
    > (but the asm macros actually check them). And the inline asms clobber
    > the link register, but they do seem to clearly _state_ that they
    > clobber it, so who knows.
    >
    > Just based on the EFAULT, I'd _guess_ that it's some interaction with
    > the domain access control register (so that get/set_domain() thing).
    > But I'm not even sure that code is enabled for the Rpi2, so who
    > knows..

    FWIW, we've run into issues with CONFIG_OPTIMIZE_INLINING and local
    variables marked as 'register' where GCC would do crazy things and end
    up corrupting data, so I suspect the use of fixed registers in the arm
    uaccess functions is hitting something similar:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91111

    Although this particular case couldn't be reproduced with GCC 9, prior
    versions of the compiler get it wrong so I'm very much opposed to enabling
    CONFIG_OPTIMIZE_INLINING by default on arm/arm64.

    Will

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