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    SubjectRe: strace-4.18 test suite oopses sparc64 4.12 and 4.13-rc kernels
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    From: Sam Ravnborg <sam@ravnborg.org>
    Date: Wed, 2 Aug 2017 23:36:47 +0200

    > And memset calls down to bzero, where %o0=buf, %o1=len
    >
    > %o0 = 0xc
    > %o1 = 0xfff000123c897a80
    > %o2 = 0x0
    > %o3 = 0xc
    >
    > So from this we know that:
    > res = 0xfff000123c897a80
    > to + (n - 0xfff000123c897a80)) = 0xc
    >
    > The value "fff000123c897a80" really looks like a constructed address
    > from somewhere in the strace code, and where this constructed address
    > is used to provoke some unusual behaviour.
    > The "fff0" part may be a sparc thing.
    >
    > So far the analysis seems to match the intial conclusion that
    > we in this special case try to zero out the remaining memory
    > based on the return value of raw_copy_from_user.
    > And therefore we use the return value (res) which triggers the oops.

    Yes, the return value is bogus.

    > So rather than manipulating with the assembler code as suggested
    > in the previous mail this simpler patch could be tested:
    ...
    > - memset(to + (n - res), 0, res);
    > + void: /*memset(to + (n - res), 0, res);*/

    Need a semicolon rather than a colon there :-)

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