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    SubjectStackleak vs noinstr (Was: [GIT pull] objtool/core for v5.16-rc1)
    On Tue, Nov 02, 2021 at 09:00:36AM +0100, Peter Zijlstra wrote:
    > On Mon, Nov 01, 2021 at 01:44:39PM -0700, Linus Torvalds wrote:

    > > do_machine_check()+0x27: call to stackleak_track_stack ...
    > > do_syscall_64()+0x9: call to stackleak_track_stack ...
    > > do_int80_syscall_32()+0x9: call to stackleak_track_stack ...
    > > exc_general_protection()+0x22: call to stackleak_track_stack ...
    > > fixup_bad_iret()+0x20: call to stackleak_track_stack ...
    > > .entry.text+0x10e6: call to stackleak_erase ...
    > > .entry.text+0x143: call to stackleak_erase ...
    > > .entry.text+0x17d9: call to stackleak_erase ...
    > >
    > > most seem to be about the stackleak thing,
    >
    > Right, I recently ran into this and hacen't yet had time to look into
    > it. I suspect my normal build box doesn't have the GCC plugin crud
    > enabled or somesuch.
    >
    > I think the GCC stackleak plugin needs fixing, specifically it needs a
    > function attribute such that it will not emit instrumentation in noinstr
    > functions. I'll go chase down the developer of that thing.

    Alexander, is there any way to make this plugin grow a function
    attribute which we can add to noinstr ? There's a strict requirement the
    compiler doesn't add extra code to noinstr functions these days.

    We'll 'soon' be running noinstr C code before switching to kernel page
    tables even.

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