Re: [GIT PULL] x86/urgent for v5.11-rc7

On Mon, Feb 08, 2021 at 09:33:00AM -0600, Josh Poimboeuf wrote:

On Mon, Feb 08, 2021 at 10:02:06AM -0500, Steven Rostedt wrote:

quoted

On Sun, 7 Feb 2021 16:45:40 -0600
Josh Poimboeuf [off-list ref] wrote:

quoted

quoted

I do suspect involved people should start thinking about how they want
to deal with functions starting with

        endbr64
        call __fentry__

instead of the call being at the very top of the function.  

FWIW, objtool's already fine with it (otherwise we would have discovered
the need to disable fcf-protection much sooner).

And this doesn't really affect tracing (note, another user that might be
affected is live kernel patching).

Good point, livepatch is indeed affected.  Is there a better way to get
the "call __fentry__" address for a given function?


/*
 * Convert a function address into the appropriate ftrace location.
 *
 * Usually this is just the address of the function, but on some architectures
 * it's more complicated so allow them to provide a custom behaviour.
 */
#ifndef klp_get_ftrace_location
static unsigned long klp_get_ftrace_location(unsigned long faddr)
{
	return faddr;
}
#endif

I suppose the trivial fix is to see if it points to endbr64 and if so,
increment the addr by the length of that.