On Tue, Nov 09, 2021 at 07:53:33PM +0100, Ard Biesheuvel wrote:
On Tue, 9 Nov 2021 at 19:49, Peter Zijlstra [off-list ref] wrote:
quoted
On Tue, Nov 09, 2021 at 05:45:44PM +0100, Ard Biesheuvel wrote:
quoted
diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h
index 5a00b8b2cf9f..0bb36294cce7 100644
--- a/include/linux/static_call_types.h
+++ b/include/linux/static_call_types.h
@@ -32,15 +32,20 @@
struct static_call_site {
s32 addr;
s32 key;
+ s32 tramp;
};
I can't say I'm thrilled at growing this thing, but the cleanup is nice.
Perhaps we can increase alignment on struct static_call_key and instead
frob it in .key still?
This is already a place-relative field, and one points into the data
section and the other into text. So I don't see how we can squeeze
enough bits out of it to make this fit.
Well, the actual address will be:
((unsigned long)&site->key + site->key)
either way around, right? Now, if we align struct static_call_key to 8,
that means the low 3 bits of that address will be 0 and free for us to
muck about with.
That is, we already use the low 2 bits of that (because natural
alignment etc.).
If we got 3 bits, we could shift the existing two bits one up and free
up bit0, then say that if bit0 is set, it's a trampoline address. The
only additional requirement would be that trampolines are (at least)
aligned 2 (they're at 4 currently).
Except.... it would be the linker having to create that field, and
there's no way that thing is smart like that :-( Ooh well.
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