linux-kernel - [PATCH] compiler: remove stringification from __ADDRESSABLE

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Message-ID: <561c52d6-9728-4dfc-a629-353dc2488c8b@suse.com>
Date: Wed, 12 Feb 2025 16:11:51 +0100
From: Jan Beulich <jbeulich@...e.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: Juergen Gross <jgross@...e.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: [PATCH] compiler: remove stringification from __ADDRESSABLE_ASM()

__ADDRESSABLE_ASM_STR() is where the necessary stringification happens.
As long as "sym" doesn't contain any odd characters, no quoting is
required for its use with .quad / .long. In fact the quotation gets in
the way with gas 2.25; it's only from 2.26 onwards that quoted symbols
are half-way properly supported.

Fixes: 0ef8047b737d ("x86/static-call: provide a way to do very early static-call updates")
Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: stable@...r.kernel.org
---
I think that __ADDRESSABLE_ASM{,_STR}() better would have a separate
comment, as that presently kind of shared with {_,}__ADDRESSABLE() isn't
really applicable to assembly code.

Is data allocation actually necessary in __ADDRESSABLE_ASM()? Aiui the
sole goal is to have sym in the symbol table. That could be achieved by
a simple .global (or e.g. .hidden) directive.

Shouldn't Xen's __ADDRESSABLE_xen_hypercall use STATIC_CALL_KEY() rather
than open-coding it?

--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -245,7 +245,7 @@ static inline void *offset_to_ptr(const
 #define __ADDRESSABLE_ASM(sym)						\
 	.pushsection .discard.addressable,"aw";				\
 	.align ARCH_SEL(8,4);						\
-	ARCH_SEL(.quad, .long) __stringify(sym);			\
+	ARCH_SEL(.quad, .long) sym;					\
 	.popsection;

 #define __ADDRESSABLE_ASM_STR(sym) __stringify(__ADDRESSABLE_ASM(sym))