linux-kernel - [PATCH v2] compiler: remove __ADDRESSABLE_ASM{

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Message-ID: <945716d2-4dd4-4d38-b732-41ab8b27c5ee@suse.com>
Date: Mon, 17 Feb 2025 17:40:09 +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>,
 Stefano Stabellini <sstabellini@...nel.org>
Subject: [PATCH v2] compiler: remove __ADDRESSABLE_ASM{_STR,}() again

__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.

However, assembly being different from C anyway, drop
__ADDRESSABLE_ASM_STR() and its helper macro altogether. A simple
.global directive will suffice to get the symbol "declared", i.e. into
the symbol table. While there also stop open-coding STATIC_CALL_TRAMP()
and STATIC_CALL_KEY().

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
---
v2: Drop constructs instead of fixing them. Use STATIC_CALL_KEY().
---
Whether the "ADDRESSABLE" in __ADDRESSABLE_xen_hypercall is still
meaningful to keep I'm uncertain about. The situation, as said, is quite
different in assembly, compared to C's requirements.

--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -242,14 +242,6 @@ static inline void *offset_to_ptr(const
 #define __ADDRESSABLE(sym) \
 	___ADDRESSABLE(sym, __section(".discard.addressable"))
 
-#define __ADDRESSABLE_ASM(sym)						\
-	.pushsection .discard.addressable,"aw";				\
-	.align ARCH_SEL(8,4);						\
-	ARCH_SEL(.quad, .long) __stringify(sym);			\
-	.popsection;
-
-#define __ADDRESSABLE_ASM_STR(sym) __stringify(__ADDRESSABLE_ASM(sym))
-
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -94,12 +94,13 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_h
 #ifdef MODULE
 #define __ADDRESSABLE_xen_hypercall
 #else
-#define __ADDRESSABLE_xen_hypercall __ADDRESSABLE_ASM_STR(__SCK__xen_hypercall)
+#define __ADDRESSABLE_xen_hypercall \
+	__stringify(.global STATIC_CALL_KEY(xen_hypercall);)
 #endif
 
 #define __HYPERCALL					\
 	__ADDRESSABLE_xen_hypercall			\
-	"call __SCT__xen_hypercall"
+	__stringify(call STATIC_CALL_TRAMP(xen_hypercall))
 
 #define __HYPERCALL_ENTRY(x)	"a" (x)