[PATCH v2] compiler: remove __ADDRESSABLE_ASM{_STR,}() again

From: Jan Beulich
Date: Mon Feb 17 2025 - 11:41:03 EST


__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@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
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)