The patch titled
Subject: Compiler attributes: introduce the LLVM __preserve_most function attribute
has been added to the -mm mm-nonmm-unstable branch. Its filename is
compiler-attributes-introduce-the-__preserve_most-function-attribute.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/compiler-attributes-introduce-the-__preserve_most-function-attribute.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: Compiler attributes: introduce the LLVM __preserve_most function attribute
Date: Wed, 2 Aug 2023 17:06:37 +0200
[1]: "On X86-64 and AArch64 targets, this attribute changes the calling
convention of a function. The preserve_most calling convention attempts
to make the code in the caller as unintrusive as possible. This
convention behaves identically to the C calling convention on how
arguments and return values are passed, but it uses a different set of
caller/callee-saved registers. This alleviates the burden of saving and
recovering a large register set before and after the call in the
caller."
[1] https://clang.llvm.org/docs/AttributeReference.html#preserve-most
Use of this attribute results in better code generation for calls to
very rarely called functions, such as error-reporting functions, or
rarely executed slow paths.
Introduce the attribute to compiler_attributes.h.
Link: https://lkml.kernel.org/r/20230802150712.3583252-1-elver@xxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Tom Rix <trix@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/compiler_attributes.h | 11 +++++++++++
1 file changed, 11 insertions(+)
--- a/include/linux/compiler_attributes.h~compiler-attributes-introduce-the-__preserve_most-function-attribute
+++ a/include/linux/compiler_attributes.h
@@ -322,6 +322,17 @@
#endif
/*
+ * Optional: not supported by gcc.
+ *
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#preserve-most
+ */
+#if __has_attribute(__preserve_most__)
+# define __preserve_most __attribute__((__preserve_most__))
+#else
+# define __preserve_most
+#endif
+
+/*
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
*/
#define __pure __attribute__((__pure__))
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
compiler-attributes-introduce-the-__preserve_most-function-attribute.patch
list_debug-introduce-inline-wrappers-for-debug-checks.patch
list_debug-introduce-config_debug_list_minimal.patch
