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Message-Id: <20250429-noautoinline-v3-8-4c49f28ea5b5@uniontech.com>
Date: Tue, 29 Apr 2025 12:06:12 +0800
From: Chen Linxuan via B4 Relay <devnull+chenlinxuan.uniontech.com@...nel.org>
To: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
Andrew Morton <akpm@...ux-foundation.org>,
Yishai Hadas <yishaih@...dia.com>, Jason Gunthorpe <jgg@...pe.ca>,
Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
Kevin Tian <kevin.tian@...el.com>,
Alex Williamson <alex.williamson@...hat.com>,
Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nicolas Schier <nicolas.schier@...ux.dev>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Brendan Jackman <jackmanb@...gle.com>,
Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>,
Juergen Gross <jgross@...e.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, kvm@...r.kernel.org, virtualization@...ts.linux.dev,
linux-integrity@...r.kernel.org, linux-kbuild@...r.kernel.org,
llvm@...ts.linux.dev, Winston Wen <wentao@...ontech.com>,
kasan-dev@...glegroups.com, xen-devel@...ts.xenproject.org,
Chen Linxuan <chenlinxuan@...ontech.com>,
Changbin Du <changbin.du@...el.com>
Subject: [PATCH RFC v3 8/8] lib/Kconfig.debug: introduce
CONFIG_NO_AUTO_INLINE
From: Chen Linxuan <chenlinxuan@...ontech.com>
Add a new kernel hacking option CONFIG_NO_AUTO_INLINE that prevents the
compiler from auto-inlining functions not explicitly marked with the
'inline' keyword.
This enhancement improves function tracer capabilities as it can only
trace functions that haven't been inlined by the compiler.
Previous discussions:
Link: https://lore.kernel.org/all/20181028130945.23581-3-changbin.du@gmail.com/
This patch is modified from commit 917fad29febd ("kernel hacking: add a
config option to disable compiler auto-inlining") which can be founded
in linux-next-history:
Link: https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next-history.git/commit/?id=917fad29febd
Cc: Changbin Du <changbin.du@...il.com>
Co-developed-by: Winston Wen <wentao@...ontech.com>
Signed-off-by: Winston Wen <wentao@...ontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@...ontech.com>
---
Makefile | 16 ++++++++++++++++
lib/Kconfig.debug | 21 +++++++++++++++++++++
lib/Makefile | 3 +++
3 files changed, 40 insertions(+)
diff --git a/Makefile b/Makefile
index 5aa9ee52a765b7aed27f44028cdcc34a90979acb..60dec6c123543150a3332a9a819fa6933e94db4f 100644
--- a/Makefile
+++ b/Makefile
@@ -1073,6 +1073,22 @@ endif
# Ensure compilers do not transform certain loops into calls to wcslen()
KBUILD_CFLAGS += -fno-builtin-wcslen
+ifdef CONFIG_NO_AUTO_INLINE
+# -fno-inline-functions behaves differently between gcc and clang.
+# With gcc, it prevents auto-inlining of functions but still considers functions
+# explicitly marked with "inline" for inlining. However, with clang, the flag
+# prevents inlining of all functions, including those explicitly marked with
+# inline. Clang provides the "-finline-hint-functions" option, which
+# specifically allows inlining of functions marked with "inline".
+#
+# In summary, to achieve equivalent behavior across compilers:
+# -fno-inline-functions (gcc) = -fno-inline-functions + -finline-hint-functions (clang)
+KBUILD_CFLAGS += -fno-inline-functions \
+ $(call cc-option, -finline-hint-functions) \
+ $(call cc-option, -fno-inline-small-functions) \
+ $(call cc-option, -fno-inline-functions-called-once)
+endif
+
# change __FILE__ to the relative path to the source directory
ifdef building_out_of_srctree
KBUILD_CPPFLAGS += $(call cc-option,-ffile-prefix-map=$(srcroot)/=)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f9051ab610d54358b21d61c141b737bb345b4cee..56530f0145c885e9846dae1d2f8c6125c610d25b 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -436,8 +436,29 @@ config GDB_SCRIPTS
instance. See Documentation/process/debugging/gdb-kernel-debugging.rst
for further details.
+
endif # DEBUG_INFO
+config NO_AUTO_INLINE
+ bool "Disable compiler auto-inline optimizations (EXPERIMENTAL)"
+ default n
+ help
+ This will prevent the compiler from optimizing the kernel by
+ auto-inlining functions not marked with the inline keyword.
+ With this option, only functions explicitly marked with
+ "inline" will be inlined. This will allow the function tracer
+ to trace more functions because it only traces functions that
+ the compiler has not inlined.
+
+ Note that Clang with -O2 optimization does not fully support
+ disabling all inline-related optimizations,
+ as Clang does not support options like
+ -fno-inline-small-functions and -fno-inline-functions-called-once
+ that gcc does.
+ Some functions without the inline keyword may still be inlined.
+
+ If unsure, select N.
+
config FRAME_WARN
int "Warn for stack frames larger than"
range 0 8192
diff --git a/lib/Makefile b/lib/Makefile
index f07b24ce1b3f8db28796e461db1324d97133fdd5..2ac97f0856a12f66e6c3825af6aabafa61869262 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -87,6 +87,9 @@ obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
# FIXME: Clang breaks test_bitmap_const_eval when KASAN and GCOV are enabled
GCOV_PROFILE_test_bitmap.o := n
+# FIXME:
+# Clang breaks test_bitmap_const_eval when NO_AUTO_INLINE and KASAN are enabled
+CFLAGS_test_bitmap.o += -finline-functions
endif
obj-$(CONFIG_TEST_UUID) += test_uuid.o
--
2.43.0
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