linux-kernel - [PATCH v2 3/4] kbuild: Remove MFS flags from Propeller profile generate builds

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Message-ID: <20251014191156.3836703-4-xur@google.com>
Date: Tue, 14 Oct 2025 19:11:55 +0000
From: xur@...gle.com
To: Alexey Gladkov <legion@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Ard Biesheuvel <ardb@...nel.org>, Bill Wendling <morbo@...gle.com>, Han Shen <shenhan@...gle.com>, 
	Ingo Molnar <mingo@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Masahiro Yamada <masahiroy@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Nicolas Schier <nicolas.schier@...ux.dev>, 
	Peter Zijlstra <peterz@...radead.org>, Tamir Duberstein <tamird@...il.com>, 
	Thomas Gleixner <tglx@...utronix.de>, 
	"Thomas Weißschuh" <thomas.weissschuh@...utronix.de>, Yabin Cui <yabinc@...gle.com>, 
	Sriraman Tallam <tmsriram@...gle.com>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, Rong Xu <xur@...gle.com>
Subject: [PATCH v2 3/4] kbuild: Remove MFS flags from Propeller profile
 generate builds

From: Rong Xu <xur@...gle.com>

Propeller profile generation requires Machine Function Splitter (MFS)
to be disabled.

Change-Id: I12579e6f2cfaecefbed0ce85f1904f79783562a1
Signed-off-by: Rong Xu <xur@...gle.com>
---
 scripts/Makefile.propeller | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/Makefile.propeller b/scripts/Makefile.propeller
index fa018098506b8..8c3e514dbcc04 100644
--- a/scripts/Makefile.propeller
+++ b/scripts/Makefile.propeller
@@ -13,8 +13,14 @@ else
   else
     CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels
   endif
+  # Disable Machine Function Splitter for Propeller.
+  # Propeller profile generation requires Machine Function Splitter to be disabled.
+  # We use -fno-split-machine-functions to override any prior AutoFDO/PGO flags
+  #(in Makefile.lib), assuming Propeller options are applied afterward.
+  CFLAGS_PROPELLER_CLANG += -fno-split-machine-functions
 endif
 
+
 # Propeller requires debug information to embed module names in the profiles.
 # If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO,
 # as the option should already be set.
@@ -33,6 +39,8 @@ ifdef CONFIG_LTO_CLANG_THIN
     else
        _ldflags_propeller += --lto-basic-block-sections=labels
     endif
+    # Again, we need to disable Machine Function Splitter.
+    LDFLAGS_vmlinux := $(filter-out -plugin-opt=-split-machine-functions, $(LDFLAGS_vmlinux))
   endif
 endif
 
-- 
2.51.0.788.g6d19910ace-goog