linux-kernel - [PATCH] kbuild, x86: drop unnecessary prefix map configuration

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Message-Id: <20250322-asm-prefix-map-v1-1-ffe92c80b4d4@weissschuh.net>
Date: Sat, 22 Mar 2025 10:03:16 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Masahiro Yamada <masahiroy@...nel.org>, 
 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>, 
 Nicolas Schier <nicolas@...sle.eu>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Nathan Chancellor <nathan@...nel.org>, Ben Hutchings <ben@...adent.org.uk>, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] kbuild, x86: drop unnecessary prefix map configuration

The toplevel Makefile already provides -ffile-prefix-map as part of
KBUILD_CPPFLAGS. In contrast to the KBUILD_CFLAGS and KBUILD_AFLAGS
variables, KBUILD_CPPFLAGS is not redefined in the architecture specific
Makefiles. Therefore the toplevel KBUILD_CPPFLAGS do apply just fine, to
both C and ASM sources.

The custom configuration was necessary when it was added in
commit 9e2276fa6eb3 ("arch/x86/boot: Use prefix map to avoid embedded paths")
but has since become unnecessary in
commit a716bd743210 ("kbuild: use -fmacro-prefix-map for .S sources")

Drop the now unnecessary custom prefix map configuration.

Link: https://lore.kernel.org/lkml/d250e864d6d81cc02e2599f710872f72d58a3c29.camel@decadent.org.uk/
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
Intended to go through the kbuild tree.

It would have been nice to have this before
"kbuild: make all file references relative to source root",
but I guess it's really not worth a rebase and the complexity.
---
 arch/x86/boot/Makefile            | 1 -
 arch/x86/boot/compressed/Makefile | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index f500f82864aae80deb74faa3df9a8b6333d6c4ca..75e7a76deee1541ffed05953eb0574f14fe193a9 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -54,7 +54,6 @@ targets += cpustr.h

 KBUILD_CFLAGS	:= $(REALMODE_CFLAGS) -D_SETUP
 KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
-KBUILD_CFLAGS	+= $(call cc-option,-ffile-prefix-map=$(srctree)/=)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS	+= $(CONFIG_CC_IMPLICIT_FALLTHROUGH)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index ad324978b2e5b1b6f8be82647769c99db8257ac7..4d3f714ad8717db2235a707269d26565a9671187 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -38,7 +38,6 @@ KBUILD_CFLAGS += -fno-stack-protector
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
 KBUILD_CFLAGS += -Wno-pointer-sign
-KBUILD_CFLAGS += $(call cc-option,-ffile-prefix-map=$(srctree)/=)
 KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS += -D__DISABLE_EXPORTS
 # Disable relocation relaxation in case the link is not PIE.

---
base-commit: 1a78774bb35068bb143d2299da3f8a0b87807cdb
change-id: 20250322-asm-prefix-map-028f044d87b3

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>