linux-kernel - [PATCH 32/46] x86/realmode, lto: Disable gcc LTO for real mode code

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Message-Id: <20221114114344.18650-33-jirislaby@kernel.org>
Date:   Mon, 14 Nov 2022 12:43:30 +0100
From:   "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Martin Liska <mliska@...e.cz>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 32/46] x86/realmode, lto: Disable gcc LTO for real mode code

From: Andi Kleen <ak@...ux.intel.com>

The early real mode bootup code makes various assumptions that break
with LTO. For example it assumes that top level assembler statements
don't get reordered. Disable LTO for the real mode code.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Martin Liska <mliska@...e.cz>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/realmode/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/realmode/Makefile b/arch/x86/realmode/Makefile
index a0b491ae2de8..47b8b500cf15 100644
--- a/arch/x86/realmode/Makefile
+++ b/arch/x86/realmode/Makefile
@@ -10,6 +10,7 @@
 # Sanitizer runtimes are unavailable and cannot be linked here.
 KASAN_SANITIZE			:= n
 KCSAN_SANITIZE			:= n
+KBUILD_CFLAGS			+= $(DISABLE_LTO_GCC)
 
 subdir- := rm
 
-- 
2.38.1