linux-kernel - [PATCH 39/46] x86, lto: Disable relative init pointers with gcc LTO

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Message-Id: <20221114114344.18650-40-jirislaby@kernel.org>
Date:   Mon, 14 Nov 2022 12:43:37 +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 39/46] x86, lto: Disable relative init pointers with gcc LTO

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

Relative init pointers are implemented using custom top-level assembler
that references the init function. With LTO, the top-level assembler
statement can end up in other assembler files than the init function,
which then causes linker errors if the init function was static.

This could be fixed by making all the init functions global, but that
would be a very intrusive change all over the tree.

Instead, disable relative init pointers for gcc LTO.

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/Kconfig | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 67745ceab0db..6455d843d559 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -176,7 +176,9 @@ config X86
 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
 	select HAVE_ARCH_COMPAT_MMAP_BASES	if MMU && COMPAT
-	select HAVE_ARCH_PREL32_RELOCATIONS
+	# LTO can move assembler to different files, so all
+	# the init functions would need to be global for this to work
+	select HAVE_ARCH_PREL32_RELOCATIONS	if !LTO_GCC
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_STACKLEAK
-- 
2.38.1