linux-kernel - [PATCH] Partially revert "compiler: enable CONFIG_OPTIMIZE

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Date:   Mon, 30 Sep 2019 12:45:40 +0100
From:   Will Deacon <will@...nel.org>
To:     torvalds@...ux-foundation.org, yamada.masahiro@...ionext.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] Partially revert "compiler: enable CONFIG_OPTIMIZE_INLINING forcibly"

This reverts commit ac7c3e4ff401b304489a031938dbeaab585bfe0a for ARM and
arm64.

Building an arm64 kernel with CONFIG_OPTIMIZE_INLINING=y has been shown
to violate fixed register allocations of local variables passed to
inline assembly with GCC prior to version 9 which can lead to subtle
failures at runtime:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91111

A very similar has been reported for 32-bit ARM as well:

  https://lkml.kernel.org/r/f5c221f5749e5768c9f0d909175a14910d349456.camel@suse.de

Although GCC 9.1 appears to work for the specific case in the bugzilla
above, the exact issue has not been root-caused so play safe and disable
the option for now on these architectures.

Cc: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Russell King <linux@...linux.org.uk>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>,
Cc: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Will Deacon <will@...nel.org>
---
 lib/Kconfig.debug | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93d97f9b0157..c37c72adaeff 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -312,6 +312,7 @@ config HEADERS_CHECK
 
 config OPTIMIZE_INLINING
 	def_bool y
+	depends on !(ARM || ARM64) # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91111
 	help
 	  This option determines if the kernel forces gcc to inline the functions
 	  developers have marked 'inline'. Doing so takes away freedom from gcc to
-- 
2.23.0.444.g18eeb5a265-goog