linux-kernel - [PATCH] ARM: linker script: GCOV kernel may refers data in _

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Message-Id: <153580549235.10130.1495077983569784123.stgit@devbox>
Date:   Sat,  1 Sep 2018 21:38:13 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Nicolas Pitre <nicolas.pitre@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] ARM: linker script: GCOV kernel may refers data in __exit

GCOV kernel embeds counters in the kernel for each line
and a part of that embed in __exit text. So we need to
keep the __exit text if CONFIG_GCOV_KERNEL=y.

Without this patch, if we discards __exit text (e.g.
disables CONFIG_GENERIC_BUG, CONFIG_JUMP_LABEL and
CONFIG_SMP_ON_UP) but enables CONFIG_GCOV_PROFILE_FTRACE,
ld will error like below on ARM.

`.text.exit' referenced in section `.ARM.exidx.text.exit' of
kernel/trace/trace_clock.o: defined in discarded section `.text.exit'
of kernel/trace/trace_clock.o

To fix this issue, we keep __exit when CONFIG_GCOV_KERNEL=y.

The reason why not depending CONFIG_GCOV_PROFILE_X, is
that the Documentation/dev-tools/gcov.rst says that the
developer can enable gcov profile on a file or a directory
by customizing Makefile, and that will only depend on
CONFIG_GCOV_KERNEL.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Reported-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm/kernel/vmlinux.lds.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/vmlinux.lds.h b/arch/arm/kernel/vmlinux.lds.h
index ae5fdff18406..baaacee9f5ce 100644
--- a/arch/arm/kernel/vmlinux.lds.h
+++ b/arch/arm/kernel/vmlinux.lds.h
@@ -9,7 +9,8 @@
 #endif

 #if (defined(CONFIG_SMP_ON_UP) && !defined(CONFIG_DEBUG_SPINLOCK)) || \
-	defined(CONFIG_GENERIC_BUG) || defined(CONFIG_JUMP_LABEL)
+	defined(CONFIG_GENERIC_BUG) || defined(CONFIG_JUMP_LABEL) || \
+	defined(CONFIG_GCOV_KERNEL)
 #define ARM_EXIT_KEEP(x)	x
 #define ARM_EXIT_DISCARD(x)
 #else