linux-kernel - [PATCH AUTOSEL 5.3 097/203] powerpc/Makefile: Always pass --synthetic to nm if supported

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Message-Id: <20190922184350.30563-97-sashal@kernel.org>
Date:   Sun, 22 Sep 2019 14:42:03 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Peter Collingbourne <pcc@...gle.com>,
        Will Deacon <will@...nel.org>, Sasha Levin <sashal@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.3 097/203] powerpc/Makefile: Always pass --synthetic to nm if supported

From: Michael Ellerman <mpe@...erman.id.au>

[ Upstream commit 117acf5c29dd89e4c86761c365b9724dba0d9763 ]

Back in 2004 we added logic to arch/ppc64/Makefile to pass
the --synthetic option to nm, if it was supported by nm.

Then in 2005 when arch/ppc64 and arch/ppc were merged, the logic to
add --synthetic was moved inside an #ifdef CONFIG_PPC64 block within
arch/powerpc/Makefile, and has remained there since.

That was fine, though crufty, until recently when a change to
init/Kconfig added a config time check that uses $(NM). On powerpc
that leads to an infinite loop because Kconfig uses $(NM) to calculate
some values, then the powerpc Makefile changes $(NM), which Kconfig
notices and restarts.

The original commit that added --synthetic simply said:
  On new toolchains we need to use nm --synthetic or we miss code
  symbols.

And the nm man page says that the --synthetic option causes nm to:
  Include synthetic symbols in the output. These are special symbols
  created by the linker for various purposes.

So it seems safe to always pass --synthetic if nm supports it, ie. on
32-bit and 64-bit, it just means 32-bit kernels might have more
symbols reported (and in practice I see no extra symbols). Making it
unconditional avoids the #ifdef CONFIG_PPC64, which in turn avoids the
infinite loop.

Debugged-by: Peter Collingbourne <pcc@...gle.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/Makefile | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index c345b79414a96..403f7e193833a 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -39,13 +39,11 @@ endif
 uname := $(shell uname -m)
 KBUILD_DEFCONFIG := $(if $(filter ppc%,$(uname)),$(uname),ppc64)_defconfig

-ifdef CONFIG_PPC64
 new_nm := $(shell if $(NM) --help 2>&1 | grep -- '--synthetic' > /dev/null; then echo y; else echo n; fi)

 ifeq ($(new_nm),y)
 NM		:= $(NM) --synthetic
 endif
-endif

 # BITS is used as extension for files which are available in a 32 bit
 # and a 64 bit version to simplify shared Makefiles.
-- 
2.20.1