linux-kernel - [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

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Date:   Mon, 10 Oct 2016 14:56:56 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

I have no idea what is actually going on here, but building an x86 kernel
with CONFIG_MATOM results in countless warnings from objtool, such as

arch/x86/events/intel/ds.o: warning: objtool: intel_pmu_pebs_del()+0x43: call without frame pointer save/setup
security/keys/keyring.o: warning: objtool: keyring_read()+0x59: call without frame pointer save/setup
kernel/signal.o: warning: objtool: __dequeue_signal()+0xd8: call without frame pointer save/setup
kernel/signal.o: warning: objtool: kill_pid()+0x15: call without frame pointer save/setup
kernel/signal.o: warning: objtool: SyS_signal()+0x27: call without frame pointer save/setup
mm/page_alloc.o: warning: objtool: zone_watermark_ok_safe()+0x27: call without frame pointer save/setup
fs/exec.o: warning: objtool: read_code()+0x18: call without frame pointer save/setup
mm/swap.o: warning: objtool: get_kernel_page()+0x24: call without frame pointer save/setup
mm/swap.o: warning: objtool: pagevec_move_tail.constprop.25()+0x26: call without frame pointer save/setup
block/bio.o: warning: objtool: bio_map_kern()+0x47: call without frame pointer save/setup
arch/x86/crypto/poly1305_glue.o: warning: objtool: poly1305_simd_mult()+0x2d: call without frame pointer save/setup
crypto/skcipher.o: warning: objtool: skcipher_encrypt_ablkcipher()+0x58: call without frame pointer save/setup
crypto/skcipher.o: warning: objtool: skcipher_decrypt_ablkcipher()+0x58: call without frame pointer save/setup
fs/inode.o: warning: objtool: ilookup()+0x5d: call without frame pointer save/setup
fs/inode.o: warning: objtool: proc_nr_inodes()+0x3e: call without frame pointer save/setup
fs/namei.o: warning: objtool: lookup_one_len_unlocked()+0x21: call without frame pointer save/setup
block/elevator.o: warning: objtool: elv_rb_add()+0x5b: call without frame pointer save/setup
crypto/shash.o: warning: objtool: shash_async_init()+0x1e: call without frame pointer save/setup
crypto/shash.o: warning: objtool: shash_async_import()+0x1e: call without frame pointer save/setup
mm/vmscan.o: warning: objtool: pfmemalloc_watermark_ok()+0xb9: call without frame pointer save/setup

I have not looked at whether this is a bug in gcc or in objtool, however
I found that not using -mtune=atom reliably avoids the problem. I could
reproduce the problem with gcc versions 4.7 through 6.1.

Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 2d449337a360..e1dfb37d66ad 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -110,7 +110,7 @@ else
         cflags-$(CONFIG_MCORE2) += \
                 $(call cc-option,-march=core2,$(call cc-option,-mtune=generic))
 	cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
-		$(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
+		$(call cc-option,-mtune=generic)
         cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=generic)
         KBUILD_CFLAGS += $(cflags-y)
 
-- 
2.9.0