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Date:   Sun, 10 Jan 2021 11:56:28 +0000
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
From:   Alexander Lobakin <alobakin@pm.me>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Pei Huang <huangpei@loongson.cn>,
        Kees Cook <keescook@chromium.org>,
        Alexander Lobakin <alobakin@pm.me>,
        Fangrui Song <maskray@google.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Corey Minyard <cminyard@mvista.com>,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, stable@vger.kernel.org,
        clang-built-linux@googlegroups.com
Reply-To: Alexander Lobakin <alobakin@pm.me>
Subject: [PATCH v5 mips-next 4/9] MIPS: properly stop .eh_frame generation
Message-ID: <20210110115546.30970-4-alobakin@pm.me>
In-Reply-To: <20210110115546.30970-1-alobakin@pm.me>
References: <20210110115245.30762-1-alobakin@pm.me> <20210110115546.30970-1-alobakin@pm.me>
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Commit 866b6a89c6d1 ("MIPS: Add DWARF unwinding to assembly") added
-fno-asynchronous-unwind-tables to KBUILD_CFLAGS to prevent compiler
from emitting .eh_frame symbols.
However, as MIPS heavily uses CFI, that's not enough. Use the
approach taken for x86 (as it also uses CFI) and explicitly put CFI
symbols into the .debug_frame section (except for VDSO).
This allows us to drop .eh_frame from DISCARDS as it's no longer
being generated.

Fixes: 866b6a89c6d1 ("MIPS: Add DWARF unwinding to assembly")
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/mips/include/asm/asm.h    | 18 ++++++++++++++++++
 arch/mips/kernel/vmlinux.lds.S |  1 -
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/asm.h b/arch/mips/include/asm/asm.h
index 3682d1a0bb80..ea4b62ece336 100644
--- a/arch/mips/include/asm/asm.h
+++ b/arch/mips/include/asm/asm.h
@@ -20,10 +20,27 @@
 #include <asm/sgidefs.h>
 #include <asm/asm-eva.h>
=20
+#ifndef __VDSO__
+/*
+ * Emit CFI data in .debug_frame sections, not .eh_frame sections.
+ * We don't do DWARF unwinding at runtime, so only the offline DWARF
+ * information is useful to anyone. Note we should change this if we
+ * ever decide to enable DWARF unwinding at runtime.
+ */
+#define CFI_SECTIONS=09.cfi_sections .debug_frame
+#else
+ /*
+  * For the vDSO, emit both runtime unwind information and debug
+  * symbols for the .dbg file.
+  */
+#define CFI_SECTIONS
+#endif
+
 /*
  * LEAF - declare leaf routine
  */
 #define LEAF(symbol)=09=09=09=09=09\
+=09=09CFI_SECTIONS;=09=09=09=09\
 =09=09.globl=09symbol;=09=09=09=09\
 =09=09.align=092;=09=09=09=09\
 =09=09.type=09symbol, @function;=09=09\
@@ -36,6 +53,7 @@ symbol:=09=09.frame=09sp, 0, ra;=09=09=09\
  * NESTED - declare nested routine entry point
  */
 #define NESTED(symbol, framesize, rpc)=09=09=09\
+=09=09CFI_SECTIONS;=09=09=09=09\
 =09=09.globl=09symbol;=09=09=09=09\
 =09=09.align=092;=09=09=09=09\
 =09=09.type=09symbol, @function;=09=09\
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.=
S
index 09669a8fddec..10d8f0dcb76b 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -224,6 +224,5 @@ SECTIONS
 =09=09*(.options)
 =09=09*(.pdr)
 =09=09*(.reginfo)
-=09=09*(.eh_frame)
 =09}
 }
--=20
2.30.0