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Subject[PATCH v5 mips-next 4/9] MIPS: properly stop .eh_frame generation
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>

+#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 .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) \
+ CFI_SECTIONS; \
.globl symbol; \
.align 2; \
.type symbol, @function; \
@@ -36,6 +53,7 @@ symbol: .frame sp, 0, ra; \
* NESTED - declare nested routine entry point
*/
#define NESTED(symbol, framesize, rpc) \
+ CFI_SECTIONS; \
.globl symbol; \
.align 2; \
.type symbol, @function; \
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
*(.options)
*(.pdr)
*(.reginfo)
- *(.eh_frame)
}
}
--
2.30.0

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