x86: Use .cfi_sections for assembly code

The newer assemblers support the .cfi_sections directive so we can put
the CFI from .S files into the .debug_frame section that is preserved
in unstripped vmlinux and in separate debuginfo, rather than the
.eh_frame section that is now discarded by vmlinux.lds.S.

Signed-off-by: Roland McGrath <roland@redhat.com>
LKML-Reference: <20100514044303.A6FE7400BE@magilla.sf.frob.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/Makefile

@@ -95,8 +95,9 @@ sp-$(CONFIG_X86_64) := rsp
 cfi := $(call as-instr,.cfi_startproc\n.cfi_rel_offset $(sp-y)$(comma)0\n.cfi_endproc,-DCONFIG_AS_CFI=1)
 # is .cfi_signal_frame supported too?
 cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)
-KBUILD_AFLAGS += $(cfi) $(cfi-sigframe)
-KBUILD_CFLAGS += $(cfi) $(cfi-sigframe)
+cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)
+KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)
+KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections)
 
 LDFLAGS := -m elf_$(UTS_MACHINE)
 

arch/x86/include/asm/dwarf2.h

@@ -34,6 +34,18 @@
 #define CFI_SIGNAL_FRAME
 #endif
 
+#if defined(CONFIG_AS_CFI_SECTIONS) && defined(__ASSEMBLY__)
+	/*
+	 * Emit CFI data in .debug_frame sections, not .eh_frame sections.
+	 * The latter we currently just discard since we don't do DWARF
+	 * unwinding at runtime.  So only the offline DWARF information is
+	 * useful to anyone.  Note we should not use this directive if this
+	 * file is used in the vDSO assembly, or if vmlinux.lds.S gets
+	 * changed so it doesn't discard .eh_frame.
+	 */
+	.cfi_sections .debug_frame
+#endif
+
 #else
 
 /*