It may be useful for some tools like gdb or latencytop. So we introduce
CONFIG_UNWIND_INFO. This information is also used by the DWARF unwinder in the
next patches.
In particular, we enable asynchronous unwind tables -- the out-of-band DWARF
info proper. And we also let the linker to generate an index for a fast binary
lookup (eh-frame-hdr).
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kbuild@xxxxxxxxxxxxxxx
---
Makefile | 5 +++++
arch/x86/Makefile | 2 ++
arch/x86/entry/calling.h | 13 +++++++++++++
arch/x86/kernel/vmlinux.lds.S | 2 ++
lib/Kconfig.debug | 10 ++++++++++
5 files changed, 32 insertions(+)
diff --git a/Makefile b/Makefile
index 23cc5d65172b..0eabd1300c69 100644
--- a/Makefile
+++ b/Makefile
@@ -739,6 +739,11 @@ endif
KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments)
+ifdef CONFIG_UNWIND_INFO
+KBUILD_CFLAGS += -fasynchronous-unwind-tables
+LDFLAGS_vmlinux += --eh-frame-hdr
+endif
+
ifdef CONFIG_DEBUG_INFO
ifdef CONFIG_DEBUG_INFO_SPLIT
KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 4430dd489620..a4ab13b383cb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -212,7 +212,9 @@ KBUILD_CFLAGS += -pipe
# Workaround for a gcc prelease that unfortunately was shipped in a suse release
KBUILD_CFLAGS += -Wno-sign-compare
#
+ifneq ($(CONFIG_UNWIND_INFO),y)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
+endif
KBUILD_CFLAGS += $(mflags-y)
KBUILD_AFLAGS += $(mflags-y)
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 05ed3d393da7..fd2334ee62fd 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -48,6 +48,19 @@ For 32-bit we have the following conventions - kernel is built with
*/
+#if !defined(CONFIG_UNWIND_INFO) && 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
+
#ifdef CONFIG_X86_64
/*
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index c8a3b61be0aa..7dfe103d4fae 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -345,7 +345,9 @@ SECTIONS
/* Sections to be discarded */
DISCARDS
/DISCARD/ : {
+#ifndef CONFIG_UNWIND_INFO
*(.eh_frame)
+#endif
}
}
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e4587ebe52c7..e90125b6498e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -45,6 +45,16 @@ config MESSAGE_LOGLEVEL_DEFAULT
by default. To change that, use loglevel=<x> in the kernel bootargs,
or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value.
+config UNWIND_INFO
+ bool "Compile the kernel with frame unwind information"
+ depends on !IA64 && !PARISC && !ARM
+ depends on !MODULES || !(MIPS || PPC || SUPERH || V850)
+ help
+ If you say Y here the resulting kernel image will be slightly larger
+ but not slower, and it will give very useful debugging information.
+ If you don't debug the kernel, you can say N, but we may not be able
+ to solve problems without frame unwind information or frame pointers.
+
config BOOT_PRINTK_DELAY
bool "Delay each boot printk message by N milliseconds"
depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY
--
2.12.2
--
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