[PATCH] x86-64: Speed up dwarf2 unwinder

This changes the dwarf2 unwinder to do a binary search for CIEs
instead of a linear work. The linker is unfortunately not
able to build a proper lookup table at link time, instead it creates
one at runtime as soon as the bootmem allocator is usable (so you'll continue
using the linear lookup for the first [hopefully] few calls).
The code should be ready to utilize a build-time created table once
a fixed linker becomes available.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

2 files changed, 18 insertions, 0 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 69240b52f8e1..9d0d11c180d9 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -125,6 +125,10 @@
                 *(__param)                                              \
                 VMLINUX_SYMBOL(__stop___param) = .;                     \
         }                                                               \
+                                                                        \
+        /* Unwind data binary search table */                           \
+        EH_FRAME_HDR                                                    \
+                                                                        \
         __end_rodata = .;                                               \
         . = ALIGN(4096);
 
@@ -157,6 +161,18 @@
                 *(.kprobes.text)                                        \
                 VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
+#ifdef CONFIG_STACK_UNWIND
+                /* Unwind data binary search table */
+#define EH_FRAME_HDR                                                    \
+                .eh_frame_hdr : AT(ADDR(.eh_frame_hdr) - LOAD_OFFSET) { \
+                        VMLINUX_SYMBOL(__start_unwind_hdr) = .;         \
+                        *(.eh_frame_hdr)                                \
+                        VMLINUX_SYMBOL(__end_unwind_hdr) = .;           \
+                }
+#else
+#define EH_FRAME_HDR
+#endif
+
                 /* DWARF debug sections.
                 Symbols in the DWARF debugging sections are relative to
                 the beginning of the section so we begin them at 0.  */
diff --git a/include/linux/unwind.h b/include/linux/unwind.h
index 73e1751d03dd..749928c161fb 100644
--- a/include/linux/unwind.h
+++ b/include/linux/unwind.h
@@ -26,6 +26,7 @@ struct module;
  * Initialize unwind support.
  */
 extern void unwind_init(void);
+extern void unwind_setup(void);
 
 #ifdef CONFIG_MODULES
 
@@ -73,6 +74,7 @@ extern int unwind_to_user(struct unwind_frame_info *);
 struct unwind_frame_info {};
 
 static inline void unwind_init(void) {}
+static inline void unwind_setup(void) {}
 
 #ifdef CONFIG_MODULES