Merge branch 'x86-cleanups-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-2.6-microblaze.git] / Documentation / x86 / exception-tables.rst

diff --git a/Documentation/x86/exception-tables.rst b/Documentation/x86/exception-tables.rst
index 514f518..de58110 100644 (file)
--- a/Documentation/x86/exception-tables.rst
+++ b/Documentation/x86/exception-tables.rst
@@ -257,6 +257,9 @@ the fault, in our case the actual value is c0199ff5:
 the original assembly code: > 3:      movl $-14,%eax
 and linked in vmlinux     : > c0199ff5 <.fixup+10b5> movl   $0xfffffff2,%eax
 
+If the fixup was able to handle the exception, control flow may be returned
+to the instruction after the one that triggered the fault, ie. local label 2b.
+
 The assembly code::
 
  > .section __ex_table,"a"
@@ -338,3 +341,14 @@ pointer which points to one of:
      check.
 
 More functions can easily be added.
+
+CONFIG_BUILDTIME_TABLE_SORT allows the __ex_table section to be sorted post
+link of the kernel image, via a host utility scripts/sorttable. It will set the
+symbol main_extable_sort_needed to 0, avoiding sorting the __ex_table section
+at boot time. With the exception table sorted, at runtime when an exception
+occurs we can quickly lookup the __ex_table entry via binary search.
+
+This is not just a boot time optimization, some architectures require this
+table to be sorted in order to handle exceptions relatively early in the boot
+process. For example, i386 makes use of this form of exception handling before
+paging support is even enabled!