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Diffstat (limited to 'Documentation/x86/exception-tables.rst')
| -rw-r--r-- | Documentation/x86/exception-tables.rst | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/Documentation/x86/exception-tables.rst b/Documentation/x86/exception-tables.rst index ed6d4b0cf62c..de58110c5ffd 100644 --- 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" @@ -337,10 +340,15 @@ pointer which points to one of: entry->insn. It is used to distinguish page faults from machine check. -3) ``int ex_handler_ext(const struct exception_table_entry *fixup)`` - This case is used for uaccess_err ... we need to set a flag - in the task structure. Before the handler functions existed this - case was handled by adding a large offset to the fixup to tag - it as special. - 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! |