[Xen-devel] [PATCH v2] create-diff-object: Update fixup offsets in .rela.ex_table

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

When pruning entries from the fixup table, update the offsets in
.rela.ex_table otherwise the relas might point to the wrong fixup entry
or even out of the .fixup section.

This is a port of kpatch's commit 13d61012f9b2 ("create-diff-object:
Update fixup offsets in .rela__ex_table").

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---

Changed in v2:
* Updated to match the patch which went into kpatch.

 create-diff-object.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/create-diff-object.c b/create-diff-object.c
index b0d1348..f07e727 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -1057,6 +1057,31 @@ static int should_keep_rela_group(struct section *sec, 
int start, int size)
        return found;
 }
 
+/*
+ * When updating .fixup, the corresponding addends in .ex_table need to be
+ * updated too. Stash the result in rela.r_addend so that the calculation in
+ * fixup_group_size() is not affected.
+ */
+void kpatch_update_ex_table_addend(struct kpatch_elf *kelf,
+                                  struct special_section *special,
+                                  int src_offset, int dest_offset,
+                                  int group_size)
+{
+       struct rela *rela;
+       struct section *sec;
+
+       sec = find_section_by_name(&kelf->sections, ".rela.ex_table");
+       if (!sec)
+               ERROR("missing .rela.ex_table section");
+
+       list_for_each_entry(rela, &sec->relas, list) {
+               if (!strcmp(rela->sym->name, ".fixup") &&
+                   rela->addend >= src_offset &&
+                   rela->addend < src_offset + group_size)
+                       rela->rela.r_addend = rela->addend - (src_offset - 
dest_offset);
+       }
+}
+
 static void kpatch_regenerate_special_section(struct kpatch_elf *kelf,
                                              struct special_section *special,
                                              struct section *sec)
@@ -1073,6 +1098,14 @@ static void kpatch_regenerate_special_section(struct 
kpatch_elf *kelf,
        if (!dest)
                ERROR("malloc");
 
+       /* Restore the stashed r_addend from kpatch_update_ex_table_addend. */
+       if (!strcmp(special->name, ".ex_table")) {
+               list_for_each_entry(rela, &sec->relas, list) {
+                       if (!strcmp(rela->sym->name, ".fixup"))
+                               rela->addend = rela->rela.r_addend;
+               }
+       }
+
        group_size = 0;
        src_offset = 0;
        dest_offset = 0;
@@ -1100,6 +1133,12 @@ static void kpatch_regenerate_special_section(struct 
kpatch_elf *kelf,
                                rela->rela.r_offset = rela->offset;
 
                                rela->sym->include = 1;
+
+                               if (!strcmp(special->name, ".fixup"))
+                                       kpatch_update_ex_table_addend(kelf, 
special,
+                                                                     
src_offset,
+                                                                     
dest_offset,
+                                                                     
group_size);
                        }
                }
 
-- 
2.7.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel