From 13d61012f9b225f2b1749a3de9f0dec66d584a27 Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Thu, 10 Nov 2016 14:04:26 +0000
Subject: [PATCH] create-diff-object: Update fixup offsets in .rela__ex_table

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.

Fixes #615.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
 kpatch-build/create-diff-object.c | 40 +++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index 6c27ba0..d309468 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -1490,6 +1490,31 @@ 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);
+	}
+}
+
 void kpatch_regenerate_special_section(struct kpatch_elf *kelf,
 				       struct special_section *special,
 				       struct section *sec)
@@ -1506,6 +1531,14 @@ 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;
@@ -1533,6 +1566,13 @@ 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);
 			}
 		}