[PATCH] Make elf section sorting more deterministic

[Ulf Hermann <ulf.hermann@qt.io>]

At least one test (dwfl-addr-sect) depends on the order of elf sections
with equal addresses. This is not guaranteed by the code. Compare also
by end address and name to tell entries apart.

Signed-off-by: Ulf Hermann <ulf.hermann@qt.io>
---
 libdwfl/ChangeLog           |  5 +++++
 libdwfl/derelocate.c        | 17 +++++++++++------
 tests/ChangeLog             |  6 ++++++
 tests/run-dwfl-addr-sect.sh |  2 +-
 4 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index f605f46..a1ed675 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,5 +1,10 @@
 2017-04-20  Ulf Hermann  <ulf.hermann@qt.io>
 
+	* derelocate.c (compare_secrefs): Compare by end address and then by
+	name if start addresses are equal.
+
+2017-04-20  Ulf Hermann  <ulf.hermann@qt.io>
+
 	* elf-from-memory.c: Explicitly cast phnum to size_t.
 
 2017-04-20  Ulf Hermann  <ulf.hermann@qt.io>
diff --git a/libdwfl/derelocate.c b/libdwfl/derelocate.c
index e5c3e12..8d965af 100644
--- a/libdwfl/derelocate.c
+++ b/libdwfl/derelocate.c
@@ -57,17 +57,22 @@ struct secref
 static int
 compare_secrefs (const void *a, const void *b)
 {
-  struct secref *const *p1 = a;
-  struct secref *const *p2 = b;
+  struct secref const *p1 = *(struct secref *const *)a;
+  struct secref const *p2 = *(struct secref *const *)b;
 
   /* No signed difference calculation is correct here, since the
      terms are unsigned and could be more than INT64_MAX apart.  */
-  if ((*p1)->start < (*p2)->start)
+  if (p1->start < p2->start)
     return -1;
-  if ((*p1)->start > (*p2)->start)
+  if (p1->start > p2->start)
     return 1;
-
-  return 0;
+  if (p1->end < p2->end)
+    return -1;
+  if (p1->end > p2->end)
+    return 1;
+  if (p1->name == NULL)
+    return p2->name == NULL ? 0 : -1;
+  return p2->name == NULL ? 1 : strcmp(p1->name, p2->name);
 }
 
 static int
diff --git a/tests/ChangeLog b/tests/ChangeLog
index c4e76d1..4da049b 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,5 +1,11 @@
 2017-04-20  Ulf Hermann <ulf.hermann@qt.io>
 
+	* run-dwfl-addr-sect.sh: Expect section with alphabetically smaller
+	name when requesting the start address of two otherwise equal
+	zero-sized sections.
+
+2017-04-20  Ulf Hermann <ulf.hermann@qt.io>
+
 	* run-readelf-dwz-multi.sh: Expect readelf to output "yes" for flags
 	that are set.
 	* run-readelf-zdebug-rel.sh: Likewise.
diff --git a/tests/run-dwfl-addr-sect.sh b/tests/run-dwfl-addr-sect.sh
index 80da008..e257bfc 100755
--- a/tests/run-dwfl-addr-sect.sh
+++ b/tests/run-dwfl-addr-sect.sh
@@ -20,7 +20,7 @@
 testfiles testfile43 testfile50
 
 testrun_compare ${abs_builddir}/dwfl-addr-sect -e testfile43 0x64 0x8 0x98 <<\EOF
-address 0x64 => module "" section 4 + 0
+address 0x64 => module "" section 3 + 0
 address 0x8 => module "" section 1 + 0x8
 address 0x98 => module "" section 7 + 0
 EOF
-- 
2.1.4