[PATCH] libdw: dwarf_frame_register takes an array of at least 3 Dwarf_Ops

[Mark Wielaard]

GCC11 will warn about a mismatch in the declaration of dwarf_frame_register:

dwarf_frame_register.c:37:61: error: argument 3 of type ‘Dwarf_Op *’
  declared as a pointer [-Werror=array-parameter=]
   37 | dwarf_frame_register (Dwarf_Frame *fs, int regno, Dwarf_Op *ops_mem,
      |                                                   ~~~~~~~~~~^~~~~~~
libdw.h:1068:43: note: previously declared as an array ‘Dwarf_Op[3]’
 1068 |                                  Dwarf_Op ops_mem[3],
      |                                  ~~~~~~~~~^~~~~~~~~~

When fixing that it will show an actual bug in the addrcfi testcase:

addrcfi.c:98:16: error: ‘dwarf_frame_register’ accessing 96 bytes in a
  region of size 64 [-Werror=stringop-overflow=]
   98 |   int result = dwarf_frame_register (stuff->frame, regno, ops_mem, 
&ops, &nops);
      |                
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
addrcfi.c:98:16: note: referencing argument 3 of type ‘Dwarf_Op *’
 1069 | extern int dwarf_frame_register (Dwarf_Frame *frame, int regno,
      |            ^~~~~~~~~~~~~~~~~~~~

Fix the declaration, fix the bug and add an extra comment to the description
in libdw.h.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 libdw/dwarf_frame_register.c | 2 +-
 libdw/libdw.h                | 8 +++++---
 tests/addrcfi.c              | 2 +-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/libdw/dwarf_frame_register.c b/libdw/dwarf_frame_register.c
index d0159fb8..bcf3fa03 100644
--- a/libdw/dwarf_frame_register.c
+++ b/libdw/dwarf_frame_register.c
@@ -34,7 +34,7 @@
 #include <dwarf.h>
 
 int
-dwarf_frame_register (Dwarf_Frame *fs, int regno, Dwarf_Op *ops_mem,
+dwarf_frame_register (Dwarf_Frame *fs, int regno, Dwarf_Op ops_mem[3],
                      Dwarf_Op **ops, size_t *nops)
 {
   /* Maybe there was a previous error.  */
diff --git a/libdw/libdw.h b/libdw/libdw.h
index 1a4e15a1..ad4fa6ea 100644
--- a/libdw/libdw.h
+++ b/libdw/libdw.h
@@ -1061,9 +1061,11 @@ extern int dwarf_frame_cfa (Dwarf_Frame *frame, Dwarf_Op 
**ops, size_t *nops)
    caller's REGNO is "same_value", i.e. this frame did not change it;
    ask the caller frame where to find it.
 
-   For common simple expressions *OPS is OPS_MEM.  For arbitrary DWARF
-   expressions in the CFI, *OPS is an internal pointer that can be used as
-   long as the Dwarf_CFI used to create FRAME remains alive.  */
+   For common simple expressions *OPS is OPS_MEM (which is a caller
+   owned array for for at least 3 Dwarf_Ops).  For arbitrary DWARF
+   expressions in the CFI, *OPS is an internal pointer that can be
+   used as long as the Dwarf_CFI used to create FRAME remains
+   alive.  */
 extern int dwarf_frame_register (Dwarf_Frame *frame, int regno,
                                 Dwarf_Op ops_mem[3],
                                 Dwarf_Op **ops, size_t *nops)
diff --git a/tests/addrcfi.c b/tests/addrcfi.c
index 589b8513..2b7d7bd0 100644
--- a/tests/addrcfi.c
+++ b/tests/addrcfi.c
@@ -92,7 +92,7 @@ print_register (void *arg,
 
   printf ("\t%s reg%u (%s%s): ", setname, regno, prefix, regname);
 
-  Dwarf_Op ops_mem[2];
+  Dwarf_Op ops_mem[3];
   Dwarf_Op *ops;
   size_t nops;
   int result = dwarf_frame_register (stuff->frame, regno, ops_mem, &ops, 
&nops);
-- 
2.18.4