libdw: set address size, offset size and version on fake CUsfake_cu_elf_addr_size

There are three "fake CUs" that are associated with .debug_loc,
.debug_loclist and .debug_addr.  These fake CUs are used for "fake
attributes" to provide values that are stored in these sections
instead of in the .debug_info section. These fake CUs didn't have the
address size, offset size and DWARF version set. This meant that
values that depended on those properties might not be interpreted
correctly. One example was the value associated with a DW_OP_addrx
(which comes from the .debug_addr section).

Add a testcase using varlocs to test that addresses can correctly be
retrieved for gcc/clang, DWARF4/5 and 32/64 bits objects.

https://sourceware.org/bugzilla/show_bug.cgi?id=28220

Signed-off-by: Mark Wielaard <mark@klomp.org>

1 files changed, 26 insertions, 6 deletions

diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
index 9e944b86..a368feb8 100644
--- a/libdw/dwarf_begin_elf.c
+++ b/libdw/dwarf_begin_elf.c
@@ -224,6 +224,23 @@ valid_p (Dwarf *result)
       result = NULL;
     }
 
+  /* We are setting up some "fake" CUs, which need an address size.
+     Check the ELF class to come up with something reasonable.  */
+  int elf_addr_size = 8;
+  if (result != NULL)
+    {
+      GElf_Ehdr ehdr;
+      if (gelf_getehdr (result->elf, &ehdr) == NULL)
+        {
+          Dwarf_Sig8_Hash_free (&result->sig8_hash);
+          __libdw_seterrno (DWARF_E_INVALID_ELF);
+          free (result);
+          result = NULL;
+        }
+      else if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+        elf_addr_size = 4;
+    }
+
   /* For dwarf_location_attr () we need a "fake" CU to indicate
      where the "fake" attribute data comes from.  This is a block
      inside the .debug_loc or .debug_loclists section.  */
@@ -247,8 +264,9 @@ valid_p (Dwarf *result)
             = (result->sectiondata[IDX_debug_loc]->d_buf
                + result->sectiondata[IDX_debug_loc]->d_size);
           result->fake_loc_cu->locs = NULL;
-          result->fake_loc_cu->address_size = 0;
-          result->fake_loc_cu->version = 0;
+          result->fake_loc_cu->address_size = elf_addr_size;
+          result->fake_loc_cu->offset_size = 4;
+          result->fake_loc_cu->version = 4;
           result->fake_loc_cu->split = NULL;
         }
     }
@@ -274,8 +292,9 @@ valid_p (Dwarf *result)
             = (result->sectiondata[IDX_debug_loclists]->d_buf
                + result->sectiondata[IDX_debug_loclists]->d_size);
           result->fake_loclists_cu->locs = NULL;
-          result->fake_loclists_cu->address_size = 0;
-          result->fake_loclists_cu->version = 0;
+          result->fake_loclists_cu->address_size = elf_addr_size;
+          result->fake_loclists_cu->offset_size = 4;
+          result->fake_loclists_cu->version = 5;
           result->fake_loclists_cu->split = NULL;
         }
     }
@@ -306,8 +325,9 @@ valid_p (Dwarf *result)
             = (result->sectiondata[IDX_debug_addr]->d_buf
                + result->sectiondata[IDX_debug_addr]->d_size);
           result->fake_addr_cu->locs = NULL;
-          result->fake_addr_cu->address_size = 0;
-          result->fake_addr_cu->version = 0;
+          result->fake_addr_cu->address_size = elf_addr_size;
+          result->fake_addr_cu->offset_size = 4;
+          result->fake_addr_cu->version = 5;
           result->fake_addr_cu->split = NULL;
         }
     }