[PATCH v2] Fix: Sign extensions for DW_FORM_addrx were never considered

[Can Acar <canacar@imcan.dev>]

From: "canacar@imcan.dev" <canacar@imcan.dev>

DW_FORM_addr is converted (sign-extended) to a signed value when
the dwarf size is less than the size of unrelocated_addr, if the
target architecture "naturally" sign extends an address (bfd.c).

However, the same handling was not done for DW_FORM_addrx. This
meant that for example, trying to `list` a function with an
address >= 0x80000000 on (some?) 32-bit mips targets, when
that address was encoded using DW_FORM_addrx, was broken.

This patch fixes this issue by plumbing read_addr_index_1 into
unit_head::read_address, which is the function used to extract
information from DW_FORM_addr, and so it handles this case
correctly.
---
Changes since v1:
  * read_addr_index_1 has been removed, merging its functionality into
  read_addr_index.
  * dwarf2_read_addr_index has been modified to change the reference to the cu
  in the newly-created cu case to something that seems safer.
  * fix a formatting issue in a call to read_address.

 gdb/dwarf2/read.c | 44 ++++++++++++++++----------------------------
 1 file changed, 16 insertions(+), 28 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 431b7c9ea2c..cca42722471 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -15352,14 +15352,20 @@ dwarf2_per_objfile::read_line_string (const gdb_byte *buf,
    ADDR_BASE is the DW_AT_addr_base (DW_AT_GNU_addr_base) attribute or zero.
    ADDR_SIZE is the size of addresses from the CU header.  */
 
+/* Given index ADDR_INDEX in .debug_addr, fetch the value.  */
+
 static unrelocated_addr
-read_addr_index_1 (dwarf2_per_objfile *per_objfile, unsigned int addr_index,
-		   std::optional<ULONGEST> addr_base, int addr_size)
+read_addr_index (struct dwarf2_cu *cu, unsigned int addr_index)
 {
+  const gdb_byte *info_ptr;
+  struct dwarf2_per_objfile *per_objfile = cu->per_objfile;
+  std::optional<ULONGEST> addr_base = cu->addr_base;
+  struct unit_head *cu_header = &cu->header;
   struct objfile *objfile = per_objfile->objfile;
   bfd *abfd = objfile->obfd.get ();
-  const gdb_byte *info_ptr;
   ULONGEST addr_base_or_zero = addr_base.has_value () ? *addr_base : 0;
+  unsigned int ignore_bytes_read;
+  unsigned char addr_size = cu_header->addr_size;
 
   per_objfile->per_bfd->addr.read (objfile);
   if (per_objfile->per_bfd->addr.buffer == NULL)
@@ -15372,20 +15378,9 @@ read_addr_index_1 (dwarf2_per_objfile *per_objfile, unsigned int addr_index,
 	   objfile_name (objfile));
   info_ptr = (per_objfile->per_bfd->addr.buffer + addr_base_or_zero
 	      + addr_index * addr_size);
-  if (addr_size == 4)
-    return (unrelocated_addr) bfd_get_32 (abfd, info_ptr);
-  else
-    return (unrelocated_addr) bfd_get_64 (abfd, info_ptr);
+  return cu_header->read_address (abfd, info_ptr, &ignore_bytes_read);
 }
 
-/* Given index ADDR_INDEX in .debug_addr, fetch the value.  */
-
-static unrelocated_addr
-read_addr_index (struct dwarf2_cu *cu, unsigned int addr_index)
-{
-  return read_addr_index_1 (cu->per_objfile, addr_index,
-			    cu->addr_base, cu->header.addr_size);
-}
 
 /* Given a pointer to an leb128 value, fetch the value from .debug_addr.  */
 
@@ -15405,11 +15400,10 @@ unrelocated_addr
 dwarf2_read_addr_index (dwarf2_per_cu *per_cu, dwarf2_per_objfile *per_objfile,
 			unsigned int addr_index)
 {
+  std::optional<cutu_reader> reader;
   struct dwarf2_cu *cu = per_objfile->get_cu (per_cu);
-  std::optional<ULONGEST> addr_base;
-  int addr_size;
 
-  /* We need addr_base and addr_size.
+  /* read_addr_index requires some fields from cu.
      If we don't have PER_CU->cu, we have to get it.
      Nasty, but the alternative is storing the needed info in PER_CU,
      which at this point doesn't seem justified: it's not clear how frequently
@@ -15425,20 +15419,14 @@ dwarf2_read_addr_index (dwarf2_per_cu *per_cu, dwarf2_per_objfile *per_objfile,
      IWBN to use the aging mechanism to let us lazily later discard the CU.
      For now we skip this optimization.  */
 
-  if (cu != NULL)
+  if (cu == NULL)
     {
-      addr_base = cu->addr_base;
-      addr_size = cu->header.addr_size;
-    }
-  else
-    {
-      cutu_reader reader (*per_cu, *per_objfile, nullptr, nullptr, false,
+      reader.emplace (*per_cu, *per_objfile, nullptr, nullptr, false,
 			  language_minimal);
-      addr_base = reader.cu ()->addr_base;
-      addr_size = reader.cu ()->header.addr_size;
+      cu = reader->cu ();
     }
 
-  return read_addr_index_1 (per_objfile, addr_index, addr_base, addr_size);
+  return read_addr_index (cu, addr_index);
 }
 
 /* Given a DW_FORM_GNU_str_index value STR_INDEX, fetch the string.
-- 
2.50.1 (Apple Git-155)