Change target_read_string API

This simplifies the target_read_string API a bit.

Note that some code was using safe_strerror on the error codes
returned by target_read_string.  It seems to me that this is incorrect
(if it was ever correct, it must have been quite a long time ago).

gdb/ChangeLog
2020-06-15  Tom Tromey  <tromey@adacore.com>

	* windows-nat.c (windows_nat::handle_output_debug_string):
	Update.
	(windows_nat::handle_ms_vc_exception): Update.
	* target.h (target_read_string): Change API.
	* target.c (target_read_string): Change API.
	* solib-svr4.c (open_symbol_file_object, svr4_read_so_list):
	Update.
	* solib-frv.c (frv_current_sos): Update.
	* solib-dsbt.c (dsbt_current_sos): Update.
	* solib-darwin.c (darwin_current_sos): Update.
	* linux-thread-db.c (inferior_has_bug): Update.
	* expprint.c (print_subexp_standard): Update.
	* ada-lang.c (ada_main_name, ada_tag_name_from_tsd)
	(ada_exception_message_1): Update.

1 files changed, 11 insertions, 15 deletions

diff --git a/gdb/target.c b/gdb/target.c
index 897b8fd..e8193b4 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -804,28 +804,24 @@ target_xfer_status_to_string (enum target_xfer_status status)
 };
 
 
-/* target_read_string -- read a null terminated string, up to LEN bytes,
-   from MEMADDR in target.  Set *ERRNOP to the errno code, or 0 if successful.
-   Set *STRING to a pointer to malloc'd memory containing the data; the caller
-   is responsible for freeing it.  Return the number of bytes successfully
-   read.  */
+/* See target.h.  */
 
-int
-target_read_string (CORE_ADDR memaddr, gdb::unique_xmalloc_ptr<char> *string,
-		    int len, int *errnop)
+gdb::unique_xmalloc_ptr<char>
+target_read_string (CORE_ADDR memaddr, int len, int *bytes_read)
 {
-  int bytes_read;
   gdb::unique_xmalloc_ptr<gdb_byte> buffer;
 
+  int ignore;
+  if (bytes_read == nullptr)
+    bytes_read = &ignore;
+
   /* Note that the endian-ness does not matter here.  */
   int errcode = read_string (memaddr, -1, 1, len, BFD_ENDIAN_LITTLE,
-			     &buffer, &bytes_read);
-
-  if (errnop != nullptr)
-    *errnop = errcode;
+			     &buffer, bytes_read);
+  if (errcode != 0)
+    return {};
 
-  string->reset ((char *) buffer.release ());
-  return bytes_read;
+  return gdb::unique_xmalloc_ptr<char> ((char *) buffer.release ());
 }
 
 struct target_section_table *