Re: [PATCH 1/4] Remove read_memory_string

[Pedro Alves <palves@redhat.com>]

On 6/12/20 10:53 PM, Tom Tromey wrote:
> read_memory_string is redundant and only called in a couple of spots.
> This patch removes it in favor of target_read_string.
> 

There's a difference of behavior that is getting lost here -- read_memory_string
throws an error on memory read failure, while target_read_string does not.

Similarly to how we have read_memory throwing, vs target_read_memory not
throwing.  It would make sense to me to reimplement read_memory_string on top
of target_read_string and throw on error, for instance.

Did you go over the call paths, to check whether the behavior change
is desirable?

Thanks,
Pedro Alves

> gdb/ChangeLog
> 2020-06-02  Tom Tromey  <tromey@adacore.com>
> 
> 	* corefile.c (read_memory_string): Remove.
> 	* ada-valprint.c (ada_value_print_ptr): Update.
> 	* ada-lang.h (ada_tag_name): Change return type.
> 	* ada-lang.c (type_from_tag): Update.
> 	(ada_tag_name_from_tsd): Change return type.  Use
> 	target_read_string.
> 	(ada_tag_name): Likewise.
> 	* gdbcore.h (read_memory_string): Don't declare.
> ---
>  gdb/ChangeLog      | 11 +++++++++++
>  gdb/ada-lang.c     | 34 ++++++++++++++++++++--------------
>  gdb/ada-lang.h     |  2 +-
>  gdb/ada-valprint.c |  4 ++--
>  gdb/corefile.c     | 27 ---------------------------
>  gdb/gdbcore.h      |  6 ------
>  6 files changed, 34 insertions(+), 50 deletions(-)
> 
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index f7b973f36ee..3245758a1bd 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -6567,10 +6567,10 @@ value_tag_from_contents_and_address (struct type *type,
>  static struct type *
>  type_from_tag (struct value *tag)
>  {
> -  const char *type_name = ada_tag_name (tag);
> +  gdb::unique_xmalloc_ptr<char> type_name = ada_tag_name (tag);
>  
>    if (type_name != NULL)
> -    return ada_find_any_type (ada_encode (type_name));
> +    return ada_find_any_type (ada_encode (type_name.get ()));
>    return NULL;
>  }
>  
> @@ -6721,34 +6721,38 @@ ada_get_tsd_from_tag (struct value *tag)
>     The returned value is good until the next call.  May return NULL
>     if we are unable to determine the tag name.  */
>  
> -static char *
> +static gdb::unique_xmalloc_ptr<char>
>  ada_tag_name_from_tsd (struct value *tsd)
>  {
> -  static char name[1024];
>    char *p;
>    struct value *val;
>  
>    val = ada_value_struct_elt (tsd, "expanded_name", 1);
>    if (val == NULL)
>      return NULL;
> -  read_memory_string (value_as_address (val), name, sizeof (name) - 1);
> -  for (p = name; *p != '\0'; p += 1)
> +  gdb::unique_xmalloc_ptr<char> buffer;
> +  int err;
> +  if (target_read_string (value_as_address (val), &buffer, INT_MAX, &err) == 0
> +      || err != 0)
> +    return nullptr;
> +
> +  for (p = (char *) buffer.get (); *p != '\0'; p += 1)
>      if (isalpha (*p))
>        *p = tolower (*p);
> -  return name;
> +
> +  return buffer;
>  }
>  
>  /* The type name of the dynamic type denoted by the 'tag value TAG, as
>     a C string.
>  
>     Return NULL if the TAG is not an Ada tag, or if we were unable to
> -   determine the name of that tag.  The result is good until the next
> -   call.  */
> +   determine the name of that tag.  */
>  
> -const char *
> +gdb::unique_xmalloc_ptr<char>
>  ada_tag_name (struct value *tag)
>  {
> -  char *name = NULL;
> +  gdb::unique_xmalloc_ptr<char> name;
>  
>    if (!ada_is_tag_type (value_type (tag)))
>      return NULL;
> @@ -12104,9 +12108,11 @@ ada_exception_message_1 (void)
>    if (e_msg_len <= 0)
>      return NULL;
>  
> -  gdb::unique_xmalloc_ptr<char> e_msg ((char *) xmalloc (e_msg_len + 1));
> -  read_memory_string (value_address (e_msg_val), e_msg.get (), e_msg_len + 1);
> -  e_msg.get ()[e_msg_len] = '\0';
> +  gdb::unique_xmalloc_ptr<char> e_msg;
> +  int err;
> +  if (target_read_string (value_address (e_msg_val), &e_msg, INT_MAX, &err) == 0
> +      || err != 0)
> +    return nullptr;
>  
>    return e_msg;
>  }
> diff --git a/gdb/ada-lang.h b/gdb/ada-lang.h
> index 5ba00518e6d..9be597942fd 100644
> --- a/gdb/ada-lang.h
> +++ b/gdb/ada-lang.h
> @@ -260,7 +260,7 @@ extern int ada_is_tagged_type (struct type *, int);
>  
>  extern int ada_is_tag_type (struct type *);
>  
> -extern const char *ada_tag_name (struct value *);
> +extern gdb::unique_xmalloc_ptr<char> ada_tag_name (struct value *);
>  
>  extern struct value *ada_tag_value_at_base_address (struct value *obj);
>  
> diff --git a/gdb/ada-valprint.c b/gdb/ada-valprint.c
> index a36e7ca793a..61893d5cad3 100644
> --- a/gdb/ada-valprint.c
> +++ b/gdb/ada-valprint.c
> @@ -754,10 +754,10 @@ ada_value_print_ptr (struct value *val,
>    struct type *type = ada_check_typedef (value_type (val));
>    if (ada_is_tag_type (type))
>      {
> -      const char *name = ada_tag_name (val);
> +      gdb::unique_xmalloc_ptr<char> name = ada_tag_name (val);
>  
>        if (name != NULL)
> -	fprintf_filtered (stream, " (%s)", name);
> +	fprintf_filtered (stream, " (%s)", name.get ());
>      }
>  }
>  
> diff --git a/gdb/corefile.c b/gdb/corefile.c
> index 996e5301b27..fed0e4fe8ad 100644
> --- a/gdb/corefile.c
> +++ b/gdb/corefile.c
> @@ -328,33 +328,6 @@ read_code_unsigned_integer (CORE_ADDR memaddr, int len,
>    return extract_unsigned_integer (buf, len, byte_order);
>  }
>  
> -void
> -read_memory_string (CORE_ADDR memaddr, char *buffer, int max_len)
> -{
> -  char *cp;
> -  int i;
> -  int cnt;
> -
> -  cp = buffer;
> -  while (1)
> -    {
> -      if (cp - buffer >= max_len)
> -	{
> -	  buffer[max_len - 1] = '\0';
> -	  break;
> -	}
> -      cnt = max_len - (cp - buffer);
> -      if (cnt > 8)
> -	cnt = 8;
> -      read_memory (memaddr + (int) (cp - buffer), (gdb_byte *) cp, cnt);
> -      for (i = 0; i < cnt && *cp; i++, cp++)
> -	;			/* null body */
> -
> -      if (i < cnt && !*cp)
> -	break;
> -    }
> -}
> -
>  CORE_ADDR
>  read_memory_typed_address (CORE_ADDR addr, struct type *type)
>  {
> diff --git a/gdb/gdbcore.h b/gdb/gdbcore.h
> index 24db21e462c..58566d58785 100644
> --- a/gdb/gdbcore.h
> +++ b/gdb/gdbcore.h
> @@ -87,12 +87,6 @@ extern ULONGEST read_code_unsigned_integer (CORE_ADDR memaddr,
>  					    int len,
>  					    enum bfd_endian byte_order);
>  
> -/* Read a null-terminated string from the debuggee's memory, given
> -   address, a buffer into which to place the string, and the maximum
> -   available space.  */
> -
> -extern void read_memory_string (CORE_ADDR, char *, int);
> -
>  /* Read the pointer of type TYPE at ADDR, and return the address it
>     represents.  */
>  
>