[PATCH 1/3] gdb: store internalvars in an std::vector

[PATCH 1/3] gdb: store internalvars in an std::vector

[Simon Marchi]

Change the storage of internalvars to an std::vector of unique pointers
to internalval.  This helps automate memory management, and will help
keep internalvars sorted in a subsequent patch.

I initially tried to use an std::vector<internalval> initially, but some
parts of the code need for the addresses of internalvars to be stable.

Change-Id: I1fca7e7877cc984a3a3432c7639d45e68d437241
---
 gdb/value.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index 7873aeb9558e..e884913abe5a 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1829,7 +1829,6 @@ union internalvar_data
 
 struct internalvar
 {
-  struct internalvar *next;
   char *name;
 
   /* We support various different kinds of content of an internal variable.
@@ -1841,7 +1840,9 @@ struct internalvar
   union internalvar_data u;
 };
 
-static struct internalvar *internalvars;
+using internalvar_up = std::unique_ptr<internalvar>;
+
+static std::vector<internalvar_up> internalvars;
 
 /* If the variable does not already exist create it and give it the
    value given.  If no value is given then the default is zero.  */
@@ -1891,11 +1892,9 @@ init_if_undefined_command (const char* args, int from_tty)
 struct internalvar *
 lookup_only_internalvar (const char *name)
 {
-  struct internalvar *var;
-
-  for (var = internalvars; var; var = var->next)
+  for (internalvar_up &var : internalvars)
     if (strcmp (var->name, name) == 0)
-      return var;
+      return var.get ();
 
   return NULL;
 }
@@ -1906,12 +1905,11 @@ lookup_only_internalvar (const char *name)
 void
 complete_internalvar (completion_tracker &tracker, const char *name)
 {
-  struct internalvar *var;
   int len;
 
   len = strlen (name);
 
-  for (var = internalvars; var; var = var->next)
+  for (internalvar_up &var : internalvars)
     if (strncmp (var->name, name, len) == 0)
       tracker.add_completion (make_unique_xstrdup (var->name));
 }
@@ -1922,12 +1920,12 @@ complete_internalvar (completion_tracker &tracker, const char *name)
 struct internalvar *
 create_internalvar (const char *name)
 {
-  struct internalvar *var = XNEW (struct internalvar);
+  internalvars.emplace_back (new internalvar);
+  internalvar *var = internalvars.back ().get ();
 
   var->name = xstrdup (name);
   var->kind = INTERNALVAR_VOID;
-  var->next = internalvars;
-  internalvars = var;
+
   return var;
 }
 
@@ -2412,8 +2410,6 @@ preserve_one_varobj (struct varobj *varobj, struct objfile *objfile,
 void
 preserve_values (struct objfile *objfile)
 {
-  struct internalvar *var;
-
   /* Create the hash table.  We allocate on the objfile's obstack, since
      it is soon to be deleted.  */
   htab_up copied_types = create_copied_types_hash ();
@@ -2421,8 +2417,8 @@ preserve_values (struct objfile *objfile)
   for (const value_ref_ptr &item : value_history)
     item->preserve (objfile, copied_types.get ());
 
-  for (var = internalvars; var; var = var->next)
-    preserve_one_internalvar (var, objfile, copied_types.get ());
+  for (internalvar_up &var : internalvars)
+    preserve_one_internalvar (var.get (), objfile, copied_types.get ());
 
   /* For the remaining varobj, check that none has type owned by OBJFILE.  */
   all_root_varobjs ([&copied_types, objfile] (struct varobj *varobj)
@@ -2438,14 +2434,12 @@ static void
 show_convenience (const char *ignore, int from_tty)
 {
   struct gdbarch *gdbarch = get_current_arch ();
-  struct internalvar *var;
   int varseen = 0;
   struct value_print_options opts;
 
   get_user_print_options (&opts);
-  for (var = internalvars; var; var = var->next)
+  for (internalvar_up &var : internalvars)
     {
-
       if (!varseen)
 	{
 	  varseen = 1;
@@ -2456,7 +2450,7 @@ show_convenience (const char *ignore, int from_tty)
 	{
 	  struct value *val;
 
-	  val = value_of_internalvar (gdbarch, var);
+	  val = value_of_internalvar (gdbarch, var.get ());
 	  value_print (val, gdb_stdout, &opts);
 	}
       catch (const gdb_exception_error &ex)
-- 
2.39.1

[PATCH 2/3] gdb: use std::string for internalvar::name

[Simon Marchi]

Change internalvar::name to std::string, automating memory management.

Change-Id: I814d61361663e7becb8f3fb5f58c0180cdc414bc
---
 gdb/value.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index e884913abe5a..68499896af8c 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1829,7 +1829,7 @@ union internalvar_data
 
 struct internalvar
 {
-  char *name;
+  std::string name;
 
   /* We support various different kinds of content of an internal variable.
      enum internalvar_kind specifies the kind, and union internalvar_data
@@ -1893,7 +1893,7 @@ struct internalvar *
 lookup_only_internalvar (const char *name)
 {
   for (internalvar_up &var : internalvars)
-    if (strcmp (var->name, name) == 0)
+    if (var->name == name)
       return var.get ();
 
   return NULL;
@@ -1910,8 +1910,8 @@ complete_internalvar (completion_tracker &tracker, const char *name)
   len = strlen (name);
 
   for (internalvar_up &var : internalvars)
-    if (strncmp (var->name, name, len) == 0)
-      tracker.add_completion (make_unique_xstrdup (var->name));
+    if (strncmp (var->name.c_str (), name, len) == 0)
+      tracker.add_completion (make_unique_xstrdup (var->name.c_str ()));
 }
 
 /* Create an internal variable with name NAME and with a void value.
@@ -1923,7 +1923,7 @@ create_internalvar (const char *name)
   internalvars.emplace_back (new internalvar);
   internalvar *var = internalvars.back ().get ();
 
-  var->name = xstrdup (name);
+  var->name = name;
   var->kind = INTERNALVAR_VOID;
 
   return var;
@@ -1994,7 +1994,7 @@ value_of_internalvar (struct gdbarch *gdbarch, struct internalvar *var)
 
   /* If there is a trace state variable of the same name, assume that
      is what we really want to see.  */
-  tsv = find_trace_state_variable (var->name);
+  tsv = find_trace_state_variable (var->name.c_str ());
   if (tsv)
     {
       tsv->value_known = target_get_trace_state_variable_value (tsv->number,
@@ -2147,7 +2147,7 @@ set_internalvar (struct internalvar *var, struct value *val)
   union internalvar_data new_data = { 0 };
 
   if (var->kind == INTERNALVAR_FUNCTION && var->u.fn.canonical)
-    error (_("Cannot overwrite convenience function %s"), var->name);
+    error (_("Cannot overwrite convenience function %s"), var->name.c_str ());
 
   /* Prepare new contents.  */
   switch (check_typedef (val->type ())->code ())
@@ -2259,7 +2259,7 @@ clear_internalvar (struct internalvar *var)
 const char *
 internalvar_name (const struct internalvar *var)
 {
-  return var->name;
+  return var->name.c_str ();
 }
 
 static struct internal_function *
@@ -2444,7 +2444,7 @@ show_convenience (const char *ignore, int from_tty)
 	{
 	  varseen = 1;
 	}
-      gdb_printf (("$%s = "), var->name);
+      gdb_printf (("$%s = "), var->name.c_str ());
 
       try
 	{
-- 
2.39.1

[PATCH 3/3] gdb: keep internalvars sorted

[Simon Marchi]

In a test (downstream in ROCgdb), there was a test case failing when
GDB_REVERSE_INIT_FUNCTIONS was set.  The test was assuming a particular
order in the output of "show convenience".  And the order changed with
GDB_REVERSE_INIT_FUNCTIONS.

I think that a nice way to fix it is to make the output of "show
convenience" sorted, and therefore stable.  Ideally, I think that the
the user-visible behavior of GDB should not change when using
GDB_REVERSE_INIT_FUNCTIONS.  Plus, it makes the output of "show
convenience" look nice, not that it's really important.

So, change create_internalvar to keep the internalvars vector sorted.

Change-Id: I3a916a641e0d50ff698f5d097ef0cf10637ab8de
---
 gdb/value.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index 68499896af8c..2c37f94cba99 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1920,8 +1920,15 @@ complete_internalvar (completion_tracker &tracker, const char *name)
 struct internalvar *
 create_internalvar (const char *name)
 {
-  internalvars.emplace_back (new internalvar);
-  internalvar *var = internalvars.back ().get ();
+  auto it = std::lower_bound (internalvars.begin (),
+			      internalvars.end (),
+			      name,
+			      [] (const internalvar_up &var, const char *name_)
+				{
+				  return var->name < name_;
+				});
+
+  internalvar *var = internalvars.emplace (it, new internalvar)->get ();
 
   var->name = name;
   var->kind = INTERNALVAR_VOID;
-- 
2.39.1

Re: [PATCH 1/3] gdb: store internalvars in an std::vector

[Lancelot SIX]

On Mon, Feb 13, 2023 at 11:21:37PM -0500, Simon Marchi via Gdb-patches wrote:
> Change the storage of internalvars to an std::vector of unique pointers
> to internalval.  This helps automate memory management, and will help
> keep internalvars sorted in a subsequent patch.
> 
> I initially tried to use an std::vector<internalval> initially, but some
> parts of the code need for the addresses of internalvars to be stable.
> 

Hi Simon,

As the end-goal is to have an order, did you consider using a container
which enforces it like a std::map?  For small number of objects (for
some definition of small…) vector is usually more efficient but as here
you hold pointers, I am not sure the vector brings a huge benefit.

You could use a std::map<std::string, internalvar> as the internalvar’s
address will remain stable.  No need to have a unique_ptr.

One downside of the std::map is that you might end up with the name
stored twice (once as key, and maybe still once in the internalvar
object).  std::set can also be used, but with other downsides.

The main difference with vector can come if we had 2 internal variables
with the same name.  The current code does not prevent this AFAICT, but
as one of the vars would effectively shadow the other, I am not sure
this is a case we want to support anyway.

Best,
Lancelot.

> Change-Id: I1fca7e7877cc984a3a3432c7639d45e68d437241
> ---
>  gdb/value.c | 32 +++++++++++++-------------------
>  1 file changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/gdb/value.c b/gdb/value.c
> index 7873aeb9558e..e884913abe5a 100644
> --- a/gdb/value.c
> +++ b/gdb/value.c
> @@ -1829,7 +1829,6 @@ union internalvar_data
>  
>  struct internalvar
>  {
> -  struct internalvar *next;
>    char *name;
>  
>    /* We support various different kinds of content of an internal variable.
> @@ -1841,7 +1840,9 @@ struct internalvar
>    union internalvar_data u;
>  };
>  
> -static struct internalvar *internalvars;
> +using internalvar_up = std::unique_ptr<internalvar>;
> +
> +static std::vector<internalvar_up> internalvars;
>  
>  /* If the variable does not already exist create it and give it the
>     value given.  If no value is given then the default is zero.  */
> @@ -1891,11 +1892,9 @@ init_if_undefined_command (const char* args, int from_tty)
>  struct internalvar *
>  lookup_only_internalvar (const char *name)
>  {
> -  struct internalvar *var;
> -
> -  for (var = internalvars; var; var = var->next)
> +  for (internalvar_up &var : internalvars)
>      if (strcmp (var->name, name) == 0)
> -      return var;
> +      return var.get ();
>  
>    return NULL;
>  }
> @@ -1906,12 +1905,11 @@ lookup_only_internalvar (const char *name)
>  void
>  complete_internalvar (completion_tracker &tracker, const char *name)
>  {
> -  struct internalvar *var;
>    int len;
>  
>    len = strlen (name);
>  
> -  for (var = internalvars; var; var = var->next)
> +  for (internalvar_up &var : internalvars)
>      if (strncmp (var->name, name, len) == 0)
>        tracker.add_completion (make_unique_xstrdup (var->name));
>  }
> @@ -1922,12 +1920,12 @@ complete_internalvar (completion_tracker &tracker, const char *name)
>  struct internalvar *
>  create_internalvar (const char *name)
>  {
> -  struct internalvar *var = XNEW (struct internalvar);
> +  internalvars.emplace_back (new internalvar);
> +  internalvar *var = internalvars.back ().get ();
>  
>    var->name = xstrdup (name);
>    var->kind = INTERNALVAR_VOID;
> -  var->next = internalvars;
> -  internalvars = var;
> +
>    return var;
>  }
>  
> @@ -2412,8 +2410,6 @@ preserve_one_varobj (struct varobj *varobj, struct objfile *objfile,
>  void
>  preserve_values (struct objfile *objfile)
>  {
> -  struct internalvar *var;
> -
>    /* Create the hash table.  We allocate on the objfile's obstack, since
>       it is soon to be deleted.  */
>    htab_up copied_types = create_copied_types_hash ();
> @@ -2421,8 +2417,8 @@ preserve_values (struct objfile *objfile)
>    for (const value_ref_ptr &item : value_history)
>      item->preserve (objfile, copied_types.get ());
>  
> -  for (var = internalvars; var; var = var->next)
> -    preserve_one_internalvar (var, objfile, copied_types.get ());
> +  for (internalvar_up &var : internalvars)
> +    preserve_one_internalvar (var.get (), objfile, copied_types.get ());
>  
>    /* For the remaining varobj, check that none has type owned by OBJFILE.  */
>    all_root_varobjs ([&copied_types, objfile] (struct varobj *varobj)
> @@ -2438,14 +2434,12 @@ static void
>  show_convenience (const char *ignore, int from_tty)
>  {
>    struct gdbarch *gdbarch = get_current_arch ();
> -  struct internalvar *var;
>    int varseen = 0;
>    struct value_print_options opts;
>  
>    get_user_print_options (&opts);
> -  for (var = internalvars; var; var = var->next)
> +  for (internalvar_up &var : internalvars)
>      {
> -
>        if (!varseen)
>  	{
>  	  varseen = 1;
> @@ -2456,7 +2450,7 @@ show_convenience (const char *ignore, int from_tty)
>  	{
>  	  struct value *val;
>  
> -	  val = value_of_internalvar (gdbarch, var);
> +	  val = value_of_internalvar (gdbarch, var.get ());
>  	  value_print (val, gdb_stdout, &opts);
>  	}
>        catch (const gdb_exception_error &ex)
> -- 
> 2.39.1
> 

Re: [PATCH 1/3] gdb: store internalvars in an std::vector

[Simon Marchi]

On 2/14/23 05:54, Lancelot SIX via Gdb-patches wrote:
> On Mon, Feb 13, 2023 at 11:21:37PM -0500, Simon Marchi via Gdb-patches wrote:
>> Change the storage of internalvars to an std::vector of unique pointers
>> to internalval.  This helps automate memory management, and will help
>> keep internalvars sorted in a subsequent patch.
>>
>> I initially tried to use an std::vector<internalval> initially, but some
>> parts of the code need for the addresses of internalvars to be stable.
>>
> 
> Hi Simon,
> 
> As the end-goal is to have an order, did you consider using a container
> which enforces it like a std::map?  For small number of objects (for
> some definition of small…) vector is usually more efficient but as here
> you hold pointers, I am not sure the vector brings a huge benefit.
> 
> You could use a std::map<std::string, internalvar> as the internalvar’s
> address will remain stable.  No need to have a unique_ptr.
> 
> One downside of the std::map is that you might end up with the name
> stored twice (once as key, and maybe still once in the internalvar
> object).  std::set can also be used, but with other downsides.

I had not thought of that, but I think it's a good idea.  Having the
name stored twice is not an issue, I think.

> The main difference with vector can come if we had 2 internal variables
> with the same name.  The current code does not prevent this AFAICT, but
> as one of the vars would effectively shadow the other, I am not sure
> this is a case we want to support anyway.

I don't think it can really happen today anyway.
create_internalvar_type_lazy is only used to create variable known in
advance, for which we know there are no clashes.  And through
lookup_internalvar, create_internalvar is only called after seeing that
there is no variable by that name.  So, I think we'll be fine with a
map.

Simon