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Stack corruption in Ada C binding to OpenGL function

I'm using SDL to retrieve the address of the function. That much seems to be working, since I'm using the same subprogram that's working for all my other function calls.

Here are all the relevant code snippits in the spec:

type GLenum is new Uint32;

subtype glTexImage2D_Target is GLenum with Static_Predicate => glTexImage2D_Target in GL_TEXTURE_2D | GL_TEXTURE_RECTANGLE | GL_PROXY_TEXTURE_RECTANGLE;
subtype glTexImage2D_Dtype is GLenum with Static_Predicate => glTexImage2D_Dtype in GL_BYTE | GL_UNSIGNED_BYTE;
subtype glTexImage2D_InternalFormat is GLenum with Static_Predicate => glTexImage2D_InternalFormat in GL_DEPTH_COMPONENT | GL_DEPTH_STENCIL | GL_RED | GL_RG | GL_RGB | GL_RGBA;
subtype glTexImage2D_Format is GLenum with Static_Predicate => glTexImage2D_Format in GL_RED | GL_RG | GL_RGB | GL_BGR | GL_RGBA | GL_BGRA | GL_RED_INTEGER | GL_RG_INTEGER | GL_RGB_INTEGER | GL_BGR_INTEGER | GL_RGBA_INTEGER | GL_BGRA_INTEGER | GL_STENCIL_INDEX | GL_DEPTH_COMPONENT | GL_DEPTH_STENCIL;

procedure glTexImage2D(target : glTexImage2D_Target; level : Integer; internalFormat : glTexImage2D_InternalFormat; width : Integer; height : Integer; format : glTexImage2D_Format; dtype : glTexImage2D_Dtype; pixels : System.Address) with Pre => (target /= GL_TEXTURE_RECTANGLE and target /= GL_PROXY_TEXTURE_RECTANGLE) or Level = 0;

procedure Set_OpenGL_Subprogram_Address(Addr : in out System.Address; Name : String);

glTexImage2D_C_Address : System.Address := System.Null_Address;

Could_Not_Load_OpenGL_Subprogram : exception;

And here are the relevant snippits in the body:

procedure glTexImage2D(target : glTexImage2D_Target; level : Integer; internalFormat : glTexImage2D_InternalFormat; width : Integer; height : Integer; format : glTexImage2D_Format; dtype : glTexImage2D_Dtype; pixels : System.Address) is
begin
    Set_OpenGL_Subprogram_Address(glTexImage2D_C_Address, "glTexImage2D");
    declare
        procedure glTexImage2D_C(target : GLenum; level : GLint; internalFormat : GLint; width : GLsizei; height : GLsizei; border : GLint; format : GLenum; dtype : GLenum; data : System.Address)
        with Import, Convention => Stdcall, Address => glTexImage2D_C_Address;
    begin
        glTexImage2D_C(GLenum(target), GLint(level), GLint(internalFormat), GLsizei(width), GLsizei(height), GLint'(0), GLenum(format), GLenum(dtype), pixels);
    end;
end glTexImage2D;

--This seems to work... but here it is just in case.
procedure Set_OpenGL_Subprogram_Address(Addr : in out System.Address; Name : String) is
begin
    if Addr = System.Null_Address then
        Addr := SDL_GL_GetProcAddress(Value(New_String(Name)));
        if Addr = System.Null_Address then
            raise Could_Not_Load_OpenGL_Subprogram with Name;
        end if;
    end if;
end Set_OpenGL_Subprogram_Address;

Finally, the pixels I'm passing in is an address indicating an object of type:

type Uc_Array is array(Integer range <>) of aliased Interfaces.C.unsigned_char;

The stack is being corrupted on the call to glTexImage2D_C. I discovered this by using gdb:

enter image description here

Here you can see the parameters I'm passing as well; target 3553, level 0, internalformat 6408, width 63, height 63, format 6408, dtype 5121, non-zero pixels address. The subprogram address is being set to a non-zero value. But after the call to glTexImage2D_C, the value of $sp (the stack pointer) has increased by 16#24#.

I've tried adjusting the height and width I pass to glTexImage2D_C, both to 10 and both to 1000, just to see if giving it more (or less) buffer prevents stack corruption, but in every case, the stack pointer is different before and after the procedure call.

I'm hoping this is a simple matter of an incorrect datatype or something... Here's the prototype of glTexImage2D on the OpenGL side:

void glTexImage2D(  GLenum target,
    GLint level,
    GLint internalformat,
    GLsizei width,
    GLsizei height,
    GLint border,
    GLenum format,
    GLenum type,
    const void * data);

(As a final note, I do intend to clean up the awkward lazy loading tactic you see above, if I can ever get this to actually work. For now I'm leaving it this way so I can eliminate the chance of trying to call a function that hasn't been loaded yet, while I'm still trying to debug the call itself. The tactic of using a nested procedure declared inside a declare...begin...end block is working for other OpenGL functions.)

Wikipedia articles about GNAT

Some Wikipedia articles about GNAT are terribly outdated, for instance:

Perhaps someone will be tempted to give them a brush-up…

2 posts - 2 participants

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Buffered Streams

I’ve been working on an application using GNAT.Sockets with calls to Receive_Socket and Send_Socket. I’ve been hesitant to use the Stream interface because I want writes coalesced into reasonably large (~64k) buffers for performance reasons.

I have my own buffered stream implemention right now, but I’m wondering if others have better solutions.

6 posts - 4 participants

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Bug in GNAT Get(FRom => SomeString, Item => SomeInteger, Last => Last)?

Get(TheFile, IntValue); works great with strings formatted like 16#12# to read hex values. Shouldn't Get from a string function the same way?

I tried this, but passing 16#12# only yields 16. Pure hex, eg F8 results in an exception

with Ada.Text_IO;         use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;

procedure hex is
   IntValue  : Integer;
   Last : Positive;
begin
   Put("Enter a hexadecimal string: ");
   Get(HexString);

   -- Convert the hexadecimal string to an integer
   Get(From => HexString, Item => IntValue, Last => Last);

   Put ("The integer value is: ");
   Put (IntValue, Width => 0);
   New_Line;
end hex;

Recursion – implementing sum

There are lots of easy to understand recursive algorithms. One of the easiest is is a function sum(x) which sums up all the integers from 1 to x. Here is the function implemented in Ada.

function sum(n: integer) return integer is
begin
   if n = 1 then 
      return 1;
   else 
      return (n + sum(n-1));
   end if;
end sum;

Here the function sum(x) recurses until the value of x becomes 0. At this point the recursion is essentially done, and the calls to sum() backtrack. This is shown in the summary below for sum(5).

sum(5) = (5 + sum(4))                          recursive call sum(4)
       = (5 + (4 + sum(3)))                    recursive call sum(3)
       = (5 + (4 + (3 + sum(2))))              recursive call sum(2)
       = (5 + (4 + (3 + (2 + sum(1)))))        recursive call sum(1), return 1
       = (5 + (4 + (3 + (2 + 1))))             return (2 + 1)
       = (5 + (4 + (3 + 3)))                   return (3 + 3)
       = (5 + (4 + 6))                         return (4 + 6)
       = (5 + 10)                              return (5 + 10)
       = 15

There are four recursive calls to sum() in addition to the original call, which is not considered recursive, because the function may actually terminate, e.g. if sum(1) is invoked. So if the function were to call sum(10000), there would be 9,999 recursive calls. The problem with recursion of course is that many of these simplistic algorithms are just as easy to implement as iterative algorithms.

Here is the same algorithm represented iteratively:

function sumi(n: integer) return integer is
   s : integer;
begin
   s := 0;
   for i in 1..n loop
      s := s + i;
   end loop;
   return s;
end sumi;

How to pass complex data types, like records between Ada and C via a DLL?

I am trying to get Ada code to compile to a DLL to be callable in C. So far I have managed to get this to work for simple types such as integers but i'm having difficulty with more complex types such as array's or records/structs.

Below is my Ada code for an record/struct. It is a dynamic library which i compile to a dll using the command "gprbuild -P ./math.gpr -p":

person.adb
with Interfaces.C; use Interfaces.C;

package body Person is

   function Set_Age_To_Five(P : Person_Record) return Person_Record is
      Result : Person_Record;
   begin
      Result := P;
      Result.Age := 5;
      return Result;
   end Set_Age_To_Five;

end Person;

person.ads

with Interfaces.C; use Interfaces.C;

package Person is

   type Person_Record is record
      Name    : String(1 .. 100);
      Age     : Interfaces.C.int;
      Address : String(1 .. 100);
   end record with Convention => C_Pass_By_Copy;

   function Set_Age_To_Five(P : Person_Record) return Person_Record;
   pragma Export (C, Set_Age_To_Five, "Set_Age_To_Five");

end Person;

math.gpr

library project Math is
    for Languages use ("Ada");
    for Library_Name use "Person";
    for Source_Dirs use ("src");
    for Object_Dir use "obj";
    for Library_Dir use "lib";
    for Library_Kind use "Dynamic";
end Math;

I then have a C header file math.h:

#ifndef MATH_H
#define MATH_H

#ifdef __cplusplus
extern "C"
#endif

typedef struct {
    char Name[101];
    int Age;
    char Address[101];
} Person_Record;

Person_Record Set_Age_To_Five(Person_Record P);

#ifdef __cplusplus

#endif

#endif /* MATH_H */

and finally my C code:

#include <stdio.h>
#include "math.h"

int main() {
    Person_Record p, q, r;

    // Initialize the person record
    snprintf(p.Name, sizeof(p.Name), "John");
    p.Age = 25;
    snprintf(p.Address, sizeof(p.Address), "123 Main St");

    // Call the Set_Age_To_Five function from the DLL
    q = Set_Age_To_Five(p);

    // Print the modified person record
    printf("Name: %s\n", q.Name);
    printf("Age: %d\n", q.Age);
    printf("Address: %s\n", q.Address);

    return 0;
}

This should when executed return

Name: John
Age: 5
Address: 123 Main St

Instead its returning:

Name: John
Age: 25
Address: 123 Main St

I've tried passing by variable, passing by reference. using convention C and convention pass by c in ada.

New project: Alice

After months of dedicated work, I'm thrilled to introduce my project: Alice!

Alice, Adventures for Learning and Inspiring Coding Excellence, is a collaborative Ada framework that allows programmers to enhance and share their solutions to various problem sources (e.g. Project Euler, CodinGame and Advent of Code), fostering collaboration, learning and creativity.

While it's currently in the proof of concept stage, and only Project Euler is supported, I believe it holds immense potential.

The wiki pages offer a glimpse into Alice's concept, participation opportunities, and development ideas.

I warmly invite all members of the Ada community, as well as beginners and students exploring Ada, to read across the wiki pages and share your valuable feedback. Your insights and input will be instrumental in shaping Alice's future. Together, let's unlock the possibilities and make a significant impact.

Stay tuned for the upcoming public release, as we embark on this exciting journey together!

submitted by /u/f-rocher
[link] [comments]

New project: Alice

After months of dedicated work, I’m thrilled to introduce my project: Alice!

Alice, Adventures for Learning and Inspiring Coding Excellence, is a collaborative Ada framework that allows programmers to enhance and share their solutions to various problem sources (e.g. Project Euler, CodinGame and Advent of Code), fostering collaboration, learning and creativity.

While it’s currently in the proof of concept stage, and only Project Euler is supported, I believe it holds immense potential.

The Alice wiki pages offer a glimpse into Alice’s concept, participation opportunities, and development ideas.

I warmly invite all members of the Ada community, as well as beginners and students exploring Ada, to read across the wiki pages and share your valuable feedback. Your insights and input will be instrumental in shaping Alice’s future. Together, let’s unlock the possibilities and make a significant impact.

Stay tuned for the upcoming public release, as we embark on this exciting journey together!

3 posts - 2 participants

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[ANN] Ayacc 1.4 and Aflex 1.6

I’ve made new versions for Ayacc and Aflex with several improvements. To summarize:

  • support for reentrant scanner and parser,
  • Bison like options to tune the generated parser,
  • some code block injection (à la Bison) to customize the scanner and parser…

You can use them with Alire as follows:

alr get aflex
cd aflex_1.6.0_b3c21d99
alr build
alr install
alr get ayacc
cd ayacc_1.4.0_c06f997f
alr build
alr install

For a more detailed explanation about the reentrant support, have a look at Reentrant scanner and parser with Aflex and Ayacc

9 posts - 3 participants

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Reentrant scanner and parser with Aflex and Ayacc

[Aflex and Ayacc](Ada/Aflex-Ayacc-code.jpg)
    1. What's new in Aflex 1.6

- Support the flex options `%option output`, `%option nooutput`, `%option yywrap`, `%option noinput`,

 `%option noyywrap`, `%option unput`, `%option nounput`, `%option bufsize=NNN` to better control the
 generated `_IO` package.
- Aflex(https://github.com/Ada-France/aflex) templates provide more control for tuning the code generation and
 they are embedded with [Advanced Resource Embedder](https://gitlab.com/stcarrez/resource-embedder)
- Support to define Ada code block in the scanner that is inserted in the generated scanner - New option -P to generate a private Ada package for DFA and IO - New directive `%option reentrant` and `%yyvar` to generate a recursive scanner - New directive `%yydecl` to allow passing parameters to `YYLex`
 or change the default function name

Example of `%option` directives to tell Aflex(https://github.com/Ada-France/aflex) to avoid generating several function or procedures and customize the buffer size.

```Ada %option nounput %option noinput %option nooutput %option noyywrap %option bufsize=1024 ```

The tool supports some code block injection at various places in the generated scanner. The code block has the following syntax where `<block-name>` is the name of the code block:

```Ada %<block-name> {

 -- Put Ada code here

} ```

The `%yytype` code block can contain type declaration, function and procedure declarations. It is injected within the `YYLex` function in the declaration part. The `%yyinit` code block can contain statements that are executed at beginning of the `YYLex` function. The `%yyaction` code block can contain statements that are executed before running any action. The `%yywrap` code block can contain statements which are executed when the end of current file is reached to start parsing a next input.

    1. What's new in Ayacc 1.4

- Support the Bison `%define variable value` option to configure the parser generator - Support the Bison `%code name { ... }` directive to insert code verbatim into the output parser - Recognize some Bison variables `api.pure`, `api.private`, `parse.error`, `parse.stacksize`,

 `parse.name`, `parse.params`, `parse.yyclearin`, `parse.yyerrok`, `parse.error`
- New option `-S skeleton` to allow using an external skeleton file for the parser generator - Ayacc(https://github.com/Ada-France/ayacc) templates provide more control for tuning the code generation and
 they are embedded with [Advanced Resource Embedder](https://gitlab.com/stcarrez/resource-embedder)
- New option `-P` to generate a private Ada package for the tokens package - Improvement to allow passing parameters to `YYParse` for the grammar rules - New `%lex` directive to control the call of `YYLex` function - Fix #6: ayacc gets stuck creating an infinitely large file after encountering a comment in an action

The generator supports two code block injections, the first one `decl` is injected in the `YYParse` procedure declaration and the `init` is injected as first statements to be executed only once when the procedure is called. The syntax is borrowed from the Bison parser:

```Ada %code decl {

  -- Put Ada declarations

} %code init {

  -- Put Ada statements

} ```

Some other Bison like improvements have been introduced to control the generation of the parser code.

``` %define parse.error true %define parse.stacksize 256 %define parse.yyclearin false %define parse.yyerrok false %define parse.name MyParser ```

    1. How to use

The easiest way to use Ayacc(https://github.com/Ada-France/ayacc) and Aflex(https://github.com/Ada-France/aflex) is to use Alire(https://github.com/alire-project/alire), get the sources, build them and install them. You can do this as follows:

``` alr get aflex cd aflex_1.6.0_b3c21d99 alr build alr install alr get ayacc cd ayacc_1.4.0_c06f997f alr build alr install ```

  • UPDATE*: the `alr install` command is available only with Alire(https://github.com/alire-project/alire) 2.0.

Using these tools is done in two steps:

1. a first step to call `aflex` or `ayacc` command with the scanner file or grammar file, 2. a second step to call `gnatchop` to split the generated file in separate Ada files

For example, with a `calc_lex.l` scanner file, you would use:

``` aflex calc_lex.l gnatchop -w calc_lex.ada ```

And with a `calc.y` grammar file:

``` ayacc calc.y gnatchop -w calc.ada ```

To know more about how to write a scanner file or grammar file, have a look at Aflex 1.5 and Ayacc 1.3.0(https://blog.vacs.fr/vacs/blogs/post.html?post=2021/12/18/Aflex-1.5-and-Ayacc-1.3.0) which explains more into details some of these aspects.

    1. Highlight on reentrancy

By default Aflex(https://github.com/Ada-France/aflex) and Ayacc(https://github.com/Ada-France/ayacc) generate a scanner and a parser which use global variables declared in a generated Ada package. These global variables contain some state about the scanner such as the current file being scanned. The Ayacc(https://github.com/Ada-France/ayacc) parser generates on its side two global variables `YYLVal` and `YYVal`.

Using global variables creates some strong restrictions when using the generated scanner and parser: we can scan and parse only one file at a time. It cannot be used in a multi-thread environment unless the scan and parse is protected from concurrent access. We cannot use easily some grammars that need to recurse and parse another file such as an included file.

      1. Reentrant scanner

The reentrant scanner is created by using the `-R` option or the `%option reentrant` directive. The scanner will then need a specific declaration with a context parameter that will hold the scanner state and variables. The context parameter has its type generated in the `Lexer_IO` package. The `%yydecl` directive in the scanner file must be used to declare the `YYLex` function with its parameters. By default the name of the context variable is `Context` but you can decide to customize and change it to another name by using the `%yyvar` directive.

``` %option reentrant %yyvar Context %yydecl function YYLex (Context : in out Lexer_IO.Context_Type) return Token ```

When the `reentrant` option is activated, Aflex(https://github.com/Ada-France/aflex) will generate a first `Context_Type` limited type in the `Lexer_DFA` package and another one in the `Lexer_IO` package. The generator can probably be improved in the future to provide a single package with a single type declaration. The `Lexer_DFA` package contains the internal data structures for the scanner to maintain its state and the `Lexer_IO` package holds the input file as well as the `YYLVal` and `YYVal` values.

      1. Reentrant parser

On its side, Ayacc(https://github.com/Ada-France/ayacc) uses the `YYLVal` and `YYVal` variables. By default, it generates them in the `_tokens` package that contains the list of parser symbols. It must not generate them and it must now use the scanner `Context_Type` to hold them as well as the scanner internal state. The setup requires several steps:

1. The reentrant parser is activated by using the `%define api.pure`

  directive similar to the [bison %define](https://www.gnu.org/software/bison/manual/html_node/_0025define-Summary.html).

2. The `%lex` directive must be used to define how the `YYLex` function must be called since it now has some

  context parameter.

3. The scanner context variable must be declared somewhere, either as parameter to the `YYParse`

  procedure or as a local variable to `YYParse`.  This is done using the new `%code decl` directive
  and allows to customize the local declaration part of the `YYParse` generated procedure.

4. We must give visibility of the `YYLVal` and `YYVal` values defined in the scanner context variable.

  Again, we can do this within the `%code decl` directive.

A simple reentrant parser could be defined by using:

```Ada %define api.pure true %lex YYLex (Scanner) %code decl {

     Scanner : Lexer_IO.Context_Type;
     YYLVal  : YYSType renames Scanner.YYLVal;
     YYVal   : YYSType renames Scanner.YYVal;

} ```

However, this simple form is not really useful as you may need to open the file and setup the scanner to read from it. It is probably better to pass the scanner context as parameter to the `YYParse` procedure. For this, we can use the `%define parse.params` directive to control the procedure parameters. The reentrant parser is declared as follows:

```Ada %lex YYLex (Scanner) %define api.pure true %define parse.params "Scanner : in out Lexer_IO.Context_Type" %code decl {

     YYLVal : YYSType renames Scanner.YYLVal;
     YYVal  : YYSType renames Scanner.YYVal;

} ```

To use the reentrant parser and scanner, we only need to declare the scanner context, open the file by using the `Lexer_IO.Open_Input` procedure and call the `YYParse` procedure as follows:

```Ada

 Scanner : Lexer_IO.Context_Type;
 ...
   Lexer_IO.Open_Input (Scanner, "file-to-scan");
   YYParse (Scanner);

```

      1. Grammar examples:

To have a more complete example of a reentrant parser, you may have a look at the following files:

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