##### 23.3.3.16 Accessing blocks from Guile.

In gdb, symbols are stored in blocks. A block corresponds roughly to a scope in the source code. Blocks are organized hierarchically, and are represented individually in Guile as an object of type `<gdb:block>`. Blocks rely on debugging information being available.

A frame has a block. Please see Frames In Guile, for a more in-depth discussion of frames.

The outermost block is known as the global block. The global block typically holds public global variables and functions.

The block nested just inside the global block is the static block. The static block typically holds file-scoped variables and functions.

gdb provides a method to get a block's superblock, but there is currently no way to examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (see Symbol Tables In Guile).

Here is a short example that should help explain blocks:

         /* This is in the global block.  */
         int global;

         /* This is in the static block.  */
         static int file_scope;

         /* 'function' is in the global block, and 'argument' is
            in a block nested inside of 'function'.  */
         int function (int argument)
         {
           /* 'local' is in a block inside 'function'.  It may or may
              not be in the same block as 'argument'.  */
           int local;

           {
              /* 'inner' is in a block whose superblock is the one holding
                 'local'.  */
              int inner;

              /* If this call is expanded by the compiler, you may see
                 a nested block here whose function is 'inline_function'
                 and whose superblock is the one holding 'inner'.  */
              inline_function ();
           }
         }

The following block-related procedures are provided by the `(gdb)` module:

— Scheme Procedure: block? object

> Return `#t` if object is a `<gdb:block>` object. Otherwise return `#f`.

— Scheme Procedure: block-valid? block

> Returns `#t` if `<gdb:block>` block is valid, `#f` if not. A block object can become invalid if the block it refers to doesn't exist anymore in the inferior. All other `<gdb:block>` methods will throw an exception if it is invalid at the time the procedure is called. The block's validity is also checked during iteration over symbols of the block.

— Scheme Procedure: block-start block

> Return the start address of `<gdb:block>` block.

— Scheme Procedure: block-end block

> Return the end address of `<gdb:block>` block.

— Scheme Procedure: block-function block

> Return the name of `<gdb:block>` block represented as a `<gdb:symbol>` object. If the block is not named, then `#f` is returned.

> For ordinary function blocks, the superblock is the static block. However, you should note that it is possible for a function block to have a superblock that is not the static block – for instance this happens for an inlined function.

— Scheme Procedure: block-superblock block

> Return the block containing `<gdb:block>` block. If the parent block does not exist, then `#f` is returned.

— Scheme Procedure: block-global-block block

> Return the global block associated with `<gdb:block>` block.

— Scheme Procedure: block-static-block block

> Return the static block associated with `<gdb:block>` block.

— Scheme Procedure: block-global? block

> Return `#t` if `<gdb:block>` block is a global block. Otherwise return `#f`.

— Scheme Procedure: block-static? block

> Return `#t` if `<gdb:block>` block is a static block. Otherwise return `#f`.

— Scheme Procedure: block-symbols

> Return a list of all symbols (as <gdb:symbol> objects) in `<gdb:block>` block.

— Scheme Procedure: make-block-symbols-iterator block

> Return an object of type `<gdb:iterator>` that will iterate over all symbols of the block. Guile programs should not assume that a specific block object will always contain a given symbol, since changes in gdb features and infrastructure may cause symbols move across blocks in a symbol table. See Iterators In Guile.

— Scheme Procedure: block-symbols-progress?

> Return #t if the object is a <gdb:block-symbols-progress> object. This object would be obtained from the `progress` element of the `<gdb:iterator>` object returned by `make-block-symbols-iterator`.

— Scheme Procedure: lookup-block pc

> Return the innermost `<gdb:block>` containing the given pc value. If the block cannot be found for the pc value specified, the function will return `#f`.