[v3,14/14] the "compile" command

  On Sun, 02 Nov 2014 17:02:48 +0100, Eli Zaretskii wrote:
> > +Compile @var{source} with the compiler language set as the current
> > +language in @value{GDBN} (@pxref{Languages}).
> 
> Does the user need to set the language, or will the language from the
> debug info be used, if available?

The latter.

> If the latter, the wording here needs to be modified, as it currently
> implies one needs to set the language "in GDB".

Used s/set/found/.
	Compile @var{source} with the compiler language found as the current
	language in @value{GDBN} (@pxref{Languages}).

> > If compilation and
> > +injection is not supported with the current language specified in
> > +@value{GDBN}, or the compiler does not support this feature,
> 
> Which "this feature" needs to be supported by the compiler?

The "compilation and injection" - the libcc1.so module and its
gcc_c_fe_context() interface for GDB.

> > +message will be printed.  If @var{source} compiles and links
> > +successfully, @value{GDBN} will load the object-code emitted,
> 
> Judging by the example, I would suggest to use @var{source-code}
> instead of @var{code}.

You wanted to say "instead of @var{source}.".

Changed it in these lines:
	@item compile code @var{source-code}
	@itemx compile code -raw @var{--} @var{source-code}
	Compile @var{source-code} with the compiler language found as the current
	[...]
	message will be printed.  If @var{source-code} compiles and links
	[...]
	provided @var{source-code} in a callable scope.  In this case, you must

> > +The command allows you to specify source code in two ways.  The simplest
> 
> @var{code}, so that the reader realizes you are talking about the
> argument mentioned above.

I think it should be @var{source-code} now, therefore used:
	The command allows you to specify @var{source-code} in two ways.  

> > +Specifying @samp{-raw}, prohibits @value{GDBN} from wrapping the
> > +provided @var{source} in a callable scope.  In this case, you must
> > +specify the entry point of the code by defining a function named
> > +@code{_gdb_expr_}.  The @samp{-raw} code does not automatically
> > +access variables of the inferior, for their import you must use the
> > +@samp{#pragma} line first:
> > +
> > +@smallexample
> > +#pragma GCC user_expression
> > +@end smallexample
> 
> I think an example of using 'raw' is in order; the description above
> is not very clear.
> 
> > +@samp{#include} lines are better to be placed before the @samp{#pragma}
> > +line.
> 
> Why? what happens if one doesn't?

While debugging it I have found that for -raw file #pragma GCC user_expression
does not make sense as it does not work - it is explicitly disabled by:
gdb/compile/compile-c-symbols.c
       /* Don't emit local variable decls for a raw expression.  */
       if (context->base.scope != COMPILE_I_RAW_SCOPE
          || symbol_name == NULL)

Therefore I have reworked the paragraph to:
	Specifying @samp{-raw}, prohibits @value{GDBN} from wrapping the
	provided @var{source-code} in a callable scope.  In this case, you must
	specify the entry point of the code by defining a function named
	@code{_gdb_expr_}.  The @samp{-raw} code cannot access variables of the
	inferior.  Using @samp{-raw} option may be needed for example when
	@var{source-code} requires @samp{#include} lines which may conflict with
	inferior symbols otherwise.

In the future we may extend -raw to make the inferior variables accessible
somehow but as that requires GDB-generated code it mostly conflicts with the
goal of -raw.

> >        The use of @samp{-raw} is considered to be expert usage, and care
> > +should be taken when using it.
> 
> Like what?
> 
> This kind of remarks in documentation are "considered harmful": either
> explain in detail what you mean, or don't say that at all.  Leaving
> mysterious comments about "here be dragons" doesn't help the reader
> understand how to use the feature correctly.

Removed it.

> > +If the filename/path contains whitespace it must be enclosed in
> > +quotes.
> 
> Which quotes? single? double?

I have found if the filename/path contains whitespace it must be left as is,
without any quotes of any kind.  I have removed the sentence; or do you
suggested something else?

> > +There are a few caveats to keep in mind when using the @code{compile}
> > +command.  As the caveats are different per language, the table below
> > +highlights specific issues on a per language basis.
> 
> This and the following stuff is better put in its own subsection.

Done:
	@subsection Caveats when using the @code{compile} command

> > +something else in the example program changes it, or another
> > +@code{compile} command changes it.
> 
> So why did you say the changes are persistent?  Persistent might mean
> the value will be the same if the program is re-run.

The command "compile code k = 3;" makes the change persistent.  Contrary to it
command "compile code int k = 3;" would not be persistent which is described
about 3 paragraphs beneath:
	Variables and types that are created as part
	of the @code{compile} command are not persistent, and only exist as
	long as the injected object code exists.  This example is valid:

	@smallexample
	compile code int ff = 5; printf ("ff is %d\n", ff);
	@end smallexample

> > +Normal scope and access rules apply to source code compiled and injected
> > +by the @code{compile} command.  In the example, the variables @code{j}
> > +and @code{k} are not accessible; subsequent execution will bring these
> > +variables into scope, and later, code written and compiled with the
> > +@code{compile} command will be able to access them.  At this point the
> > +program is stopped in the @code{main} function so the following example:
> > +
> > +@smallexample
> > +compile code j = 3;
> > +@end smallexample
> > +
> > +would result in a compilation error, and @value{GDBN} would print that
> > +error to the console.
> 
> I needed to read this twice to understand what you mean.  Suggest to
> reword as follows:
> 
>   Normal scope and access rules apply to source code compiled and
>   injected by the @code{compile} command.  In the example, the variables
>   @code{j} and @code{k} are not accessible yet, because the program is
>   currently stopped in the @code{main} function, where these variables
>   are not in scope.  Therefore, the following command
> 
>   @smallexample
>   compile code j = 3;
>   @end smallexample
> 
>   @noindent
>   will result in a compilation error message.
> 
>   Once the program is continued, execution will bring these variables in
>   scope, and they will become accessible; then the code you specify via
>   the @code{compile} command will be able to access them.

I do not see there a difference but I used your text.

> > +However, if you were to type the following into @value{GDBN} after that
> > +command has completed:
> > +
> > +@smallexample
> > +compile code printf ("ff is %d\n'', ff);
> > +@end smallexample
> > +
> > +A compiler error would be raised as the variable @code{ff} no longer
> 
> Again, @noindend after the @example, and start "a compiler error" with
> a lower-case letter, as this is a continuation of the sentence before
> the example.

TBH I do not agree with this formatting as the previous sentence has been
terminated by its colon (':').  I see the difference as:
	See the expression: 1+2=3  Now we have to start a new sentence.
	See the expression 1+2=3 while here we continue the sentence.
But sure following your directions.

> > +@code{k} does not require the existence of @code{ff} to maintain the value
> > +it has been assigned.  Pointers and other types of references require
> 
> "However, pointers ..."
> 
> What "other types"?  How about one or two examples?

I would say just "pointers" myself.  "references" would be possible in C++ but
currently this patchset supports only plain C.  Currently one can pass also
a function name but that gets converted to a function pointer.  Reference to
a nest function via trampoline would be in fact also a function pointer.

I have removed "and other types of references" for now.

> > +location when the command exists.  A general rule should be followed
> > +in that you should either assign @code{NULL} to any assigned pointers,
> > +or restore a valid location to the pointer before the command exits.
> 
> Why NULL?  Any constant address will do, right?

NULL is the only valid constant address.  Otherwise a valid address points to
some object.

I find that sentence correct.

> > +Similar caution must be exercised with any types defined in
> > +@code{compile} command.
> 
> I would explain what you mean by "defined types" here.  I'm guessing
> you mean structs, unions, and typedefs, but let's say this explicitly.

Therefore used:
	Similar caution must be exercised with any structs, unions, and typedefs 
	defined in @code{compile} command.

> >                             Types defined in the @code{compile} are also
> > +deleted when the command exits.
> 
> I think types are not deleted, they simply don't exist in compiled
> code.  Right?

The meaning is that for example in a second "compile" command the types
defined in previous "compile" command are no longer available.

> >                                    Therefore, if you cast a variable to a
> > +type defined in the @code{compile} command, care must be taken to ensure
> > +that any future need to resolve the type can be achieved.
> 
> I don't understand the meaning of this.  Defining a type and casting
> to a type are two different things, so what does this text warn about?

I have put there:
	@smallexample
	(gdb) compile code static struct a { int a; } v = { 42 }; argv = &v;
	(gdb) compile code printf ("%d\n", ((struct a *) argv)->a);
	gdb command line:1:36: error: dereferencing pointer to incomplete type ‘struct a’
	Compilation failed.
	(gdb) compile code struct a { int a; }; printf ("%d\n", ((struct a *) argv)->a);
	42
	@end smallexample

Attaching only the new gdb.texinfo diff.

Thanks,
Jan
gdb/doc/ChangeLog
    2014-10-07  Phil Muldoon  <pmuldoon@redhat.com>
    	    Jan Kratochvil  <jan.kratochvil@redhat.com>

    	* gdb.texinfo (Altering): Update.
    	(Compiling and Injecting Code): New node.

[v3,14/14] the "compile" command

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