MI to access value of $ prefixed variable name

MI to access value of $ prefixed variable name

[Jonah Graham]

Hello,

I have a user of Eclipse CDT who is having problems displaying a C variable
called $j (dollar sign prefixed variable) -
https://bugs.eclipse.org/bugs/show_bug.cgi?id=573703

I understand this is because $ prefixed variables are treated specially by
GDB.

47-stack-list-locals --thread 1 --frame 0 1
47^done,locals=[{name="$f",value="0"}]

52-var-create --thread 1 --frame 0 - * $f
52^done,name="var3",numchild="0",value="void",type="void",has_more="0"

Note type "void" above, $f is an int in the C code, but is indeed void (as
expected) in GDB. -stack-list-locals shows the correct value, but I can't
use the returned name back to -var-create because of the naming conflict.

There wasn't anything I saw in the help (
https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Variable-Objects.html)
on this topic.

Thanks for your help.
Jonah

Re: MI to access value of $ prefixed variable name

[Simon Marchi]

On 2021-05-25 12:35 a.m., Jonah Graham wrote:
> Hello,
> 
> I have a user of Eclipse CDT who is having problems displaying a C variable
> called $j (dollar sign prefixed variable) -
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=573703
> 
> I understand this is because $ prefixed variables are treated specially by
> GDB.
> 
> 47-stack-list-locals --thread 1 --frame 0 1
> 47^done,locals=[{name="$f",value="0"}]
> 
> 52-var-create --thread 1 --frame 0 - * $f
> 52^done,name="var3",numchild="0",value="void",type="void",has_more="0"
> 
> Note type "void" above, $f is an int in the C code, but is indeed void (as
> expected) in GDB. -stack-list-locals shows the correct value, but I can't
> use the returned name back to -var-create because of the naming conflict.
> 
> There wasn't anything I saw in the help (
> https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Variable-Objects.html)
> on this topic.

Huh, I didn't know this was possible:

https://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar-Signs

I didn't look in depth, but I don't think there's a way to make it work.
I don't remember seeing a way to escape that dollar sign.

I'd say that the simplest solution would be: don't use dollar sign in
identifiers.  But if somebody really wants GDB to support it, then they
can always send a patch for it (I don't think this is a priority for
anyone).

Simon

Re: MI to access value of $ prefixed variable name

[Jonah Graham]

On Tue, 25 May 2021 at 10:04, Simon Marchi <simon.marchi@polymtl.ca> wrote:

> On 2021-05-25 12:35 a.m., Jonah Graham wrote:
> > Hello,
> >
> > I have a user of Eclipse CDT who is having problems displaying a C
> variable
> > called $j (dollar sign prefixed variable) -
> > https://bugs.eclipse.org/bugs/show_bug.cgi?id=573703
> >
> > I understand this is because $ prefixed variables are treated specially
> by
> > GDB.
> >
> > 47-stack-list-locals --thread 1 --frame 0 1
> > 47^done,locals=[{name="$f",value="0"}]
> >
> > 52-var-create --thread 1 --frame 0 - * $f
> > 52^done,name="var3",numchild="0",value="void",type="void",has_more="0"
> >
> > Note type "void" above, $f is an int in the C code, but is indeed void
> (as
> > expected) in GDB. -stack-list-locals shows the correct value, but I can't
> > use the returned name back to -var-create because of the naming conflict.
> >
> > There wasn't anything I saw in the help (
> >
> https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Variable-Objects.html
> )
> > on this topic.
>
> Huh, I didn't know this was possible:
>
> https://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar-Signs


The main place I have seen this in practice is generated code.


> I didn't look in depth, but I don't think there's a way to make it work.
> I don't remember seeing a way to escape that dollar sign.
>

No problem - thanks for the answer.

I'd say that the simplest solution would be: don't use dollar sign in
> identifiers.  But if somebody really wants GDB to support it, then they
> can always send a patch for it (I don't think this is a priority for
> anyone).
>

OK. I will update the bugzilla in CDT with this information.

Jonah

Re: MI to access value of $ prefixed variable name

[Tom Tromey]

>>>>> "Simon" == Simon Marchi via Gdb <gdb@sourceware.org> writes:

Simon> I'd say that the simplest solution would be: don't use dollar sign in
Simon> identifiers.  But if somebody really wants GDB to support it, then they
Simon> can always send a patch for it (I don't think this is a priority for
Simon> anyone).

I think it would be fine if someone wanted to solve this.
Maybe one idea would be to defer to variables from the inferior, but
provide some additional way to refer to convenience variables.  Or maybe
vice versa.

Tom