Re: Pb when calling a nested function in the inferior

Joel Brobecker
2001-07-31T00:24:00Z

> Have you verified that the mechanisms used by gcc and by Ada95 for
> passing the static chain are the same?

Yes. Actually, the code was exactly the same.

> 1) In the version of gcc that I'm using the symbol that's associated
> with get_value() is get_value.0. You could look for such symbols
> and refuse to allow them to be called as inferior functions.

this suggestion has my preference, being more general than the
suggestion below. Let me check it out.

> 2) You could scan the prologue and look for a sequence of instructions
> which looks like a save of the static chain. E.g, in your example,
> I see:
>
> 0x804842c <get_value.0>: push %ebp
> 0x804842d <get_value.0+1>: mov %esp,%ebp
> 0x804842f <get_value.0+3>: sub $0x4,%esp
> 0x8048432 <get_value.0+6>: mov %ecx,0xfffffffc(%ebp)
> 0x8048435 <get_value.0+9>: mov 0xfffffffc(%ebp),%ecx
> 0x8048438 <get_value.0+12>: mov %ecx,%ecx
> 0x804843a <get_value.0+14>: mov 0xfffffffc(%ecx),%eax
> 0x804843d <get_value.0+17>: mov %eax,%eax
> 0x804843f <get_value.0+19>: leave
> 0x8048440 <get_value.0+20>: ret
>
> It appears to me that ``mov %ecx,0xfffffffc(%ebp)'' is
> responsible for saving the static chain pointer. If you could
> detect this, you could print your error or warning. (You'd
> want to make sure that no other instruction with a destination
> of %ecx appears before this instruction in the prologue though;
> if it does, it means it's doing something else.)
>
> BTW, GDB isn't particularly graceful in its handling of the ``get_value.0''
> symbol. E.g, observe what happens when I do ``x/i get_value.0'':
>
> (gdb) x/i get_value.0
> No symbol "get_value" in current context.

That's curious. With my version of gdb, I don't get the same result
(using GNU gdb 2001-07-30-cvs (MI_OUT)):
(gdb) x/10i get_value.0
A parse error in expression, near `'.
(gdb) x/4i get_value
0x8048468 <get_value>: push %ebp
0x8048469 <get_value+1>: mov %esp,%ebp
0x804846b <get_value+3>: sub $0x4,%esp
0x804846e <get_value+6>: mov %ecx,0xfffffffc(%ebp)

--
Joel