> >       /* Step 2: ldr Rd, [Rn, #immed], encoding T1.  */
> >       /* Step 3: str Rd, [Rn, #immed], encoding T1.  */
> >
> > Looking at the code and the function description, it seems to me
> > that the normal situation would be what the comment alluded to,
> > and that if it was the entire story, we wouldn't have needed
> > the code doing steps 2 & 3. But, looking at the email archives
> 
> Sorry, I don't understand why do you think steps 2 & 3 are not needed?
> Do you mean we don't have to go to step 2 & 3 if we can't find symbol
> __stack_chk_guard in step 1?

I see what you mean. I misread the code that it would stop if
the address was pointing to the __stack_chk_guard symbol. But
in reality, it stops if it is pointing to a symbol that is NOT
__stack_chk_guard.

> > as well as the bug report initially referenced, I can't find
> > really any explanation for what prompted you to add that code.
> > I would need that in order to adjust the heuristics without
> > breaking your situation.
> 
> Currently, we do so in order to handle the case symbol __stack_chk_guard
> is removed, as the comments said:
> 
>   /* If name of symbol doesn't start with '__stack_chk_guard', this
>      instruction sequence is not for stack protector.  If symbol is
>      removed, we conservatively think this sequence is for stack
>      protector.  */
> 
> However, I don't recall under what circumstance symbol
> '__stack_chk_guard' can be removed.  __stack_chk_guard is in .dynsym
> section, so it can't be removed.  (I presume symbols in .dynsym can't be
> removed, correct me if I am wrong).  If I am correct, we can restrict
> the condition in step 1 that return early if the symbol name doesn't
> start with '__stack_chk_guard'.  Then, step 2 & 3 is not needed, or we
> can keep them as a sanity check?

For heuristics, I would keep the heuristics as strict as possible
to avoid possible incorrect matches, so I would keep it.

What do you think of the attached patch?

gdb/ChangeLog:

        arm-tdep.c (arm_skip_stack_protector): Return early if
        address loaded by first "ldr" instruction does not have
        a corresponding minimal symbol.

Tested on arm-eabi using AdaCore's testsuite.

Thanks,
-- 
Joel