Re: dwarf2-frame.c question for maintainers

[Andrew Cagney <cagney@gnu.org>]

> On Wed, 2004-07-14 at 12:28, Andrew Cagney wrote:
> 
>>>>>> >>> How come extract_typed_address, in read_reg, doesn't sign extend?
>>>
>>>> > 
>>>> > 
>>>> > I should have explained that. It does.  However extract_typed_address is
>>>> > incorrect because it makes the invalid assumption that sizeof(address)
>>>> > == sizeof(register).  So that has to go and be replaced with something
>>>> > like
>>>> > extract_signed_integer (buf, register_size (current_gdbarch, regnum));
>>
>>> 
>>> You mean the builtin_type_void_data_ptr parameter to 
>>> extract_typed_address?  Ah.
>>> 
>>> I see builtin_type_void_data_ptr dates back to 1.1 (Mark?).  It could 
>>> instead use the register's type?
> 
> 
> extract_typed_address calls extract_[un]signed_integer with size =
> TYPE_LENGTH of builtin_type_void_data_ptr.
> 
> Here's exactly what I am seeing.  Maybe you can tell me if read_reg is
> the problem.
> 
> For example big-endian Mips, with o64 or (eabi and mlong32):
> (registers are 64 bits and pointers are 32 bits)
> 
> read_reg calls frame_unwind_register (next_frame, regnum, buf)
> after that, buf has something like ffffffff801fffb8
> 
> Now if you do extract_typed_address(), it knows addresses are 4 bytes
> and returns 0xffffffff sign extended to 0xfffffffffffffff

Right, as it stands, that call is just wrong.

> If instead, you call extract_[un]signed_integer((buf, register_size
> (current_gdbarch, regnum)), it returns 0xffffffff801fffb8
> 
> The real problem here is the the size.  AFAICT, sign-extension here is
> unimportant; I get the same test results calling 
> extract_unsigned_integer in read_reg() for mips, because, as you can
> see, nothing needs extending, just the whole register needs read.
> However, I can't prove that is always the case because I am not familiar
> enough with the code.

Consider o32.  Both the ABI and ISA are 32-bits, but GDB's CORE_ADDR may 
be 64-bits.  Even if it doesn't appear to make a difference, the MIPS 
needs to always sign extend addresses/registers - that's the dogma :-)

Andrew