Re: RFA: Do solib address arithmetic with appropriate truncation

[Andrew Cagney <ac131313 at cygnus dot com>]

> Andrew Cagney <ac131313@cygnus.com> writes:
> 
>> > There must be something around that this code can use.  On something
> 
>> >> like a mips, this would be wrong - remember the sign extension problem.
> 
>> > I've never really understood the MIPS sign extension problem.  Does
>> > it
>> > occur when TARGET_PTR_BIT is smaller than the size of one or more of
>> > the registers used to hold addresses?
> 
>> 
>> 
>> The MIPS ISA when running 32 bit code, sign extends pointers.  GDB
>> mimics this behavour.  If it encounters a 32 bit pointer it will
>> convert it to/from a cannonical form (sign extended CORE_ADDR for
>> MIPS).   Such pointers occure everywhere - debug info, registers,
>> memory, ... By always sign extending, GDB avoids any potential
>> inconsistency and latent bugs.  POINTER_TO_ADDRESS and
>> ADDRESS_TO_POINTER handle this.
>> 
>> When debugging MIPS, the first thing to check is that CORE_ADDRs are
>> sign exteded.  A value like ``0x80001234'' as the patch would
>> generate, indicate a bug.
>> 
>> Interestingly, the SPARC is showing signs of the same, or similar, problems.
> 
> 
> Let me get this straight.  From reading the .so file's section header
> table, I'm going to get 64-bit offsets, right?  And from reading the
> dynamic linker's table of loaded shared libraries, I'm going to get
> 32-bit offsets, right?


A 32 or 64 bit section header?


> So, if I have a .so section which says its offset is 0xf0000000, and
> the dynamic linker's table says that the .so has been loaded at an
> offset of 0x20000000, should I determine that the address at which the
> section was actually loaded is 0x110000000, or 0x10000000?


Assuming 64 bit section header and 32 bit offset (TARGET_PTR_BIT == 64).

0xf0000000 -> 0xfffffffff0000000
0x20000000 -> 0x0000000020000000
--------------------------------
               0x0000000010000000

Assuming a 32 bit MIPS section header and offset (TARGET_PTR_BIT == 32 
and address<->pointer is signed):

0xf0000000
0x20000000
----------
0x10000000 -> 0x0000000010000000


> Or, if the section's offset is 0x70000000, and the dynamic linker says
> the .so is loaded at an offset of 0x20000000, do I get a section address
> of 0xffffffff90000000, or 0x0000000090000000?
> 
> Spell it out for me, baby.  :)


Assuming 64 bit section header and 32 bit offset:

0x70000000 -> 0x0000000070000000
0x20000000 -> 0x0000000020000000
--------------------------------
               0x0000000090000000

Assuming a 32 bit MIPS section header and offset:

0x70000000
0x20000000
----------
0x90000000 -> 0xffffffff90000000

Andrew