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Re: RFA: Do solib address arithmetic with appropriate truncation
> 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