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RFC: Adding an extra field to Elf_Internal_Sym

H.J. Lu hjl.tools@gmail.com
Tue Nov 30 21:45:00 GMT 2010 
On Tue, Nov 30, 2010 at 9:40 AM, Richard Sandiford
<richard.sandiford@linaro.org> wrote:
> Richard Earnshaw <rearnsha@arm.com> writes:
>> On Tue, 2010-11-30 at 17:00 +0000, Richard Sandiford wrote:
>>> Richard Earnshaw <rearnsha@arm.com> writes:
>>> > I think your argument about the risk of externally exposing internal
>>> > data is persuasive.  Other than that, I have no objection to either
>>> > approach provided it doesn't change anything in the written object file.
>>>
>>> OK, thanks.
>>>
>>> > I think there's perhaps also an argument for doing something along these
>>> > lines for the T bit in function symbols.  At present the use of
>>> > STT_THUMB_FUNC internally causes tools like nm to incorrectly list Thumb
>>> > function symbols.
>>>
>>> Do you mean keeping the T bit in the symbol value, rather than masking
>>> it out?
>>>
>>> I'd originally rejected that because it seemed to make things more
>>> complicated.  I hadn't realised "nm" got things wrong though.  If we do
>>> want things like "nm" to print the in-object symbol value, then maybe we
>>> should go that way and add helper functions to mask out the T bit when
>>> needed.
>>
>> No, I was thinking of moving it to a different field (attribute) rather
>> than changing the type of the symbol (so all function symbols are then
>> STT_FUNC).
>>
>> There certainly is an argument that nm should use the raw value field of
>> a symbol, but I'm more concerned at present that we get output such as
>>
>> sym                 |00000000|   T  |<processor specific>: 13|        |     |.text
>>
>> Which is misleading on ARM EABI as there is no such type...
>
> Ah, yeah, hadn't thought of trying sysv mode.  That does seem a
> convincing argument against making up a new internal-only symbol type
> for Thumb STT_GNU_IFUNCs.  It looks like it is a choice between the new
> Elf_Interanl_Sym field (which fixes the output above) and keeping the T
> bit in the raw symbol value.
>
> Does anyone have any feel for how disruptive it would be for users
> if we make nm print odd values?

I have found nm pretty much useless on some ELF symbols.  For
example, nm doesn't report value for ELF COMMON symbols.


-- 
H.J.
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