Re: libelf gelf_newehdr and gelf_newphdr return types

[Ali Bahrami <Ali dot Bahrami at Oracle dot COM>]

On 12/ 2/16 12:00 PM, Josh Stone wrote:
> I'd favor uintptr_t to keep better compatibility with current elfutils.
>
> That's not perfect either, since glibc uses "unsigned int" on 32-bit
> platforms, so that could still cause warnings for things that strictly
> expect long, like printf "%lx".  But directly printing a newehdr return
> value (without saving it somewhere) is a weird thing to do, so I think
> we can dismiss that case, at least.  Off the top of my head, I can't
> think of anything else that's so strict about long vs. int.
>
> Another option is to make the change conditional on __LP64__, so
> existing platforms are totally unaffected.  I'd still lean toward
> uintptr_t for the new case, so existing libelf code can port easily.


    In a 32-bit environment, int, long, and (void *) are all a 32-bit
integer at the machine level. That's true for any unix I know about
(including Linux) and also for Win32 and Win64 (and I presume that
no one cares about Win16). As a result, printf "%x" and "%lx"
are equivalent. The compiler might warn, but the code it generates
would be correct, and so, the noise is a good thing --- it will
encourage you to go change your printf to use "%p", but if you
ignore it, nothing bad will occur as a result.

I expect very little compiler noise for C programs, because in C,
'void *' is very promiscuous, and adapts without complaint to any
assignment. C++ might be a bigger issue, and I guess the question there
is: How much C++ code is out there using these, and why would it not be
better for that code to just get fixed? Even in C++, existing old C++
binaries would continue to run without issue.

Although uintptr_t would work, it seems unnecessary. Note that freebsd
already uses 'void *', and surely they build most of the same ELF-related
FOSS code that we might be concerned about, so I think that the libelf
code already has ported easily. As such, and given that 'void *' is the
common C idiom for this sort of use, I think it would make sense to
use it.

We should all do the experiment and report back.

- Ali