[PATCH] ash: support platforms that don't have '%m' printf specifier

[Jody Bruchon]

On 2017-07-27 12:16, Xabier Oneca -- xOneca wrote:
> Hello:
>
> 2017-07-27 17:48 GMT+02:00 Ron Yorston <rmy at pobox.com>:
>> Kang-Che Sung wrote:
>>> dietlibc supports %m only if WANT_ERROR_PRINTF is defined in
>>> <dietfeartures.h> when building, and its commented out by default.
>>> I don't know how to check the macro WANT_ERROR_PRINTF in
>>> the dietlibc build environment, but I think busybox needs to be
>>> aware of this.
>> There doesn't seem to be anything in a standard build of dietlibc
>> to allow detection of this at (application) build-time.  The
>> dietfeatures.h include file is only available when the library is
>> built; it isn't installed.
>>
>> I suppose if the default is for '%m' to be disabled that's what
>> BusyBox should assume.  If someone has built dietlibc with the
>> non-default option they should be capable of doing the same for
>> BusyBox.
>>
>> Unless any dietlibc users have a better suggestion...
>>
>> Ron
> Try to compile a little application that uses this functionality and
> check for success, as would be done with autoconf. Not suggesting to
> do that, just giving ideas...
>
> Cheers,
>
> Xabier Oneca_,,_
IMO the whole issue is that %m is non-standard despite having moderate 
de facto acceptance in many libc implementations. I think BusyBox should 
comply with the standards instead of having a compile-time hack and 
added code complication to save a couple of bytes by switching to %m. 
There is no guarantee that a particular BusyBox binary built to use a 
library with %m won't be moved from that machine to one with the same 
libc but without %m built in (I don't know if dietlibc could bring such 
a situation to reality but it wouldn't surprise me.) As far as I can see 
the only savings by using %m would be one parameter off of a [f]printf() 
and one function call to strerror() removed; how much is that really 
saving, and is it worth the added code complexity and the non-compliance 
with the standards?

-Jody