[PATCH] tiny-printf: Support %i

Marek Vasut marex at denx.de
Tue Apr 14 17:22:19 CEST 2020

On 4/14/20 4:11 PM, Tom Rini wrote:
> On Tue, Apr 14, 2020 at 03:40:14PM +0200, Marek Vasut wrote:
>> On 4/14/20 3:26 PM, Tom Rini wrote:
>>> On Tue, Apr 14, 2020 at 02:24:18PM +0200, Marek Vasut wrote:
>>>> On 4/14/20 5:03 AM, Tom Rini wrote:
>>>>> On Tue, Apr 14, 2020 at 03:17:16AM +0200, Marek Vasut wrote:
>>>>>> On 4/14/20 1:27 AM, Tom Rini wrote:
>>>>>>> On Fri, Apr 10, 2020 at 08:54:49PM +0200, Marek Vasut wrote:
>>>>>>>> The most basic printf("%i", value) formating string was missing,
>>>>>>>> add it for the sake of convenience.
>>>>>>>> Signed-off-by: Marek Vasut <marex at denx.de>
>>>>>>>> Cc: Simon Glass <sjg at chromium.org>
>>>>>>>> Cc: Stefan Roese <sr at denx.de>
>>>>>>>> ---
>>>>>>>>  lib/tiny-printf.c | 3 ++-
>>>>>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>>>> diff --git a/lib/tiny-printf.c b/lib/tiny-printf.c
>>>>>>>> index 1138c7012a..8fc7e48d99 100644
>>>>>>>> --- a/lib/tiny-printf.c
>>>>>>>> +++ b/lib/tiny-printf.c
>>>>>>>> @@ -242,6 +242,7 @@ static int _vprintf(struct printf_info *info, const char *fmt, va_list va)
>>>>>>>>  				goto abort;
>>>>>>>>  			case 'u':
>>>>>>>>  			case 'd':
>>>>>>>> +			case 'i':
>>>>>>>>  				div = 1000000000;
>>>>>>>>  				if (islong) {
>>>>>>>>  					num = va_arg(va, unsigned long);
>>>>>>>> @@ -251,7 +252,7 @@ static int _vprintf(struct printf_info *info, const char *fmt, va_list va)
>>>>>>>>  					num = va_arg(va, unsigned int);
>>>>>>>>  				}
>>>>>>>> -				if (ch == 'd') {
>>>>>>>> +				if (ch != 'u') {
>>>>>>>>  					if (islong && (long)num < 0) {
>>>>>>>>  						num = -(long)num;
>>>>>>>>  						out(info, '-');
>>>>>>> How much does the size change and where do we see this as a problem?
>>>>>> Any code which uses %i in SPL just misbehaves, e.g.
>>>>>> printf("%s[%i] value=%x", __func__, __LINE__, val);
>>>>>> prints function name and then incorrect value, because %i is ignored.
>>>>>> This is also documented in the commit message.
>>>>>> U-Boot grows in size massively due to all the DM/DT bloat which is being
>>>>>> forced upon everyone, but there the uncontrolled growth is apparently OK
>>>>>> even if it brings no obvious improvement, rather the opposite. And yet
>>>>>> here, size increase suddenly matters? Sorry, that's not right.
>>>>>> The code grows by 6 bytes.
>>>>> Yes, it matters for _tiny-printf_ as that's where we have little to no
>>>>> room for growth.
>>>> How many systems that use tiny-printf in SPL are also forced to use DM
>>>> in SPL ?
>>> I don't know how many times I've said no one is forced to switch to DM
>>> in SPL.
>> This is beside the point, there are boards which use SPL and DM, because
>> the non-DM drivers are steadily going away. So the growth in SPL size is
>> there, either directly or as a side-effect.
>>>>> So it's just debug prints you were doing that ran in
>>>>> to a problem?  Thanks!
>>>> git grep %i indicates ~400 sites where %i is used, so no, not just debug
>>>> prints. All of those are broken. And no, I'm not inclined to patch all
>>>> the code to use %d instead of %i just because handling %i is a problem.
>>> Not all 400 of them but the ones that are expected to be used in SPL and
>>> with TINY_PRINTF need to, yes.  Go look at the git log of tiny-printf.c,
>>> we've changed things around to avoid growth when at all possible.
>> I appreciate that. However, I would also appreciate if printf() behaved
>> in a sane manner, and missing %i support is really weird.
>>> Because yes, I don't want to grow a few hundred boards by 6 bytes when
>>> we have a reasonable alternative.  There's 300 hits, of which a dozen
>>> are non-debug and likely to ever be in SPL code.
>> Why don't we instead replace %d with %i altogether then ? The %d seems
>> to be seldom used outside of U-Boot, where it is only used because of
>> this tiny-printf limitation, while %i is used quite often.
>>> And no, this isn't the
>>> first time I've raised such an issue, it's just the first time you've
>>> been hit by this, sorry.
>> Does this therefore set a precedent that we are allowed to block any and
>> all patches which grow SPL size, no matter how useful they might be ?
> This is following the precedent that was set for tiny printf a while ago
> with some other "it would be nice if..." format that could instead be
> handled differently, again for the case of tiny printf.  It is not
> supposed to cover everything, or most things.  It is supposed to let
> SPL/TPL still have printf in otherwise very tight situations.

Except the way it is right now, a lot of output is broken in SPL in an
inobvious way, which makes working with and/or debugging SPL difficult
and special, compared to U-Boot and other software.

> And as a reminder, I throw every PR through a before/after size check
> and flag growth that's global and not fixing a bug that can't be fixed
> some other way.  Change your prints to %d and fix the problem without a
> size change.

Sorry, no, "change your formatting strings to cater for our broken
printf() implementation" really is not the solution here.

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