[PATCH] tiny-printf: Add support for upper case hex values

[Tom Rini]

On Thu, Mar 20, 2025 at 03:14:03PM +0100, Marek Vasut wrote:
> On 3/20/25 3:00 PM, Quentin Schulz wrote:
> > Hi Marek,
> > 
> > On 3/20/25 12:49 PM, Marek Vasut wrote:
> > > On 3/20/25 11:23 AM, Christoph Niedermaier wrote:
> > > > If tiny printf is used with 0x%08X (upper case X) the output is
> > > > always 0x00000000. It could be confusing if upper case instead
> > > > of lower case is used intentionally or accidentally because the
> > > > actual value is not output. To avoid this confusion, tiny printf
> > > > is extended to support also the formatting with %X.
> > > > 
> > > > Signed-off-by: Christoph Niedermaier <cniedermaier at dh-electronics.com>
> > > TINY_PRINTF is meant to be tiny, i.e. not consume a lot of space, at
> > > the expense of functionality. This is meant to be used in size
> > > constrained environments, like the SPL. If you need full vsprintf()
> > > formatting support, disable TINY_PRINTF in your config and use the
> > > regular vsprintf() implementation.
> > 
> > The issue is that disabling TINY_PRINTF may not be possible (size
> > constraints) and some code is compiled for different stages and people
> > typically don't check whether the format used in printf is valid with
> > tiny_printf. I've had this issue already in the past, I vaguely recall
> > "complaining" about it on IRC.
> > 
> > Maybe there's something we can do to verify that the code is working how
> > we expect it to work, regardless of tiny_printf/full printf selection?
> > checkpatch or a compile-time check for the formats maybe?
> > 
> > But yeah, essentially the whole thing is... if we continue like this,
> > we'll just end up getting closer and closer to the full printf which is
> > not something we want :)
> Shall we maybe patch tiny printf to print '?' on unsupported formatting
> characters, or outright complain that users should fix their code ?

This sounds good to me, adding ? in the output.

> For the %x/%X thing, we could technically fall back from %X to %x , which
> would do the printing with minimum footprint increase, albeit slightly
> malformed:

There's 109 hits on "%X" and another 489 on "%0.X", so I think it's
reasonable to do either of:
- Misprint A-F as a-f (in other words, treat it like 'x'
- Audit the callers and change them to 'x' from 'X'. We normally don't
  capitalize the output and there's all sorts of patches over the years
  changing them to lowercase in other places.

We have done both for other format specifiers and tiny-printf before in
the past.

-- 
Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 659 bytes
Desc: not available
URL: <https://lists.denx.de/pipermail/u-boot/attachments/20250320/e5c93954/attachment.sig>