[PATCH v3 2/6] cmd: printf: import busybox-1.33.1 printf.c

[Roland Gaudig (OSS)]

Hi Simon,

On 23.07.21 21:41, Simon Glass wrote:
> On Fri, 23 Jul 2021 at 06:30, Roland Gaudig
> <roland.gaudig-oss at weidmueller.com> wrote:
>>
>> From: Roland Gaudig <roland.gaudig at weidmueller.com>
>>
>> Import printf.c from the Busybox project, which provides Bash like
>> format string handling.
>>
>>   src-url: https://git.busybox.net/busybox/
>>   commit bcc5b0e6caca6c7602a6a41f "Bump version to 1.33.1"
>>   version: 1.33.1
>>
>> Signed-off-by: Roland Gaudig <roland.gaudig at weidmueller.com>
>> ---
>>
>> (no changes since v1)
>>
>>  cmd/printf.c | 455 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 455 insertions(+)
>>  create mode 100644 cmd/printf.c
> 
> I think I missed the discussion on this.

Short summary: We wanted to pass a U-Boot environment variable which
contained a hexadecimal value to the kernel bootargs which required a
decimal value. Therefore I created a dec operator to the setexpr command
for converting a value to decimal. Then came the proposal to use a
format string instead of a dec operator. To keep codesize low I
implemented a very limited version, allowing only one argument. Then
came the request to make it more flexible like its Bash counterpart and
allowing multiple arguments. This is what this version tries to do.

> Why can we not use U-Boot's existing printf()?

The existing printf in the lib directroy implements the C library
function, whereas my cmd printf implements a Bash like printf.
Both are on the first glance similar but behave differently in detail.
The C printf requires, that the requested format matches the type of
the argument. If I for example request a %s format and pass an int
type bad things will happen.

In contrast the shell does not have such a strict concept of types,
when requesting a %d format the argument might contain a string
representing a Number. Therefore the shell printf implementation
has to convert this string first into an integer variable, which
then can be passed to the C lib printf function.

> If we can't, dot we need to remove the existing U-Boot printf()?
> Again, sorry if I missed some discussion.

No, we can't. The cmd printf is only a front-end performing the
necessary conversion. It is relying on the lib printf, which does the
actual work.
 
Regards,
Roland