On 6/29/21 4:37 AM, Wolfgang Denk wrote:
Dear Roland,
In message <[email protected]> you
wrote:
U-Boot uses almost everywhere hexadecimal numbers. But some bootargs
passed to Linux are expecting decimal numbers. As long as the values
are in the range 0 to 9 it is sufficient to just strip 0x from the
number. But for greater values a method for converting numbers to
decimal is needed.
This patch adds C like format string capabilities to the setexpr
command. Here are some examples:
Thanks!
In contrast to the original C format strings the number of parameters
is limited to one. As the get_arg() function returns unsigned long
type, the format string commands are limited to those which are
operating on unsigned long type.
These are two pretty unfortunate restrictions. I guess it should
not be too hard to avoid both of these. Can you please give it a
try?
I think it is reasonable to assume (and specify) that, when the
"fmt" option is used, _all_ following arguments will be passed
(unchanged) to the sprintf() function.
This was actually one of my intentions when making this suggestion -
to be able to construct any kind of data from pieces; say, for
example:
=> setexpr foo fmt "%0x08x-%s-%d-%s" $a $b $c $d
Best regards,
Wolfgang Denk
The issue with this is twofold. First, there is no portable way to
construct a va_list from C code. So the likely way to do this would be
to set an arbitrary limit, and then just pass the arguments in. E.g.
something like
snprintf(buf, sizeof(buf), argv[3], argc >= 4 ? argv[4] : NULL, /* etc
*/);
but of course there is no way to check that the format string matches
the correct number of arguments. This is a pretty big footgun.
The other problem is that things like `%d` expect a number and not a
string. So you would have to reimplement snprintf anyway so that it
expects all of its arguments to be strings, and calls strtoul as
appropriate. And considering that the *printf functions take 5k
already, this reimplementation may add a significant amount of code.
For this reason, I'd much prefer to just have `hex` and `dec` functions
which do the appropriate conversions.
--Sean
