Re: [PATCH iproute2 v2] json_print: Fix hidden 64-bit type promotion

On Wed, 25 Apr 2018 16:57:52 +0200
Toke Høiland-Jørgensen [off-list ref] wrote:

Stephen Hemminger [off-list ref] writes:

quoted

On Wed, 25 Apr 2018 16:30:22 +0200
Toke Høiland-Jørgensen [off-list ref] wrote:
 

quoted

print_uint() will silently promote its variable type to uint64_t, but there
is nothing that ensures that the format string specifier passed along with
it fits (and the function name suggest to pass "%u").

Fix this by changing print_uint() to use a native 'unsigned int' type, and
introduce a separate print_u64() function for printing 64-bit values. All
call sites that were actually printing 64-bit values using print_uint() are
converted to use print_u64() instead.

Since print_int() was already using native int types, just add a
print_s64() to match, but don't convert any call sites.

Cc: Kevin Darbyshire-Bryant <redacted>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>  

Yes, this makes sense. Maybe there should be a print_luint for
consistency.  

I just realised I missed a few call sites, so I'll resend. Should I
call the new function print_luint() instead of print_u64()?

Ideally, there would be both functions, and use based on what is being printed.

quoted

Also, I tried (in vain) to make a version that allows GCC to check the
format string.  But it was a struggle and just gave up.  

Yeah, no idea how to do this either...

Maybe some magic smatch or multi-line regex it would be possible to
find all instances of print_uint, then look at format string of each and see if there is
a single %u.  Some added complexity since some places only print json and don't care
and pass NULL for format.