Re: [PATCH bpf-next v2 2/3] bpf: btf: add btf print functionality

On Tue, Jul 03, 2018 at 04:33:50PM -0700, Martin KaFai Lau wrote:

On Tue, Jul 03, 2018 at 03:38:43PM -0700, Jakub Kicinski wrote:

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On Tue, 3 Jul 2018 15:23:31 -0700, Jakub Kicinski wrote:

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+			else
+				jsonw_printf(jw, "%hhd", *((char *)data));    

... I think you need to always print a string, and express it as
\u00%02hhx for non-printable.    

Okay that makes sense  

Yeah, IDK, char can be used as a byte as well as a string.  In eBPF
it may actually be more likely to just be used as a raw byte buffer...

Actually, what is the definition/purpose of BTF_INT_CHAR?  There seems
to be no BTF_INT_SHORT and BTF_INT_SIGNED can simply be of size 8...
Is normal int only used for bitfields of size 8 and BTF_INT_CHAR for
char variables?

The kernel seems to be rejecting combinations of those flags, is
unsigned char going to not be marked as char then?

BTF_INT_ENOCODING (CHAR/SIGNED/BOOL) is for formatting (e.g. pretty
print).  It is mainly how CTF is using it also.  Hence, BTF_INT_ENCODINGs
is not a 1:1 mapping to C integer types.
The size of an interger is described by BTF_INT_BITS instead.  

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Either way I think it may be nice to keep it consistent, at least for
the JSON output could we do either always ints or always characters?

for !isprint() case, will "\x%02hhx" make more sense?