[P4-dev] typedef, P4-16 & p4c compiler

hemant at mnkcg.com hemant at mnkcg.com
Fri Jun 9 17:16:19 EDT 2017


I am aware of the core.p4 file and the p4c compiler.  I am actually  
using the compiler and it's working out great.  I have poked around  
some in the p4c compiler source and could not find the header  
definition yet.

Hemant

Quoting Andy Fingerhut <andy.fingerhut at gmail.com>:

> There is an open source P4 compiler written in C++ here:
> https://github.com/p4lang/p4c
>
> For P4-16 there is a small core.p4 include file used in pretty much every
> P4-16 program, but it doesn't 'define' struct or header keywords.  Those
> are hard-coded into the compiler.
> https://github.com/p4lang/p4c/blob/master/p4include/core.p4
>
> Andy
>
> On Fri, Jun 9, 2017 at 11:21 AM, <hemant at mnkcg.com> wrote:
>
>> Agree.  I was only pointing out that a keyword can be typedefed if the
>> keyword is also a type.  It's the struct that is the issue - I am all set.
>> Is the source to the P4 library that supports keywords available anywhere
>> so that we could see how is the header defined?
>>
>> Thanks,
>>
>> Hemant
>>
>>
>> Quoting Mihai Budiu <mbudiu at vmware.com>:
>>
>> int is a keyword, but it is also a type.
>>> struct is not a type. The same holds for header in P4.
>>>
>>> Mihai
>>>
>>> From: hemant at mnkcg.com [mailto:hemant at mnkcg.com]
>>> Sent: Friday, June 9, 2017 2:54 AM
>>> To: 'Andy Fingerhut' <andy.fingerhut at gmail.com>
>>> Cc: Mihai Budiu <mbudiu at vmware.com>; 'p4-dev' <p4-dev at lists.p4.org>
>>> Subject: RE: [P4-dev] typedef, P4-16 & p4c compiler
>>>
>>> I do know the header is a keyword in P4-16, but so are int and long in
>>> C.  The C preprocessor totally allows, for example, a “typedef int
>>> distance;”.   The issue is because the header may be like a struct in C.
>>>  My use case is typedef a new type from a header and then use the new type
>>> as several headers with different set of bits.
>>>
>>> Hemant
>>>
>>> From: Andy Fingerhut [mailto:andy.fingerhut at gmail.com]
>>> Sent: Thursday, June 08, 2017 8:52 PM
>>> To: hemant at mnkcg.com<mailto:hemant at mnkcg.com>
>>> Cc: Mihai Budiu <mbudiu at vmware.com<mailto:mbudiu at vmware.com>>; p4-dev <
>>> p4-dev at lists.p4.org<mailto:p4-dev at lists.p4.org>>
>>> Subject: Re: [P4-dev] typedef, P4-16 & p4c compiler
>>>
>>> I believe the string "header" is a keyword in P4-16, and probably cannot
>>> be the name of a type.
>>>
>>> You can define a header type with name "ipv4_t", and then typedef another
>>> type name to be the same as that one like so:
>>>
>>> header ipv4_t {
>>>     // your fields here
>>> }
>>> typedef ipv4_t another_type_name_t;
>>>
>>> then use 'another_type_name_t' any place that you would otherwise use
>>> 'ipv4_t'.
>>>
>>> Andy
>>>
>>> On Thu, Jun 8, 2017 at 1:42 PM, <hemant at mnkcg.com<mailto:hemant at mnkcg.com>>
>>> wrote:
>>> typedef header foo_t;
>>>
>>> From: Mihai Budiu [mailto:mbudiu at vmware.com<mailto:mbudiu at vmware.com>]
>>> Sent: Thursday, June 08, 2017 4:40 PM
>>> To: hemant at mnkcg.com<mailto:hemant at mnkcg.com>; 'p4-dev' <
>>> p4-dev at lists.p4.org<mailto:p4-dev at lists.p4.org>>
>>> Subject: RE: typedef, P4-16 & p4c compiler
>>>
>>> Can you post a code fragment (even if it does not work) showing what you
>>> want to achieve?
>>>
>>> Mihai
>>>
>>> From: hemant at mnkcg.com<mailto:hemant at mnkcg.com>
>>> Sent: Thursday, June 8, 2017 1:19 PM
>>> To: 'p4-dev'<mailto:p4-dev at lists.p4.org>
>>> Cc: Mihai Budiu<mailto:mbudiu at vmware.com>
>>> Subject: typedef, P4-16 & p4c compiler
>>>
>>> If C preprocessing is supported in P4, including P4-16, is the P4-16
>>> “header” possible to be typedefed?  I am not sure what the type is because
>>> the header is in the P4 library.  If a C preprocessor allows any C type
>>> such as “int” to be typdefed, why not the P4-16 header?
>>>
>>> Thanks,
>>>
>>> Hemant
>>>
>>> _______________________________________________
>>> P4-dev mailing list
>>> P4-dev at lists.p4.org<mailto:P4-dev at lists.p4.org>
>>> http://lists.p4.org/mailman/listinfo/p4-dev_lists.p4.org<htt
>>> ps://urldefense.proofpoint.com/v2/url?u=http-3A__lists.p4.
>>> org_mailman_listinfo_p4-2Ddev-5Flists.p4.org&d=DwMFaQ&c=
>>> uilaK90D4TOVoH58JNXRgQ&r=tGW6TKXajnoXSyy1S1P4DHGPe8sj54GGvw-
>>> b21n7aWg&m=rBRTqD1_dhDUOEybSy05BurT1i2E_alMsKeGQNHNRPU&s=0oc
>>> Byjszt6s5iCDdhYiYJCA2vSMV-Z6sLSqtYbL-S1I&e=>
>>>
>>
>>
>>






More information about the P4-dev mailing list