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

Andy Fingerhut andy.fingerhut at gmail.com
Fri Jun 9 16:04:19 EDT 2017


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
>>
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>
>
>
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