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

Nate Foster jnfoster at cs.cornell.edu
Fri Jun 9 20:36:49 EDT 2017


Keywords are defined in the lexer:

https://github.com/p4lang/p4c/blob/master/frontends/parsers/p4/p4lexer.ll#L82

-N

On Fri, Jun 9, 2017 at 2:16 PM, <hemant at mnkcg.com> wrote:

> 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:heman
>>>> t 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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