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

hemant at mnkcg.com hemant at mnkcg.com
Fri Jun 9 20:42:50 EDT 2017


Great, thanks, Nate!

 

Hemant

 

From: Nate Foster [mailto:jnfoster at cs.cornell.edu] 
Sent: Friday, June 09, 2017 8:37 PM
To: hemant at mnkcg.com
Cc: Andy Fingerhut <andy.fingerhut at gmail.com>; p4-dev <p4-dev at lists.p4.org>
Subject: Re: [P4-dev] typedef, P4-16 & p4c compiler

 

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 <mailto: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 <mailto: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 <mailto: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 <mailto: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>  [mailto: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 <mailto:andy.fingerhut at gmail.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 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 <mailto:andy.fingerhut at gmail.com> ]
Sent: Thursday, June 08, 2017 8:52 PM
To: hemant at mnkcg.com <mailto:hemant at mnkcg.com> <mailto:hemant at mnkcg.com <mailto:hemant at mnkcg.com> >
Cc: Mihai Budiu <mbudiu at vmware.com <mailto:mbudiu at vmware.com> <mailto:mbudiu at vmware.com <mailto:mbudiu at vmware.com> >>; p4-dev <
p4-dev at lists.p4.org <mailto:p4-dev at lists.p4.org> <mailto: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> <mailto: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> <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> <mailto:hemant at mnkcg.com <mailto:hemant at mnkcg.com> >; 'p4-dev' <
p4-dev at lists.p4.org <mailto:p4-dev at lists.p4.org> <mailto: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> <mailto: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 <mailto:p4-dev at lists.p4.org> >
Cc: Mihai Budiu<mailto:mbudiu at vmware.com <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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