[llvm-dev] [cfe-dev] proposal - pragma section directive in clang

[Javed Absar via llvm-dev]

Thanks Reid/Jonathon for your replies.


Reid,

An important case against module level flags is that it wont allow changing or  resetting section names e.g.


int a;

#pragma clang section bss = "xyz"

int b;


In case above, users would like to see only 'b' placed in 'xyz' and not 'a' as well.

Link pointed to by Jonathon seems to require same behavior.


Jonathon,

We are happy to revise the spelling to -

#pragma clang section bss = "xyz"

as you propose.

Best Regards, Javed.


From: Jonathan Roelofs <jonathan at codesourcery.com>

Sent: 13 March 2017 18:12:57
To: James Molloy; Reid Kleckner; Javed Absar
Cc: LLVM Dev; nd; cfe-dev at lists.llvm.org
Subject: Re: [llvm-dev] [cfe-dev] proposal - pragma section directive in clang



On 3/10/17 2:47 AM, James Molloy via llvm-dev wrote:
> +llvm-dev properly this time.
>
> On Fri, 10 Mar 2017 at 09:42 James Molloy <james at jamesmolloy.co.uk
> <mailto:james at jamesmolloy.co.uk>> wrote:
>

>
>     The documentation is here:
>     http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0472m/chr1359124985290.html
>
>     ** Proposed syntax and (vague) semantics **
>
>     As this is a new pragma for Clang and isn't ARM-specific, we've
>     invented a less ARM-specific syntax. Bikeshedding is expected and
>     welcome.
>
>       #pragma clang section bss(".mybss") rodata(".myrodata")
>     data(".mydata") text(".mytext")

There's some prior art in the GreenHills compiler too, where the example
above would be spelled:

     #pragma ghs section bss=".mybss", rodata=".myrodata",
data=".mydata", text=".mytext"

Maybe it's worth using that syntax, i.e:

     #pragma clang section bss=".mybss", rodata=".myrodata",
data=".mydata", text=".mytext"

Alternatively, supporting vendor-specific spellings might be useful, if
there's a consistency argument to be made for clang doing it its own way.

Docs are pages 108/109 here:
http://www.ece.ualberta.ca/~cmpe490/documents/ghs/build_arm.pdf


Jon

>
>     The pragma applies to all global variable and function declarations
>     from the pragma to the end of the translation unit. The pragma
>     should ideally be pushable and poppable, but that is outside the
>     scope of this RFC. The pragma also applies to static local
>     declarations within functions.
>
>     All global variables and functions affected by this pragma have
>     their default ELF section destinations changed. Globals with
>     __attribute__((section())) are not affected (the attribute trumps
>     the pragma).
>
>     This pragma is only defined to work sensibly for ELF targets.
>


--
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded
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