From: "H.J. Lu" <hjl.tools@gmail.com>
To: Suprateeka R Hegde <hegdesmailbox@gmail.com>
Cc: "Carlos O'Donell" <carlos@redhat.com>, gnu-gabi@sourceware.org
Subject: Re: RFC: ABI support for special memory area
Date: Sun, 01 Jan 2017 00:00:00 -0000 [thread overview]
Message-ID: <CAMe9rOoQUFJBmcBp-3vdi-MTWq_K+3z+9sfD3os7r_OTaRnVkQ@mail.gmail.com> (raw)
In-Reply-To: <35fce20b-20e0-3d0e-1957-f3df124a05ac@gmail.com>
On Fri, Mar 31, 2017 at 6:44 AM, Suprateeka R Hegde
<hegdesmailbox@gmail.com> wrote:
> On 30-Mar-2017 10:10 PM, H.J. Lu wrote:
>>> However, I am just thinking that your earlier approach --
>>> __gnu_mbind_setup -- is better when shared libraries with GNU_MBIND
>>> segments are dlopen'ed. They dont have to iterate all over again to
>>> reach their PHDR. Or what is the recommendation for such dlopen'ed
>>> libraries?
>>
>> It is true that dl_iterate_phdr is called by every shared object, dlopened or
>> not, to locate its own PHDR.
>
> Lets put a one liner on best practices or guideline kind of. You have
> already made it clear in the example code. I am just thinking of putting
> them in words too.
>
> Lets say something like, each load module is expected to process only
> its special memory segments. To mean that shlibs/exe need not do any
> book-keeping to avoid multiple executions of the special memory setup
> for the same load module.
>
>>> And this dl_iterate_phdr(3) not being part of any standards, may change
>>> in a totally incompatible way in the future.
>>>
>>
>> dl_iterate_phdr isn't in any standard. But it is in glibc. Given that my
>> proposal is a GNU extension, it isn't a major issue. Working with
>> existing glibc is a big plus.
>
> Awesome. Looks great. Thanks a lot for the new approach.
>
> --
> Supra
Here is the updated proposal.
Thanks.
--
H.J.
--
ABI support for special memory area
To section attributes, add
#define SHF_GNU_MBIND 0x00100000
for sections used to place data or text into a special memory area.
The section names should start with ".mbind" so that they won't be
grouped together with normal sections by link editor. The sh_info
field indicates the special memory type. SHF_GNU_MBIND is only
applicable to SHF_ALLOC sections.
The following memory types in the sh_info field are defined:
/* The highest bandwidth memory. */
#define GNU_MBIND_HBW 0
To the "Program Header" section, add an inclusive range of segment types
for GNU_MBIND segments:
#define PT_GNU_MBIND_NUM 4096
#define PT_GNU_MBIND_LO (PT_LOOS + 0x474e555)
#define PT_GNU_MBIND_HI (PT_GNU_MBIND_LO + PT_GNU_MBIND_NUM - 1)
The array element specifies the location and size of a special memory area.
Each GNU_MBIND segment contains one GNU_MBIND section and the segment
type is PT_GNU_MBIND_LO plus the sh_info value. If the sh_info value is
greater than PT_GNU_MBIND_NUM, no GNU_MBIND segment will be created. Each
GNU_MBIND segment must be aligned at page boundary. The interpretation of
the special memory area information is implementation-dependent.
Implementations may ignore GNU_MBIND segment.
Run-time support
Each load module is expected to process only its special memory segments.
There is no need for executable and shared objects to do any book-keeping
to avoid multiple executions of the special memory setup for the same
load module.
dl_iterate_phdr in the the GNU C library:
int dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
size_t size, void *data),
void *data);
is called via the .init_array section to process GNU_MBIND segments in
executable and shared objects:
static int
callback (struct dl_phdr_info *info, size_t size, void *data)
{
Compute the load address of the current module.
if info->dlpi_addr == the load address of the current module
{
check ELF program headers and process GNU_MBIND segments
return 1;
}
return 0;
}
static void
call_gnu_mbind_setup (void)
{
dl_iterate_phdr (callback, NULL);
}
static void (*init_array) (void)
__attribute__ ((section (".init_array"), used))
= &call_gnu_mbind_setup;
next prev parent reply other threads:[~2017-03-31 15:11 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-01 0:00 H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Carlos O'Donell
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H.J. Lu [this message]
2017-01-01 0:00 ` Florian Weimer
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Florian Weimer
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Florian Weimer
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Carlos O'Donell
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Carlos O'Donell
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Florian Weimer
2017-01-01 0:00 ` H.J. Lu
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