Re: [PATCH] Support SHF_GNU_MBIND and PT_GNU_MBIND_XXX

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Mar 16, 2017 at 8:38 PM, Alan Modra <amodra@gmail.com> wrote:
> On Wed, Mar 15, 2017 at 03:46:17PM -0700, H.J. Lu wrote:
>> Any comments?
>
> Doesn't pass my sniff test.
>
> You say that management of special memory regions doesn't belong in
> the kernel or glibc, but will be handled by a vendor supplied
> library.  In that case, why must ld.so run your magic
> __gnu_mbind_setup function?  If ld.so doesn't need to run

 __gnu_mbind_setup needs to called with memory type, address and
length in executable, DSOs and dlopened DSOs before constructors
are called.

> __gnu_mbind_setup then there's no need to pass information to ld.so
> via special segment types and flags.
>
> Just have the application call __gnu_mbind_setup.  The function
> can take the address range(s) requested as a parameter rather than
> putting them into the executable headers.  It shouldn't be difficult
> for the linker to arrange such a call on application startup.
>

The goal is to place data in special memory sections via attribute.
To place an uninitialized variable, foo, in a mbind bss section with
memory type 1:

int foo __attribute__ ((mbind(0x1)));

To place a variable, foo, in a mbind data section with memory type 2:

int foo __attribute__ ((mbind(0x2))) = 1;

To place a read-only variable, foo, in a mbind rodata section with
memory type 3:

const int foo __attribute__ ((mbind(0x3))) = 1;

How can linker arrange calling __gnu_mbind_setup in executable,
DSOs and dlopened DSOs before constructors are called?


-- 
H.J.