From: Carlos O'Donell <carlos@redhat.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: 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: <4982fddd-e7bb-e7f1-d2ee-7aa73066bc8e@redhat.com> (raw)
In-Reply-To: <CAMe9rOodZ+UXPFWr_LYQ12Hci_PNLyY1F=FO-yL5N3j_iF69pA@mail.gmail.com>
On 02/23/2017 09:59 PM, H.J. Lu wrote:
>> Why does it run _after_ all shared objects and the executable file are loaded?
>
> Since __gnu_mbind_setup may call any external functions, it can only
> be done after everything is loaded and relocated.
Who defines this function?
Where is it implemented?
What does a typical implementation look like for MCDRAM use?
>> Why not let the dynamic loader choose when it needs to setup the memory?
>
> 1. We want to be able to add support for new type memory by just
> updating the run-time library of __gnu_mbind_setup, instead of
> updating glibc.
Which library defines it?
Can two libraries define it? Does the dynamic loader run every DSO's
version of __gnu_mbind_setup?
> 2. Since __gnu_mbind_setup may depend on other libraries, we
> don't want a simple executable requires libfoo and libbar, in addition
> to glibc, nor make libfoo and libbar part of glibc.
Why can't this be run in a constructor? Is that too late?
This seems like a specialized form of constructor that is guaranteed
to run before all other constructors?
>>> int
>>> __gnu_mbind_setup (unsigned int type, void *addr, size_t length)
>>> {
>>> return 0;
>>> }
>>>
>>> which can be overridden by a different implementation at link-time.
>>
>> What if you _can't_ bind at ADDR?
>
> It happens on systems without special memory. __gnu_mbind_setup
> returns a positive value and ld.so keeps going.
Isn't this a violation of what the application binary requested?
This is a soft-failure that that application doesn't know about.
Might this become a security issue if the application expected the
specific memory type?
>> What if the binding would work if ADD was any value?
>>
>
> GNU_MBIND isn't a LOAD segment, similar to GNU_RELRO:
>
> Program Headers:
> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> LOAD 0x000000 0x00000000 0x00000000 0x54624 0x54624 R E 0x1000
> LOAD 0x054e9c 0x00055e9c 0x00055e9c 0x001b0 0x001b8 RW 0x1000
> DYNAMIC 0x054eac 0x00055eac 0x00055eac 0x00110 0x00110 RW 0x4
> NOTE 0x000114 0x00000114 0x00000114 0x00044 0x00044 R 0x4
> GNU_EH_FRAME 0x048eb8 0x00048eb8 0x00048eb8 0x00ff4 0x00ff4 R 0x4
> GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10
> GNU_RELRO 0x054e9c 0x00055e9c 0x00055e9c 0x00164 0x00164 R 0x1
>
> ADDR contains the start of a memory region within the LOAD segment.
What are the constraints of GNU_MBIND then?
Is it required that it covers only the SHF_GNU_MBIND marked sections which
are part of a PT_LOAD segment?
--
Cheers,
Carlos.
next prev parent reply other threads:[~2017-02-28 16:19 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 ` Carlos O'Donell
2017-01-01 0:00 ` H.J. Lu
2017-01-01 0:00 ` Carlos O'Donell [this message]
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 ` 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
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
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