[PATCH] GSoC: Cache configurations Raspberry Pi 2 support
Gedare Bloom
gedare at gwu.edu
Tue Aug 11 14:00:01 UTC 2015
On Tue, Aug 11, 2015 at 9:59 AM, Gedare Bloom <gedare at gwu.edu> wrote:
> Yeah until you or someone can figure out how to get the .ARM.exidx
> section from being placed in the .bss, a quick work-around would be to
> provide an alternate code to clear the bss that does something like...
>
> memset(bsp_section_bss_begin, 0, __exidx_start - bsp_section_bss_begin);
> memset(__exidx_start, 0, bsp_section_bss_end);
>
Let me be clear, this is a hack but hopefully will get you past the exception.
> On Tue, Aug 11, 2015 at 9:32 AM, Rohini Kulkarni <krohini1593 at gmail.com> wrote:
>> OK! So is there any immediate solution which can be tried?
>>
>> On Tue, Aug 11, 2015 at 6:32 PM, Gedare Bloom <gedare at gwu.edu> wrote:
>>>
>>> I can see the following pertinent information:
>>> [15] .bss NOBITS 001156e0 0a8fd8 00fab0 00 WA 0
>>> 0 32
>>> The bss section starts at 0x1156e0, has size 0xfab0, and is writeable.
>>>
>>> In the symbol table we can see:
>>>
>>> 7825: 001156e0 0 NOTYPE GLOBAL DEFAULT 15 bsp_section_bss_begin
>>> The bsp_section_bss_begin variable has value 0x1156e0, this is good.
>>>
>>> 8729: 0000fab0 0 NOTYPE GLOBAL DEFAULT ABS bsp_section_bss_size
>>> The bsp_section_bss_size is 0xfab0, which is also good.
>>>
>>> Looking at the segments I see one possible oddity. Look at the first and
>>> last
>>> Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
>>> EXIDX 0x0a3fb8 0x001106b8 0x001106b8 0x00008 0x00008 R 0x4
>>> LOAD 0x093900 0x00100000 0x00100000 0x156d8 0x7efc000 RW 0x20
>>>
>>> The first one starts inside of the second! This could well be the
>>> reason for your problem. The .ARM.exidx section is being define
>>> read-only, and is being put into a segment that overlaps with the
>>> segment that catches most of the RW memory.
>>>
>>> Gedare
>>>
>>> On Mon, Aug 10, 2015 at 4:23 PM, Rohini Kulkarni <krohini1593 at gmail.com>
>>> wrote:
>>> > I did a readelf on the rki elf. I have attached the file. Is this
>>> > information helping in anyway?
>>> >
>>> > On Wed, Aug 5, 2015 at 9:16 PM, Gedare Bloom <gedare at gwu.edu> wrote:
>>> >>
>>> >> In arm/shared/startup/linkcmds.base these barriers are used to add
>>> >> gaps in the memory layout at link-time to accommodate for the size
>>> >> requirements of the MMU. xbarrier aligns the executable region,
>>> >> robarrier aligns the read-only memory, and rwbarrier aligns the
>>> >> read-write memory.
>>> >>
>>> >> On Tue, Aug 4, 2015 at 6:23 PM, Rohini Kulkarni <krohini1593 at gmail.com>
>>> >> wrote:
>>> >> >
>>> >> >
>>> >> > On Wed, Aug 5, 2015 at 1:47 AM, Gedare Bloom <gedare at gwu.edu> wrote:
>>> >> >>
>>> >> >> On Tue, Aug 4, 2015 at 2:18 PM, Rohini Kulkarni
>>> >> >> <krohini1593 at gmail.com>
>>> >> >> wrote:
>>> >> >> >
>>> >> >> >
>>> >> >> > On Tue, Jul 28, 2015 at 5:51 AM, Pavel Pisa
>>> >> >> > <ppisa4lists at pikron.com>
>>> >> >> > wrote:
>>> >> >> >>
>>> >> >> >> Hello Rohini and Gedare,
>>> >> >> >>
>>> >> >> >> On Friday 24 of July 2015 15:33:03 Gedare Bloom wrote:
>>> >> >> >> > What are the values of bsp_section_bss_begin, and
>>> >> >> >> > bsp_section_bss_size?
>>> >> >> >> >
>>> >> >> >> > Apparently, the memset is trying to write into the .text (code)
>>> >> >> >> > section, which is a very bad thing to do indeed.
>>> >> >> >> >
>>> >> >> >>
>>> >> >> >> Qiao Yang in RPi 1 BSP now works in the similar
>>> >> >> >> area to enable right graphic memory mapping.
>>> >> >> >>
>>> >> >> >> So my guess is that there could be problem caused
>>> >> >> >> by used MMU mode granularity, which is is 1 MB so
>>> >> >> >> if RO and RW sections are present in the same 1MB
>>> >> >> >> aligned block ten there can be problem. It depends
>>> >> >> >> which section is filled the first. If data and then
>>> >> >> >> text (RO) the troubles begin. If the order is vice
>>> >> >> >> versa then some part of text can be RW instead of RO,
>>> >> >> >> but it should work and cache should not be a problem.
>>> >> >> >>
>>> >> >> >> But I have not dig into this case too much.
>>> >> >> >> Only short glimpse.
>>> >> >> >>
>>> >> >> >> One option is to define 1 MB alignment between text
>>> >> >> >> ad data for RPi case. There is quite a lot of memory
>>> >> >> >> when compared to most RTEMS embedded targets to the
>>> >> >> >> waste is not so important.
>>> >> >> >
>>> >> >> >
>>> >> >> > I didn't quite get what this means. I have no clue on how to
>>> >> >> > proceed
>>> >> >> > with
>>> >> >> > this.
>>> >> >> The MMU defines memory regions in 1MB chunks. Each chunk can have
>>> >> >> its
>>> >> >> own permissions (read-only, or read-write) set. If the .text and
>>> >> >> .data
>>> >> >> (or some other section) overlaps in the same 1MB chunk, and the
>>> >> >> wrong
>>> >> >> permission gets set, then there can be a problem e.g. part of .data
>>> >> >> might be RO or part of .text might be RW.
>>> >> >>
>>> >> >> Did you try the code Sebastian posted? to change the robarrier to
>>> >> >> rwbarrier?
>>> >> >
>>> >> >
>>> >> > What exactly are these barriers?
>>> >> >>
>>> >> >>
>>> >> >> Gedare
>>> >> >>
>>> >> >> >>
>>> >> >> >>
>>> >> >> >> Best wishes,
>>> >> >> >>
>>> >> >> >> Pavel
>>> >> >> >>
>>> >> >> >> On Friday 24 of July 2015 21:55:00 Rohini Kulkarni wrote:
>>> >> >> >> > Hi,
>>> >> >> >> >
>>> >> >> >> > I have attached the report containing outputs of
>>> >> >> >> > arm-rtems4.11-size
>>> >> >> >> > and
>>> >> >> >> > arm-rtems4.11-nm -S.
>>> >> >> >> >
>>> >> >> >> > From arm-rtems4.11-nm -S I don't see how memset() is accessing
>>> >> >> >> > .text
>>> >> >> >> > section. The start and end values for both are not overlapping.
>>> >> >> >> >
>>> >> >> >> > On Fri, Jul 24, 2015 at 7:03 PM, Gedare Bloom <gedare at gwu.edu>
>>> >> >> >> > wrote:
>>> >> >> >> > > On Fri, Jul 24, 2015 at 3:30 AM, Rohini Kulkarni
>>> >> >> >> > > <krohini1593 at gmail.com>
>>> >> >> >> > >
>>> >> >> >> > > wrote:
>>> >> >> >> > > > On 24 Jul 2015 12:35, "Sebastian Huber" <
>>> >> >> >> > >
>>> >> >> >> > > sebastian.huber at embedded-brains.de>
>>> >> >> >> > >
>>> >> >> >> > > > wrote:
>>> >> >> >> > > >> On 23/07/15 23:24, Rohini Kulkarni wrote:
>>> >> >> >> > > >>> I could finally get back to this issue. I used Pi 1 for
>>> >> >> >> > > >>> debugging,
>>> >> >> >> > > >>> but the reason for this problem will apply to Pi 2 also.
>>> >> >> >> > > >>> With text section set to ARMV7_MMU_CODE_CACHED ( which
>>> >> >> >> > > >>> implies
>>> >> >> >> > > >>> read
>>> >> >> >> > >
>>> >> >> >> > > only)
>>> >> >> >> > >
>>> >> >> >> > > >>> , a data abort exception occurs with memset() inside
>>> >> >> >> > >
>>> >> >> >> > > bsp_start_clear_bss()
>>> >> >> >> > >
>>> >> >> >> > > >>> function. An illegal write access to an address according
>>> >> >> >> > > >>> to
>>> >> >> >> > > >>> me.
>>> >> >> >> > > >>
>>> >> >> >> > > >> Which exception and which address? Something is not
>>> >> >> >> > > >> working
>>> >> >> >> > > >> here.
>>> >> >> >> > > >
>>> >> >> >> > > > This is a part of the debugging output. When I used
>>> >> >> >> > >
>>> >> >> >> > > ARMV7_MMU_CODE_CACHED.
>>> >> >> >> > >
>>> >> >> >> > > > (gdb) s
>>> >> >> >> > > > bsp_start_clear_bss ()
>>> >> >> >> > > > at
>>> >> >> >> > > > ../../../../../.././raspberrypi/lib/include/bsp/start.h:126
>>> >> >> >> > > > 126 memset(bsp_section_bss_begin, 0, (size_t)
>>> >> >> >> > > > bsp_section_bss_size);
>>> >> >> >> > >
>>> >> >> >> > > What are the values of bsp_section_bss_begin, and
>>> >> >> >> > > bsp_section_bss_size?
>>> >> >> >> > >
>>> >> >> >> > > Apparently, the memset is trying to write into the .text
>>> >> >> >> > > (code)
>>> >> >> >> > > section, which is a very bad thing to do indeed.
>>> >> >> >> > >
>>> >> >> >> > > > (gdb) s
>>> >> >> >> > > > memset (m=0x1157e0, c=0, n=64176)
>>> >> >> >> > > > at
>>> >> >> >> > > > ../../../../../gcc-4.9.2/newlib/libc/string/memset.c:59
>>> >> >> >> > > > 59 ../../../../../gcc-4.9.2/newlib/libc/string/memset.c:
>>> >> >> >> > > > No
>>> >> >> >> > > > such
>>> >> >> >> > > > file
>>> >> >> >> > >
>>> >> >> >> > > or
>>> >> >> >> > >
>>> >> >> >> > > > directory.
>>> >> >> >> > > > (gdb) s
>>> >> >> >> > > > 49 in
>>> >> >> >> > > > ../../../../../gcc-4.9.2/newlib/libc/string/memset.c
>>> >> >> >> > > > (gdb) s
>>> >> >> >> > > > _ARMV4_Exception_data_abort_default ()
>>> >> >> >> > > > at
>>> >> >> >> > >
>>> >> >> >> > >
>>> >> >> >> > >
>>> >> >> >> > >
>>> >> >> >> > >
>>> >> >> >> > > ../../../../../../../../rtems-local/rtems/c/src/../../cpukit/score/cpu/ar
>>> >> >> >> > >m/armv4-exception-default.S:71
>>> >> >> >> > >
>>> >> >> >> > > > 71 sub sp, #MORE_CONTEXT_SIZE
>>> >> >> >> > > >
>>> >> >> >> > > > When I set text section flag to ARMV7_MMU_READ_WRITE, the
>>> >> >> >> > > > system
>>> >> >> >> > > > starts
>>> >> >> >> > > > successfully.
>>> >> >> >> > > >
>>> >> >> >> > > >> --
>>> >> >> >> > > >> Sebastian Huber, embedded brains GmbH
>>> >> >> >> > > >>
>>> >> >> >> > > >> Address : Dornierstr. 4, D-82178 Puchheim, Germany
>>> >> >> >> > > >> Phone : +49 89 189 47 41-16
>>> >> >> >> > > >> Fax : +49 89 189 47 41-09
>>> >> >> >> > > >> E-Mail : sebastian.huber at embedded-brains.de
>>> >> >> >> > > >> PGP : Public key available on request.
>>> >> >> >> > > >>
>>> >> >> >> > > >> Diese Nachricht ist keine geschäftliche Mitteilung im
>>> >> >> >> > > >> Sinne
>>> >> >> >> > > >> des
>>> >> >> >> > > >> EHUG.
>>> >> >> >> > > >
>>> >> >> >> > > > _______________________________________________
>>> >> >> >> > > > devel mailing list
>>> >> >> >> > > > devel at rtems.org
>>> >> >> >> > > > http://lists.rtems.org/mailman/listinfo/devel
>>> >> >> >>
>>> >> >> >
>>> >> >> >
>>> >> >> >
>>> >> >> > --
>>> >> >> > Rohini Kulkarni
>>> >> >> >
>>> >> >> > _______________________________________________
>>> >> >> > devel mailing list
>>> >> >> > devel at rtems.org
>>> >> >> > http://lists.rtems.org/mailman/listinfo/devel
>>> >> >
>>> >> >
>>> >> >
>>> >> >
>>> >> > --
>>> >> > Rohini Kulkarni
>>> >
>>> >
>>> >
>>> >
>>> > --
>>> > Rohini Kulkarni
>>> >
>>> > _______________________________________________
>>> > devel mailing list
>>> > devel at rtems.org
>>> > http://lists.rtems.org/mailman/listinfo/devel
>>
>>
>>
>>
>> --
>> Rohini Kulkarni
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