Re: [Qemu-devel] [PATCH v1 2/3] arm: fix the armv7m reset state

[KONRAD Frederic <frederic.konrad@adacore.com>]

On 06/29/2017 05:14 PM, Peter Maydell wrote:
> On 29 June 2017 at 10:28, KONRAD Frederic <frederic.konrad@adacore.com> wrote:
>> This fixes an odd bug when a ROM is present somewhere and an alias @0x00000000
>> is pointing to the ROM. The "if (rom)" test fails and we don't get a valid reset
>> state. QEMU later crashes with an exception because the ARMv7-M starts with the
>> ARM instruction set. (eg: PC & 0x01 is 0).
>>
>> This patch uses memory_region_get_offset_within_address_space introduced before
>> to check if an alias doesn't point to a flash somewhere.
>>
>> Signed-off-by: KONRAD Frederic <frederic.konrad@adacore.com>
> 
> This is awkward, because in the "we have a ROM but it's not been
> copied into memory yet" case, the only thing we have is the
> rom->addr, which is the address which the user's ROM blob said
> it ought to be loaded in at. If the user didn't actually provide
> a ROM blob that loads at 0 that seems a bit like a user error,
> and I don't think this patch will catch all the cases of that
> sort of mistake.

I don't think it's really a user mistake because on the real HW
the alias is configurable.. at least in my case.

There is a "jumper" setting to mirror either the Flash or the
SRAM, etc. So the binaries isn't located at 0 but at the flash
address 0x8000000 or some such. That's the case with u-boot and
the precompiled examples I found for this stm32fxxxx board.

  For instance if address 0 is real flash and the
> high address alias is modelled by having the high address be the
> alias, then if the user passes us an ELF file saying "load to
> the high address" then this change won't catch that I think
> (because doing the memory_region_find/get_offset_within_address_space
> will return 0, which has already been tried). You'd need to
> somehow have a way to say "find all the addresses within this
> AS where this MR is mapped" and try them all...

This is more likely to be a user error :). Maybe we can load
the ROM before the reset but that seems a lot more invasive..

BTW isn't there a trick with the ELF entry somewhere? Or is that
for the Cortex-A?

Thanks,
Fred

> 
> thanks
> -- PMM
>