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Re: [Qemu-devel] [PATCH v12 2/2] docs: Add a generic loader explanation
From: |
Alistair Francis |
Subject: |
Re: [Qemu-devel] [PATCH v12 2/2] docs: Add a generic loader explanation document |
Date: |
Wed, 5 Oct 2016 14:31:39 -0700 |
On Wed, Oct 5, 2016 at 12:44 AM, Markus Armbruster <address@hidden> wrote:
> Alistair Francis <address@hidden> writes:
>
>> On Tue, Oct 4, 2016 at 12:56 AM, Markus Armbruster <address@hidden> wrote:
>>> Alistair Francis <address@hidden> writes:
>>>
>>>> On Thu, Sep 29, 2016 at 10:36 PM, Markus Armbruster <address@hidden> wrote:
>>>>> Alistair Francis <address@hidden> writes:
>>>>>
>>>>>> On Thu, Sep 29, 2016 at 2:24 AM, Markus Armbruster <address@hidden>
>>>>>> wrote:
>>>>>>> Alistair Francis <address@hidden> writes:
>>>>>>>
>>>>>>>> Signed-off-by: Alistair Francis <address@hidden>
>>>>>>>> Reviewed-by: Peter Maydell <address@hidden>
>>>>>>>> ---
>>>>>>>> V11:
>>>>>>>> - Fix corrections
>>>>>>>> V10:
>>>>>>>> - Split the data loading and PC setting
>>>>>>>> V9:
>>>>>>>> - Clarify the image loading options
>>>>>>>> V8:
>>>>>>>> - Improve documentation
>>>>>>>> V6:
>>>>>>>> - Fixup documentation
>>>>>>>> V4:
>>>>>>>> - Re-write to be more comprehensive
>>>>>>>>
>>>>>>>> docs/generic-loader.txt | 81
>>>>>>>> +++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>> 1 file changed, 81 insertions(+)
>>>>>>>> create mode 100644 docs/generic-loader.txt
>>>>>>>>
>>>>>>>> diff --git a/docs/generic-loader.txt b/docs/generic-loader.txt
>>>>>>>> new file mode 100644
>>>>>>>> index 0000000..d1f8ce3
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/docs/generic-loader.txt
>>>>>>>> @@ -0,0 +1,81 @@
>>>>>>>> +Copyright (c) 2016 Xilinx Inc.
>>>>>>>> +
>>>>>>>> +This work is licensed under the terms of the GNU GPL, version 2 or
>>>>>>>> later. See
>>>>>>>> +the COPYING file in the top-level directory.
>>>>>>>> +
>>>>>>>> +
>>>>>>>> +The 'loader' device allows the user to load multiple images or values
>>>>>>>> into
>>>>>>>> +QEMU at startup.
>>>>>>>> +
>>>>>>>> +Loading Data into Memory Values
>>>>>>>> +---------------------
>>>>>>>> +The loader device allows memory values to be set from the command
>>>>>>>> line. This
>>>>>>>> +can be done by following the syntax below:
>>>>>>>> +
>>>>>>>> + -device loader,addr=<addr>,data=<data>,data-len=<data-len>
>>>>>>>> + [,data-be=<data-be>][,cpu-num=<cpu-num>]
>>>>>>>> +
>>>>>>>> + <addr> - The address to store the data in.
>>>>>>>> + <data> - The value to be written to the address. The maximum
>>>>>>>> size of
>>>>>>>> + the data is 8 bytes.
>>>>>>>> + <data-len> - The length of the data in bytes. This argument must
>>>>>>>> be
>>>>>>>> + included if the data argument is.
>>>>>>>> + <data-be> - Set to true if the data to be stored on the guest
>>>>>>>> should be
>>>>>>>> + written as big endian data. The default is to write
>>>>>>>> little
>>>>>>>> + endian data.
>>>>>>>> + <cpu-num> - The number of the CPU's address space where the
>>>>>>>> data should
>>>>>>>> + be loaded. If not specified the address space of
>>>>>>>> the first
>>>>>>>> + CPU is used.
>>>>>>>> +
>>>>>>>> +For all values both hex and decimal values are allowed. By default
>>>>>>>> the values
>>>>>>>> +will be parsed as decimal. To use hex values the user should prefix
>>>>>>>> the number
>>>>>>>> +with a '0x'.
>>>>>>>
>>>>>>> Unless you bypassed QemuOpts number parsing somehow, octal works as
>>>>>>> well. In case you did bypass: don't! Command line consistency matters.
>>>>>>> Follow-up patch reverting the bypass would be required.
>>>>>>>
>>>>>>> Not sure we want to document QemuOpts number syntax everywhere we
>>>>>>> explain how a certain feature uses the command line. A pointer to the
>>>>>>> canonical place could be better. Anyway, not something that needs
>>>>>>> fixing before we commit.
>>>>>>
>>>>>> I didn't bypass it, octal should work as well. I have clarified that a
>>>>>> bit in the doc.
>>>>>
>>>>> Thanks.
>>>>>
>>>>>>>> +
>>>>>>>> +An example of loading value 0x8000000e to address 0xfd1a0104 is:
>>>>>>>> + -device loader,addr=0xfd1a0104,data=0x8000000e,data-len=4
>>>>>>>> +
>>>>>>>> +Setting a CPU's Program Counter
>>>>>>>> +---------------------
>>>>>>>> +The loader device allows the CPU's PC to be set from the command
>>>>>>>> line. This
>>>>>>>> +can be done by following the syntax below:
>>>>>>>> +
>>>>>>>> + -device loader,addr=<addr>,cpu-num=<cpu-num>
>>>>>>>> +
>>>>>>>> + <addr> - The value to use as the CPU's PC.
>>>>>>>> + <cpu-num> - The number of the CPU whose PC should be set to the
>>>>>>>> + specified value.
>>>>>>>> +
>>>>>>>> +For all values both hex and decimal values are allowed. By default
>>>>>>>> the values
>>>>>>>> +will be parsed as decimal. To use hex values the user should prefix
>>>>>>>> the number
>>>>>>>> +with a '0x'.
>>>>>>>> +
>>>>>>>> +An example of setting CPU 0's PC to 0x8000 is:
>>>>>>>> + -device loader,addr=0x8000,cpu-num=0
>>>>>>>> +
>>>>>>>> +Loading Files
>>>>>>>> +---------------------
>>>>>>>> +The loader device also allows files to be loaded into memory. This
>>>>>>>> can be done
>>>>>>>> +similarly to setting memory values. The syntax is shown below:
>>>>>>>> +
>>>>>>>> + -device
>>>>>>>> loader,file=<file>[,addr=<addr>][,cpu-num=<cpu-num>][,force-raw=<raw>]
>>>>>>>> +
>>>>>>>> + <file> - A file to be loaded into memory
>>>>>>>> + <addr> - The addr in memory that the file should be loaded.
>>>>>>>> This is
>>>>>>>> + ignored if you are using an ELF (unless force-raw
>>>>>>>> is true).
>>>>>>>> + This is required if you aren't loading an ELF.
>>>>>>>> + <cpu-num> - This specifies the CPU that should be used. This is
>>>>>>>> an
>>>>>>>> + optional argument and will cause the CPU's PC to be
>>>>>>>> set to
>>>>>>>> + where the image is stored or in the case of an ELF
>>>>>>>> file to
>>>>>>>> + the value in the header. This option should only be
>>>>>>>> used
>>>>>>>> + for the boot image.
>>>>>>>> + This will also cause the image to be written to the
>>>>>>>> specified
>>>>>>>> + CPU's address space. If not specified, the default
>>>>>>>> is CPU 0.
>>>>>>>
>>>>>>> Using @cpu-num both for further specifying the meaning of @addr and for
>>>>>>> setting that CPU's PC is awkward. Are you sure there will never be a
>>>>>>> use case where you need to specify the CPU without also setting its PC?
>>>>>>>
>>>>>>> To be clear: while I feel this is a question we must discuss and
>>>>>>> resolve, I don't think we need to hold the series for it.
>>>>>>
>>>>>> I agree that this can occur. Internally in the loader framework is a
>>>>>> set_pc variable.
>>>>>>
>>>>>> In the future we can make this user accessible and then allow that to
>>>>>> decide if the PC should be set or not.
>>>>>
>>>>> If you can't do it right away, please document it as restriction, and
>>>>> add a TODO comment to lift it.
>>>>
>>>> I have a patch that adds known restrictions.
>>>>
>>>>>
>>>>>>>> + <force-raw> - Forces the file to be treated as a raw image. This
>>>>>>>> can be
>>>>>>>> + used to specify the load address of ELF files.
>>>>>>>
>>>>>>> "Specifying the load address of an ELF file" sounds like loading a
>>>>>>> position-independent ELF file at a particular address. But I guess this
>>>>>>> is actually for loading a file raw even though it is recognized by QEMU
>>>>>>> as ELF.
>>>>>>
>>>>>> This option basically does make an ELF file position-independent as
>>>>>> the user can control where it is loaded.
>>>>>
>>>>> Aha. Then the name "force-raw" is confusing.
>>>>
>>>> I disagree. It tells QEMU to treat the image as just a dumb blob,
>>>> instead of loading it as and ELF file. I thin force-raw makes sense as
>>>> the user is telling QEMU that the image should be treated as a raw
>>>> image, no matter what it actually is.
>>>
>>> I'm still confused then.
>>>
>>> I can see two possible features here, and based on your documentation
>>> and commentary, I can't tell which one you implemented:
>>>
>>> 0. QEMU can load raw files and ELF executable files. Raw files are
>>> loaded verbatim at a the specified address. ELF executable files are
>>> loaded by an ELF loader, which loads the program header table's loadable
>>> segments.
>>>
>>> 1. force-raw overrides the ELF detection, to let you load an ELF
>>> executable file verbatim, as if it was raw.
>>
>> This is what the option does. It forces the image to be treated as a raw
>> image.
>
> Okay, makes sense now.
>
>> I'm sorry if I implied it was option 2 instead.
>
> No problem. Suggest to clarify docs/generic-loader.txt, perhaps like
> this:
Too easy. I sent a V3 of my docs updating patch which fixes this.
It's called: docs/generic-loader: Update the document
Thanks,
Alistair
>
> Loading Files
> -------------
>
> The loader device also allows files to be loaded into memory. It
> can load raw files and ELF executable files. Raw files are loaded
> verbatim. ELF executable files are loaded by an ELF loader. The
> syntax is shown below:
>
> [...]
> <force-raw> - force-raw=on forces the file to be treated as a raw
> image. This can be used to load ELF files as if
> they were raw.
>