* Re: Initialize RAM from a file and save it to the file
[not found] <CACproumcn8Dba=Mt7ww-uFtb2kHpLsF36j0DiKEKQSVDtMPpcg@mail.gmail.com>
@ 2021-07-19 10:01 ` Philippe Mathieu-Daudé
2021-07-19 13:03 ` Igor Mammedov
0 siblings, 1 reply; 2+ messages in thread
From: Philippe Mathieu-Daudé @ 2021-07-19 10:01 UTC (permalink / raw)
To: Hiroko Shimizu, qemu-discuss; +Cc: Igor Mammedov, qemu-devel
Hi Hiroko,
On 7/19/21 11:34 AM, Hiroko Shimizu wrote:
> Hello,
> I'd like to initialize RAM from a specific file when RAM is created.
> Then, I tried using memory_region_init_ram_from_file().
To load a file after the machine is created and before the VM is started
I use the 'generic loader device'.
> I wonder what file format is necessary. I tried using a binary file,
> however the contents of the file wasn't recognized and file_size(defined
> in qemu_ram_alloc_from_fd()) was zero.
See the doc in docs/system/generic-loader.rst:
The loader device also allows files to be loaded into memory.
It can load ELF, U-Boot, and Intel HEX executable formats as
well as raw images. The syntax is shown below:
-device
loader,file=<file>[,addr=<addr>][,cpu-num=<cpu-num>][,force-raw=<raw>]
> Could you tell me what I need to do or another way to initialize RAM
> from a file?
>
> Also, is it possible to save RAM's value to the file when a value is
> written to RAM which is initialized memory_region_init_ram_from_file()?
2 years ago I was using -mem-path /dev/shm/ (and maybe -mem-prealloc) to
keep the ram sync on a file, pause the VM and analyse the memory, but it
stopped working after the global memdev refactor. I don't think my use
case was the expected one. Maybe I simply need to adapt to a new command
line format :)
Now I use 'pmemsave' from the monitor:
pmemsave addr size file -- save to disk physical memory dump starting at
'addr' of size 'size'
If attached from GDB:
(gdb) monitor pmemsave 0x20000000 0x1000000 /tmp/ram.dump
There are other commands and probably a clever way to do that.
See also the VM snapshot feature, described here, which might be
what you are looking for:
https://translatedcode.wordpress.com/2015/07/06/tricks-for-debugging-qemu-savevm-snapshots/
Regards,
Phil.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Initialize RAM from a file and save it to the file
2021-07-19 10:01 ` Initialize RAM from a file and save it to the file Philippe Mathieu-Daudé
@ 2021-07-19 13:03 ` Igor Mammedov
0 siblings, 0 replies; 2+ messages in thread
From: Igor Mammedov @ 2021-07-19 13:03 UTC (permalink / raw)
To: Philippe Mathieu-Daudé; +Cc: qemu-devel, Hiroko Shimizu, qemu-discuss
On Mon, 19 Jul 2021 12:01:10 +0200
Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
> Hi Hiroko,
>
> On 7/19/21 11:34 AM, Hiroko Shimizu wrote:
> > Hello,
> > I'd like to initialize RAM from a specific file when RAM is created.
> > Then, I tried using memory_region_init_ram_from_file().
...
> > Could you tell me what I need to do or another way to initialize RAM
> > from a file?
> >
> > Also, is it possible to save RAM's value to the file when a value is
> > written to RAM which is initialized memory_region_init_ram_from_file()?
>
> 2 years ago I was using -mem-path /dev/shm/ (and maybe -mem-prealloc) to
> keep the ram sync on a file, pause the VM and analyse the memory, but it
> stopped working after the global memdev refactor. I don't think my use
-mem-path should still work as it's aliased to default memdev,
(see: create_default_memdev), that's assumes legacy CLI and that
board uses MachineState::ram as RAM.
(it certainly worked on mainstream boards, if you share your CLI
I can look if it's expected or a bug).
For new CLI:
it's recommended to use '-machine memory-backend=' which points to previously
specified file backend, ex:
-object memory-backend-file,id=myram,share=yes,size=1G,mem-path=/ram-image-file \
-machine memory-backend=myram
Above will create memory region and assign it to MachineState::ram,
so one should use that instead of manually calling memory_region_init_ram_from_file().
> case was the expected one. Maybe I simply need to adapt to a new command
> line format :)
>
> Now I use 'pmemsave' from the monitor:
>
> pmemsave addr size file -- save to disk physical memory dump starting at
> 'addr' of size 'size'
>
> If attached from GDB:
>
> (gdb) monitor pmemsave 0x20000000 0x1000000 /tmp/ram.dump
>
> There are other commands and probably a clever way to do that.
>
> See also the VM snapshot feature, described here, which might be
> what you are looking for:
> https://translatedcode.wordpress.com/2015/07/06/tricks-for-debugging-qemu-savevm-snapshots/
>
> Regards,
>
> Phil.
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-07-19 10:01 ` Initialize RAM from a file and save it to the file Philippe Mathieu-Daudé
2021-07-19 13:03 ` Igor Mammedov
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