Re: [PATCH] qemu: make version available in coredump

[Laszlo Ersek <lersek@redhat.com>]

On 2/15/23 23:05, Stefan Hajnoczi wrote:
> On Tue, 7 Jun 2022 at 16:33, Vladimir Sementsov-Ogievskiy
> <vsementsov@yandex-team.ru> wrote:
>>
>> Add a variable with QEMU_FULL_VERSION definition. Then the content of
>> the variable is easily searchable:
>>
>>    strings /path/to/core | grep QEMU_FULL_VERSION
>>
>> 'volatile' keyword is used to avoid removing the variable by compiler as
>> unused.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
>> ---
>>
>> Hi all!
>>
>> Probably, I just don't know the correct way to get version from core
>> file. If so, please teach me :)
> 
> I've never hit this issue because bug reports usually include the QEMU
> distro package version. Keeping the version string in the core file
> seems reasonable (unless there is already another way to do this).
> 
> Something I'm curious about: is the coredump guaranteed to contain
> static const variables? I wondered if they might be located in the
> .rodata ELF section and excluded from the coredump because they are
> referenced in the NT_FILE mmap note instead. Maybe volatile prevents
> this?
> 
> I CCed Laszlo because I think he worked on crash dumping in the past
> and might know the answer to my question about coredumps.

Apologies -- I don't know. (But, I see the original problem has been
resolved down-thread!)

[FWIW, I've now grepped the tree for QEMU_FULL_VERSION cursorily, and
I'd say doing something like Vladimir's patch, and then replacing all
the references too, could be a good cleanup. At least personally I'm not
a huge fan of macros that expand to string literals (format strings such
as PRIu32, HWADDR_FMT_plx, DMA_ADDR_FMT etc are exceptions of course).
But this is really just a thought in passing.]

Laszlo

> 
> Stefan
> 
>>
>>  softmmu/vl.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/softmmu/vl.c b/softmmu/vl.c
>> index 4c1e94b00e..1f51a713a0 100644
>> --- a/softmmu/vl.c
>> +++ b/softmmu/vl.c
>> @@ -164,6 +164,19 @@ typedef struct DeviceOption {
>>      QTAILQ_ENTRY(DeviceOption) next;
>>  } DeviceOption;
>>
>> +/*
>> + * qemu_full_version_decl is for debugging. Assume you have coredump file, but
>> + * don't know the version neither have original qemu binary file. You need to
>> + * download a package with corresponding binary (and debug package with
>> + * symbols), but which one? You need the version.
>> + *
>> + * This variable makes it simple to get the version by command
>> + *
>> + *     strings path/to/core | grep QEMU_FULL_VERSION
>> + */
>> +static volatile const char qemu_full_version_decl[] =
>> +    "QEMU_FULL_VERSION: " QEMU_FULL_VERSION;
>> +
>>  static const char *cpu_option;
>>  static const char *mem_path;
>>  static const char *incoming;
>> --
>> 2.25.1
>>
>>
>