[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v1] dump: Set correct vaddr for ELF dump
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH v1] dump: Set correct vaddr for ELF dump |
Date: |
Mon, 7 Jan 2019 19:04:49 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
On 01/07/19 13:14, Marc-André Lureau wrote:
> Hi
>
> On Tue, Dec 25, 2018 at 5:52 PM Jon Doron <address@hidden> wrote:
>>
>> vaddr needs to be equal to the paddr since the dump file represents the
>> physical memory image.
>>
>> Without setting vaddr correctly, GDB would load all the different memory
>> regions on top of each other to vaddr 0, thus making GDB showing the wrong
>> memory data for a given address.
>>
>> Signed-off-by: Jon Doron <address@hidden>
>
> This is a non-trivial patch! (qemu-trivial, please ignore).
>
>> ---
>> dump.c | 4 ++--
>> scripts/dump-guest-memory.py | 1 +
>> 2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/dump.c b/dump.c
>> index 4ec94c5e25..bf77a119ea 100644
>> --- a/dump.c
>> +++ b/dump.c
>> @@ -192,7 +192,7 @@ static void write_elf64_load(DumpState *s, MemoryMapping
>> *memory_mapping,
>> phdr.p_paddr = cpu_to_dump64(s, memory_mapping->phys_addr);
>> phdr.p_filesz = cpu_to_dump64(s, filesz);
>> phdr.p_memsz = cpu_to_dump64(s, memory_mapping->length);
>> - phdr.p_vaddr = cpu_to_dump64(s, memory_mapping->virt_addr);
>> + phdr.p_vaddr = phdr.p_paddr;
>
> This is likely breaking paging=true somehow, which sets
> memory_mapping->virt_addr to non-0.
>
> According to doc "If you want to use gdb to process the core, please
> set @paging to true."
>
> Although I am not able to (gdb) x/10bx 0xa0000 for example on a core
> produced with paging. Not sure why, anybody could help?
>
>> assert(memory_mapping->length >= filesz);
>>
>> @@ -216,7 +216,7 @@ static void write_elf32_load(DumpState *s, MemoryMapping
>> *memory_mapping,
>> phdr.p_paddr = cpu_to_dump32(s, memory_mapping->phys_addr);
>> phdr.p_filesz = cpu_to_dump32(s, filesz);
>> phdr.p_memsz = cpu_to_dump32(s, memory_mapping->length);
>> - phdr.p_vaddr = cpu_to_dump32(s, memory_mapping->virt_addr);
>> + phdr.p_vaddr = phdr.p_paddr;
>>
>> assert(memory_mapping->length >= filesz);
>>
>> diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py
>> index 198cd0fe40..2c587cbefc 100644
>> --- a/scripts/dump-guest-memory.py
>> +++ b/scripts/dump-guest-memory.py
>> @@ -163,6 +163,7 @@ class ELF(object):
>> phdr = get_arch_phdr(self.endianness, self.elfclass)
>> phdr.p_type = p_type
>> phdr.p_paddr = p_paddr
>> + phdr.p_vaddr = p_paddr
>
> With your proposed change though, I can dump memory with gdb...
>
>> phdr.p_filesz = p_size
>> phdr.p_memsz = p_size
>> self.segments.append(phdr)
>> --
>> 2.19.2
>>
>>
>
>
I've never used paging-enabled dumps. First, because doing so requires
QEMU to trust guest memory contents (see original commit 783e9b4826b9;
or more recently/generally, the @dump-guest-memory docs in
"qapi/misc.json"). Second, because whenever I had to deal with guest
memory dumps, I always used "crash" (which needs no paging), and the
subject guests were all Linux.
I can't comment on paging-enabled patches for dump, except that they
shouldn't regress the paging-disabled functionality. :) If the patches
satisfy that, I'm fine.
(I *am* surprised that GDB insists on p_vaddr equaling p_paddr; after
all, in the guest, the virtual address is "memory_mapping->virt_addr".
But, I would never claim to understand most of the ELF intricacies,
and/or what GDB requires on top of those.)
Thanks
Laszlo