Re: [Qemu-trivial] [Qemu-devel] [PATCH v1] dump: Set correct vaddr for ELF dump

[Marc-André Lureau]

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
>
>


-- 
Marc-André Lureau