On 07/06/17 12:16, Marc-André Lureau wrote:
> Add vmcoreinfo ELF note if vmcoreinfo device is ready.
>
> To help the python script, add a little global vmcoreinfo_gdb
> structure, that is populated with vmcoreinfo_gdb_update().
>
> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> ---
> scripts/dump-guest-memory.py | 40 ++++++++++++++++++++++++++++++++++++++++
> hw/acpi/vmcoreinfo.c | 3 +++
> 2 files changed, 43 insertions(+)
>
> diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py
> index f7c6635f15..2dd2ed6983 100644
> --- a/scripts/dump-guest-memory.py
> +++ b/scripts/dump-guest-memory.py
> @@ -14,6 +14,7 @@ the COPYING file in the top-level directory.
> """
>
> import ctypes
> +import struct
>
> UINTPTR_T = gdb.lookup_type("uintptr_t")
>
> @@ -120,6 +121,20 @@ class ELF(object):
> self.segments[0].p_filesz += ctypes.sizeof(note)
> self.segments[0].p_memsz += ctypes.sizeof(note)
>
> +
> + def add_vmcoreinfo_note(self, vmcoreinfo):
> + """Adds a vmcoreinfo note to the ELF dump."""
> + chead = type(get_arch_note(self.endianness, 0, 0))
> + header = chead.from_buffer_copy(vmcoreinfo[0:ctypes.sizeof(chead)])
Maybe it's obvious to others, but I would have been helped a lot if a
comment had explained that you are creating a fake note (with 0 desc
size and 0 name size) to figure out the size of the note header. And
then you copy that many bytes out of the vmcoreinfo ELF note.
> + note = get_arch_note(self.endianness,
> + header.n_namesz - 1, header.n_descsz)
Why the -1?
... I think I'm giving up here for this method. My python is weak and I
can't follow this too well. Please add some comments.
More comments below:
> + ctypes.memmove(ctypes.pointer(note), vmcoreinfo, ctypes.sizeof(note))
> + header_size = ctypes.sizeof(note) - header.n_descsz
> +
> + self.notes.append(note)
> + self.segments[0].p_filesz += ctypes.sizeof(note)
> + self.segments[0].p_memsz += ctypes.sizeof(note)
> +
> def add_segment(self, p_type, p_paddr, p_size):
> """Adds a segment to the elf."""
>
> @@ -505,6 +520,30 @@ shape and this command should mostly work."""
> cur += chunk_size
> left -= chunk_size
>
> + def phys_memory_read(self, addr, size):
> + qemu_core = gdb.inferiors()[0]
> + for block in self.guest_phys_blocks:
> + if block["target_start"] <= addr < block["target_end"]:
Although I don't expect a single read to straddle phys-blocks, I would
prefer if you checked (addr + size) -- and not just addr -- against
block["target_end"].
> + haddr = block["host_addr"] + (addr - block["target_start"])
> + return qemu_core.read_memory(haddr, size)
> +
> + def add_vmcoreinfo(self):
> + if not gdb.parse_and_eval("vmcoreinfo_gdb_helper"):
> + return
> +
> + addr = gdb.parse_and_eval("vmcoreinfo_gdb_helper.vmcoreinfo_addr_le")
> + addr = bytes([addr[i] for i in range(4)])
> + addr = struct.unpack("<I", addr)[0]
> +
> + mem = self.phys_memory_read(addr, 16)
> + (version, addr, size) = struct.unpack("<IQI", mem)
> + if version != 0:
> + return
> +
> + vmcoreinfo = self.phys_memory_read(addr, size)
> + if vmcoreinfo:
> + self.elf.add_vmcoreinfo_note(vmcoreinfo.tobytes())
> +
> def invoke(self, args, from_tty):
> """Handles command invocation from gdb."""
>
> @@ -518,6 +557,7 @@ shape and this command should mostly work."""
>
> self.elf = ELF(argv[1])
> self.guest_phys_blocks = get_guest_phys_blocks()
> + self.add_vmcoreinfo()
>
> with open(argv[0], "wb") as vmcore:
> self.dump_init(vmcore)
> diff --git a/hw/acpi/vmcoreinfo.c b/hw/acpi/vmcoreinfo.c
> index 0ea41de8d9..b6bcb47506 100644
> --- a/hw/acpi/vmcoreinfo.c
> +++ b/hw/acpi/vmcoreinfo.c
> @@ -163,6 +163,8 @@ static void vmcoreinfo_handle_reset(void *opaque)
> memset(vis->vmcoreinfo_addr_le, 0, ARRAY_SIZE(vis->vmcoreinfo_addr_le));
> }
>
> +static VMCoreInfoState *vmcoreinfo_gdb_helper;
> +
> static void vmcoreinfo_realize(DeviceState *dev, Error **errp)
> {
> if (!bios_linker_loader_can_write_pointer()) {
> @@ -181,6 +183,7 @@ static void vmcoreinfo_realize(DeviceState *dev, Error
> **errp)
> return;
> }
>
> + vmcoreinfo_gdb_helper = VMCOREINFO(dev);
> qemu_register_reset(vmcoreinfo_handle_reset, dev);
> }
>
>
I guess we don't build QEMU with link-time optimization at the moment.
With link-time optimization, I think gcc might reasonably optimize away
the assignment to "vmcoreinfo_gdb_helper", and "vmcoreinfo_gdb_helper"
itself. This is why I suggested "volatile":
static VMCoreInfoState * volatile vmcoreinfo_gdb_helper;
Do you think volatile is only superfluous, or do you actively dislike it
for some reason?
Thanks,
Laszlo
