Re: [PATCH] gdb-xml: Fix size of EFER register on i386 architecture when debugged by GDB

[Alex Bennée]

TaiseiIto <taisei1212@outlook.jp> writes:

> Before this commit, there were contradictory descriptions about size of EFER
> register.
> Line 113 says the size is 8 bytes.
> Line 129 says the size is 4 bytes.
>
> As a result, when GDB is debugging an OS running on QEMU, the GDB cannot
> read 'g' packets correctly. This 'g' packet transmits values of each
> registers of machine emulated by QEMU to GDB. QEMU, the packet sender,
> assign 4 bytes for EFER in 'g' packet based on the line 113.
> GDB, the packet receiver, extract 8 bytes for EFER in 'g' packet based on
> the line 129. Therefore, all registers located behind EFER in 'g' packet
> has been shifted 4 bytes in GDB.

I can't get the failure to read in my case:

  ./qemu-system-i386 -monitor none -display none \
    -chardev stdio,id=out -device isa-debugcon,chardev=out \
    -device isa-debug-exit,iobase=0xf4,iosize=0x4 \
    -kernel ./tests/tcg/i386-softmmu/memory -s -S

and then with gdb:

  ➜  gdb ./tests/tcg/i386-softmmu/memory -ex "target remote localhost:1234"
  Reading symbols from ./tests/tcg/i386-softmmu/memory...
  Remote debugging using localhost:1234
  0x0000fff0 in ?? ()
  (gdb) info registers efer
  efer           0x0                 [ ]

What am I missing?

>
> After this commit, GDB can read 'g' packets correctly.
>
> Signed-off-by: TaiseiIto <taisei1212@outlook.jp>
> ---
>  gdb-xml/i386-32bit.xml | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdb-xml/i386-32bit.xml b/gdb-xml/i386-32bit.xml
> index 872fcea9c2..7a66a02b67 100644
> --- a/gdb-xml/i386-32bit.xml
> +++ b/gdb-xml/i386-32bit.xml
> @@ -110,7 +110,7 @@
>       <field name="PKE" start="22" end="22"/>
>    </flags>
>  
> -  <flags id="i386_efer" size="8">
> +  <flags id="i386_efer" size="4">
>       <field name="TCE" start="15" end="15"/>
>       <field name="FFXSR" start="14" end="14"/>
>       <field name="LMSLE" start="13" end="13"/>


-- 
Alex Bennée