Re: [Qemu-devel] [PATCH v2] target-ppc: gdbstub allow byte swapping for reading/writing registers

[Thomas Falcon]

On 01/16/2014 11:10 AM, Alexander Graf wrote:
> On 16.01.2014, at 17:59, Thomas Falcon <address@hidden> wrote:
>
> > This patch allows registers to be properly read from and written to
> > when using the gdbstub to debug a ppc guest running in little
> > endian mode.  It accomplishes this goal by byte swapping the values of
> > any registers if the MSR:LE value is set.
> >
> > Signed-off-by: Thomas Falcon<address@hidden>
> > ---
> > Have created wrapper functions that swap mem_buf in-place.
> > mem_buf is swapped regardless of the the host's endianness if msr_le is true.
> > ---
> > target-ppc/cpu-qom.h        |  2 ++
> > target-ppc/gdbstub.c        | 48 +++++++++++++++++++++++++++++++++++++++++++++
> > target-ppc/translate_init.c |  4 ++--
> > 3 files changed, 52 insertions(+), 2 deletions(-)
> >
> > diff --git a/target-ppc/cpu-qom.h b/target-ppc/cpu-qom.h
> > index 72b2232..992963f 100644
> > --- a/target-ppc/cpu-qom.h
> > +++ b/target-ppc/cpu-qom.h
> > @@ -109,7 +109,9 @@ void ppc_cpu_dump_statistics(CPUState *cpu, FILE *f,
> >                               fprintf_function cpu_fprintf, int flags);
> > hwaddr ppc_cpu_get_phys_page_debug(CPUState *cpu, vaddr addr);
> > int ppc_cpu_gdb_read_register(CPUState *cpu, uint8_t *buf, int reg);
> > +int ppc_cpu_gdb_read_register_wrap(CPUState *cpu, uint8_t *buf, int reg);
> > int ppc_cpu_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg);
> > +int ppc_cpu_gdb_write_register_wrap(CPUState *cpu, uint8_t *buf, int reg);
> > int ppc64_cpu_write_elf64_qemunote(WriteCoreDumpFunction f,
> >                                     CPUState *cpu, void *opaque);
> > int ppc64_cpu_write_elf64_note(WriteCoreDumpFunction f, CPUState *cs,
> > diff --git a/target-ppc/gdbstub.c b/target-ppc/gdbstub.c
> > index 1c91090..964fd85 100644
> > --- a/target-ppc/gdbstub.c
> > +++ b/target-ppc/gdbstub.c
> > @@ -21,6 +21,54 @@
> > #include "qemu-common.h"
> > #include "exec/gdbstub.h"
> >
> > +/* The following functions are used to ensure the correct
> > + * transfer of registers between a little endian ppc target
> > + * and a big endian host by checking the LE bit in the Machine State Register
> > + */
> > +
> > +int ppc_cpu_gdb_read_register_wrap(CPUState *cs, uint8_t *mem_buf, int n)
> > +{
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +    CPUPPCState *env = &cpu->env;
> > +
> > +    int len = ppc_cpu_gdb_read_register(cs, mem_buf, n),i;
> > +    if(msr_le)
> > +    {
> > +        uint8_t tmp;
> > +        for(i=0;i<len/2;i++)
> > +        {
> > +            tmp=*(mem_buf+i);
> > +            *(mem_buf+i)=*(mem_buf+len-1-i);
> > +            *(mem_buf+len-1-i)=tmp;
> > +        }
> > +    }
> > +    return len;
> > +}
> > +
> > +int ppc_cpu_gdb_write_register_wrap(CPUState *cs, uint8_t *mem_buf, int n)
> > +{
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +    CPUPPCState *env = &cpu->env;
> > +    if(msr_le)
> > +    {
> > +        int len=0,i=0;
> > +   /     if(n < 64)
> > +            len=8;
> > +        else if(n == 66)
> > +            len=4;
> > +        else
> > +            len = sizeof(target_ulong);
> > +        uint8_t tmp;
> > +        for(i=0;i<len/2;i++)
> > +        {
> > +            tmp=*(mem_buf+i);
> > +            *(mem_buf+i)=*(mem_buf+len-1-i);
> > +            *(mem_buf+len-1-i)=tmp;
> > +        }
> > +    }
> > +    return ppc_cpu_gdb_write_register(cs, mem_buf, n);
> Please run checkpatch.pl :).
>
> Also the return value is already then length. No need to duplicate that logic.
>
>
> Alex
Sorry about the formatting issues.  It slipped my mind.  But what do you mean 
about the return value?

Would you rather this:

ppc_cpu_gdb_write_register(cs, mem_buf, n);
return len;

Thanks for your suggestions,

Tom