Re: [Qemu-devel] [PATCH v8] target-ppc: gdbstub allow byte swapping for reading/writing registers

[Alexander Graf <agraf@suse.de>]

On 05.04.14 16:51, Andreas Färber wrote:
> Am 04.04.2014 22:23, schrieb Thomas Falcon:
>> 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 <tlfalcon@linux.vnet.ibm.com>
>> ---
>> Differences for v7:
>>
>> Inlined the register_read() and register_write() wrapper functions
>> ---
>>   target-ppc/cpu-qom.h |   1 +
>>   target-ppc/gdbstub.c | 125 +++++++++++++++++++++++++++++++++++++--------------
>>   2 files changed, 92 insertions(+), 34 deletions(-)
>>
>> diff --git a/target-ppc/cpu-qom.h b/target-ppc/cpu-qom.h
>> index 47dc8e6..aab4977 100644
>> --- a/target-ppc/cpu-qom.h
>> +++ b/target-ppc/cpu-qom.h
>> @@ -111,6 +111,7 @@ void ppc_cpu_dump_state(CPUState *cpu, FILE *f, fprintf_function cpu_fprintf,
>>                           int flags);
>>   void ppc_cpu_dump_statistics(CPUState *cpu, FILE *f,
>>                                fprintf_function cpu_fprintf, int flags);
>> +void ppc_cpu_gdb_swap_register(uint8_t *buf, int reg, int len);
> This is only ever used in gdbstub.c. Can we please keep it static there
> to avoid a full ppc*-softmmu rebuild?
>
>>   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_write_register(CPUState *cpu, uint8_t *buf, int reg);
>> diff --git a/target-ppc/gdbstub.c b/target-ppc/gdbstub.c
>> index 1c91090..594dd08 100644
>> --- a/target-ppc/gdbstub.c
>> +++ b/target-ppc/gdbstub.c
>> @@ -21,6 +21,58 @@
>>   #include "qemu-common.h"
>>   #include "exec/gdbstub.h"
>>   
>> +static int ppc_cpu_gdb_register_len(int n)
> Nitpick: Since these two functions do not operate on the CPU, you could
> just use ppc_gdb_* rather than ppc_cpu_gdb_*.
>
>> +{
>> +    switch (n) {
>> +    case 0 ... 31:
>> +        /* gprs */
>> +        return sizeof(target_ulong);
>> +    case 32 ... 63:
>> +        /* fprs */
>> +        if (gdb_has_xml) {
>> +            return 0;
>> +        }
>> +        return 8;
>> +    case 66:
>> +        /* cr */
>> +        return 4;
>> +    case 64:
>> +        /* nip */
>> +    case 65:
>> +        /* msr */
>> +    case 67:
>> +        /* lr */
>> +    case 68:
>> +        /* ctr */
>> +    case 69:
>> +        /* xer */
>> +        return sizeof(target_ulong);
>> +    case 70:
>> +        /* fpscr */
>> +        if (gdb_has_xml) {
>> +            return 0;
>> +        }
>> +        return sizeof(target_ulong);
>> +    default:
>> +        return 0;
>> +    }
>> +}
>> +
>> +
>> +/* 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
>> + */
>> +
>> +void ppc_cpu_gdb_swap_register(uint8_t *mem_buf, int n, int len)
>> +{
>> +    if (len == 4) {
>> +        bswap32s((uint32_t *)mem_buf);
>> +    } else {
>> +        bswap64s((uint64_t *)mem_buf);
>> +    }
> This logic assumes that len can only be either 4 or 8. Please use an
> explicit len == 8 comparison and g_assert_not_reached() on unhandled len
> values.
>
>> +}
>> +
>>   /* Old gdb always expects FP registers.  Newer (xml-aware) gdb only
>>    * expects whatever the target description contains.  Due to a
>>    * historical mishap the FP registers appear in between core integer
>> @@ -32,23 +84,26 @@ int ppc_cpu_gdb_read_register(CPUState *cs, uint8_t *mem_buf, int n)
>>   {
>>       PowerPCCPU *cpu = POWERPC_CPU(cs);
>>       CPUPPCState *env = &cpu->env;
>> +    int r = ppc_cpu_gdb_register_len(n);
>> +
>> +    if (!r) {
>> +        return r;
>> +    }
>>   
>>       if (n < 32) {
>>           /* gprs */
>> -        return gdb_get_regl(mem_buf, env->gpr[n]);
>> +        gdb_get_regl(mem_buf, env->gpr[n]);
>>       } else if (n < 64) {
>>           /* fprs */
>> -        if (gdb_has_xml) {
>> -            return 0;
>> -        }
> I stumbled over dropping this not being related to Little Endian or
> being mentioned in the commit message. Maybe mention that this is
> replaced by ..._register_len() and returning early?

Just split the patch into 2 separate patches. One to extract the length 
calculation and another one to enable LE.


Alex