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Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks
From: |
Alexey Kardashevskiy |
Subject: |
Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs |
Date: |
Tue, 29 Jan 2019 11:28:01 +1100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
On 29/01/2019 07:00, Fabiano Rosas wrote:
> David Gibson <address@hidden> writes:
>
>> On Thu, Jan 24, 2019 at 06:20:02PM +1100, Alexey Kardashevskiy wrote:
>>>
>>>
>>> On 23/01/2019 04:01, Fabiano Rosas wrote:
>>>> These will be used to let GDB know about PPC's Special Purpose
>>>> Registers (SPR).
>>>>
>>>> They take an index based on the order the registers appear in the XML
>>>> file sent by QEMU to GDB. This index does not match the actual
>>>> location of the registers in the env->spr array so the
>>>> gdb_find_spr_idx function does that conversion.
>>>>
>>>> Signed-off-by: Fabiano Rosas <address@hidden>
>>>> ---
>>>> target/ppc/translate_init.inc.c | 54 ++++++++++++++++++++++++++++++++-
>>>> 1 file changed, 53 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/target/ppc/translate_init.inc.c
>>>> b/target/ppc/translate_init.inc.c
>>>> index 710064a25d..f29ac3558a 100644
>>>> --- a/target/ppc/translate_init.inc.c
>>>> +++ b/target/ppc/translate_init.inc.c
>>>> @@ -9487,6 +9487,55 @@ static bool avr_need_swap(CPUPPCState *env)
>>>> #endif
>>>> }
>>>>
>>>> +#if !defined(CONFIG_USER_ONLY)
>>>> +static int gdb_find_spr_idx(CPUPPCState *env, int n)
>>>> +{
>>>> + int i;
>>>> +
>>>> + for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
>>>> + ppc_spr_t *spr = &env->spr_cb[i];
>>>> +
>>>> + if (spr->name && spr->gdb_id == n) {
>>>> + return i;
>>>> + }
>>>> + }
>>>> + return -1;
>>>> +}
>>>> +
>>>> +static int gdb_get_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
>>>> +{
>>>> + int reg;
>>>> + int len;
>>>> +
>>>> + reg = gdb_find_spr_idx(env, n);
>>>> + if (reg < 0) {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + len = TARGET_LONG_SIZE;
>>>> + stn_p(mem_buf, len, env->spr[reg]);
>>>> + ppc_maybe_bswap_register(env, mem_buf, len);
>>>
>>>
>>> I am confused by this as it produces different results depending on the
>>> guest mode:
>>
>>
>> Hm, yeah, I thought the bswap here looked odd, but it wasn't obvious
>> to me if it was bogus here, or just a bogus gdb interface we have to
>> work around.
>>
>>> (gdb) p $pvr
>>> $1 = 0x14c0000000000
>>> (gdb) c
>>> Continuing.
>>> Program received signal SIGINT, Interrupt.
>>> (gdb) p $pvr
>>> $2 = 0x4c0100
>>
>> But that behaviour definitely looks wrong.
>
> GDB detects the endianness by looking at the ELF headers:
but this is a register which does not have endianness, the endianness
appears here because the interface between gdb and qemu is
uint8_t*==bytestream but this interface should have fixed endianness
imho (now it is bigendian afaict).
Something is not right here...
>
> (gdb) p/x $pvr
> $1 = 0x1024b0000000000
> (gdb) file ~/qemu/roms/SLOF/board-qemu/llfw/stage1.elf
> Reading symbols from ~/qemu/roms/SLOF/board-qemu/llfw/stage1.elf...done.
> (gdb) show endian
> The target endianness is set automatically (currently big endian)
> (gdb) p/x $pvr
> $2 = 0x4b0201
> (gdb) c
> Continuing.
>
> (gdb) ^C
> Program received signal SIGINT, Interrupt.
> 0x74a70c00000000c0 in ?? ()
> (gdb) file vmlinux
> Reading symbols from vmlinux...done.
> (gdb) show endian
> The target endianness is set automatically (currently little endian)
> (gdb) p/x $pvr
> $3 = 0x4b0201
>
> The maybe_bswap_register is done due to QEMU having TARGET_WORDS_BIGENDIAN set
> even after we have changed into LE mode.
>
>>> First print is when I stopped the guest in the SLOF firmware (so it is
>>> big-endian) and then I continued and stopped gdb when the guest booted a
>>> little-endian system; the KVM host is little endian, the machine running
>>> gdb is LE too.
>>>
>>> QEMU monitor prints the same 0x4c0100 in both cases.
>>>
>>> I am adding the inventor of maybe_bswap_register() in cc: for
>>> assistance. Swapping happens:
>>> - once for BE: after stn_p()
>>> *(unsigned long *)mem_buf is 0x14c0000000000
>>> - twice for LE.
>>>
>>>
>>>
>>>
>>>
>>>> + return len;
>>>> +}
>>>> +
>>>> +static int gdb_set_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
>>>> +{
>>>> + int reg;
>>>> + int len;
>>>> +
>>>> + reg = gdb_find_spr_idx(env, n);
>>>> + if (reg < 0) {
>>>> + return 0;
>>>> + }
>>>> +
>>>> + len = TARGET_LONG_SIZE;
>>>> + ppc_maybe_bswap_register(env, mem_buf, len);
>>>> + env->spr[reg] = ldn_p(mem_buf, len);
>>>> +
>>>> + return len;
>>>> +}
>>>> +#endif
>>>> +
>>>> static int gdb_get_float_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
>>>> {
>>>> if (n < 32) {
>>>> @@ -9716,7 +9765,10 @@ static void ppc_cpu_realize(DeviceState *dev, Error
>>>> **errp)
>>>> gdb_register_coprocessor(cs, gdb_get_vsx_reg, gdb_set_vsx_reg,
>>>> 32, "power-vsx.xml", 0);
>>>> }
>>>> -
>>>> +#ifndef CONFIG_USER_ONLY
>>>> + gdb_register_coprocessor(cs, gdb_get_spr_reg, gdb_set_spr_reg,
>>>> + pcc->gdb_num_sprs, "power-spr.xml", 0);
>>>> +#endif
>>>> qemu_init_vcpu(cs);
>>>>
>>>> pcc->parent_realize(dev, errp);
>>>>
>>>
>
--
Alexey
- [Qemu-devel] [PATCH v4 0/3] ppc/gdbstub: Expose SPRs to GDB, Fabiano Rosas, 2019/01/22
- [Qemu-devel] [PATCH v4 1/3] target/ppc: Add SPRs XML generation code for gdbstub, Fabiano Rosas, 2019/01/22
- [Qemu-devel] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Fabiano Rosas, 2019/01/22
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Alexey Kardashevskiy, 2019/01/24
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, David Gibson, 2019/01/26
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Fabiano Rosas, 2019/01/28
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs,
Alexey Kardashevskiy <=
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Fabiano Rosas, 2019/01/30
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Alexey Kardashevskiy, 2019/01/31
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Fabiano Rosas, 2019/01/31
- Re: [Qemu-devel] [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs, Alexey Kardashevskiy, 2019/01/31
[Qemu-devel] [PATCH v4 3/3] target/ppc: Enable reporting of SPRs to GDB, Fabiano Rosas, 2019/01/22