Re: [PATCH V17 4/6] hw/mips: Add Loongson-3 boot parameter helpers

[Huacai Chen]

Hi, Philippe,

On Mon, Dec 14, 2020 at 9:49 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 12/14/20 3:37 AM, Huacai Chen wrote:
> > Hi, Philippe,
> >
> > On Mon, Dec 14, 2020 at 7:09 AM Philippe Mathieu-Daudé <f4bug@amsat.org> 
> > wrote:
> >>
> >> On 12/13/20 11:17 PM, Philippe Mathieu-Daudé wrote:
> >>> On 12/11/20 12:32 PM, Philippe Mathieu-Daudé wrote:
> >>>> On 12/11/20 3:46 AM, Huacai Chen wrote:
> >>>>> Hi, Rechard and Peter,
> >>>>>
> >>>>> On Wed, Dec 2, 2020 at 5:32 PM Philippe Mathieu-Daudé <f4bug@amsat.org> 
> >>>>> wrote:
> >>>>>>
> >>>>>> On 12/2/20 2:14 AM, Huacai Chen wrote:
> >>>>>>> Hi, Phillippe,
> >>>>>>>
> >>>>>>> On Tue, Nov 24, 2020 at 6:25 AM Philippe Mathieu-Daudé 
> >>>>>>> <f4bug@amsat.org> wrote:
> >>>>>>>>
> >>>>>>>> On 11/6/20 5:21 AM, Huacai Chen wrote:
> >>>>>>>>> Preparing to add Loongson-3 machine support, add Loongson-3's LEFI 
> >>>>>>>>> (a
> >>>>>>>>> UEFI-like interface for BIOS-Kernel boot parameters) helpers first.
> >>>>>>>>>
> >>>>>>>>> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> >>>>>>>>> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> >>>>>>>>> Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> >>>>>>>>> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> >>>>>>>>> ---
> >>>>>>>>>  hw/mips/loongson3_bootp.c | 165 +++++++++++++++++++++++++++++++
> >>>>>>>>>  hw/mips/loongson3_bootp.h | 241 
> >>>>>>>>> ++++++++++++++++++++++++++++++++++++++++++++++
> >>>>>>>>>  hw/mips/meson.build       |   1 +
> >>>>>>>>>  3 files changed, 407 insertions(+)
> >>>>>>>>>  create mode 100644 hw/mips/loongson3_bootp.c
> >>>>>>>>>  create mode 100644 hw/mips/loongson3_bootp.h
> >>>>>>>>>
> >>>>>>>>> diff --git a/hw/mips/loongson3_bootp.c b/hw/mips/loongson3_bootp.c
> >>>>>>>>> new file mode 100644
> >>>>>>>>> index 0000000..3a16081
> >>>>>>>>> --- /dev/null
> >>>>>>>>> +++ b/hw/mips/loongson3_bootp.c
> >>>>>>>>> @@ -0,0 +1,165 @@
> >>>>>>>>> +/*
> >>>>>>>>> + * LEFI (a UEFI-like interface for BIOS-Kernel boot parameters) 
> >>>>>>>>> helpers
> >>>>>>>>> + *
> >>>>>>>>> + * Copyright (c) 2018-2020 Huacai Chen (chenhc@lemote.com)
> >>>>>>>>> + * Copyright (c) 2018-2020 Jiaxun Yang <jiaxun.yang@flygoat.com>
> >>>>>>>>> + *
> >>>>>>>>> + * This program is free software: you can redistribute it and/or 
> >>>>>>>>> modify
> >>>>>>>>> + * it under the terms of the GNU General Public License as 
> >>>>>>>>> published by
> >>>>>>>>> + * the Free Software Foundation, either version 2 of the License, 
> >>>>>>>>> or
> >>>>>>>>> + * (at your option) any later version.
> >>>>>>>>> + *
> >>>>>>>>> + * This program is distributed in the hope that it will be useful,
> >>>>>>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>>>>>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> >>>>>>>>> + * GNU General Public License for more details.
> >>>>>>>>> + *
> >>>>>>>>> + * You should have received a copy of the GNU General Public 
> >>>>>>>>> License
> >>>>>>>>> + * along with this program. If not, see 
> >>>>>>>>> <https://www.gnu.org/licenses/>.
> >>>>>>>>> + */
> >>>>>>>>> +
> >>>>>>>>> +#include "qemu/osdep.h"
> >>>>>>>>> +#include "qemu/units.h"
> >>>>>>>>> +#include "qemu/cutils.h"
> >>>>>>>>> +#include "cpu.h"
> >>>>>>>>> +#include "hw/boards.h"
> >>>>>>>>> +#include "hw/mips/loongson3_bootp.h"
> >>>>>>>>> +
> >>>>>>>>> +#define LOONGSON3_CORE_PER_NODE 4
> >>>>>>>>> +
> >>>>>>>>> +static struct efi_cpuinfo_loongson *init_cpu_info(void *g_cpuinfo, 
> >>>>>>>>> uint64_t cpu_freq)
> >>>>>>>>> +{
> >>>>>>>>> +    struct efi_cpuinfo_loongson *c = g_cpuinfo;
> >>>>>>>>> +
> >>>>>>>>> +    stl_le_p(&c->cputype, Loongson_3A);
> >>>>>>>>> +    stl_le_p(&c->processor_id, MIPS_CPU(first_cpu)->env.CP0_PRid);
> >>>>>>>>
> >>>>>>>> Build failing with Clang:
> >>>>>>>>
> >>>>>>>> FAILED: libqemu-mips64el-softmmu.fa.p/hw_mips_loongson3_bootp.c.o
> >>>>>>>> hw/mips/loongson3_bootp.c:35:15: error: taking address of packed 
> >>>>>>>> member
> >>>>>>>> 'processor_id' of class or structure 'efi_cpuinfo_loongson' may 
> >>>>>>>> result
> >>>>>>>> in an unaligned pointer value [-Werror,-Waddress-of-packed-member]
> >>>>>>>>     stl_le_p(&c->processor_id, MIPS_CPU(first_cpu)->env.CP0_PRid);
> >>>>>>>>               ^~~~~~~~~~~~~~~
> >>>>>>>> 1 error generated.
> >>>>>>> We cannot reproduce it on X86/MIPS with clang...
> >>>>>>
> >>>>>> You can reproduce running the Clang job on Gitlab-CI:
> >>>>>>
> >>>>>> https://wiki.qemu.org/Testing/CI/GitLabCI
> >>>>>>
> >>>>>>> And I found that
> >>>>>>> stl_le_p() will be __builtin_memcpy(), I don't think memcpy() will
> >>>>>>> cause unaligned access. So, any suggestions?
> >>>>
> >>>> My understanding is the compiler is complaining for the argument
> >>>> passed to the caller, with no knowledge of the callee implementation.
> >>>>
> >>>> Which makes me wonder if these functions are really inlined...
> >>>>
> >>>> Do we need to use QEMU_ALWAYS_INLINE for these LDST helpers?
> >>>
> >>> No, this doesn't work neither.
> >>
> >> Well, this works:
> >>
> >> -- >8 --
> >> @@ -32,7 +32,7 @@ static struct efi_cpuinfo_loongson *init_cpu_info(void
> >> *g_cpuinfo, uint64_t cpu_
> >>      struct efi_cpuinfo_loongson *c = g_cpuinfo;
> >>
> >>      stl_le_p(&c->cputype, Loongson_3A);
> >> -    stl_le_p(&c->processor_id, MIPS_CPU(first_cpu)->env.CP0_PRid);
> >> +    c->processor_id = cpu_to_le32(MIPS_CPU(first_cpu)->env.CP0_PRid);
> >>      if (cpu_freq > UINT_MAX) {
> >>          stl_le_p(&c->cpu_clock_freq, UINT_MAX);
> >>      } else {
> >
> > This seems not allowed. In include/qemu/bswap.h it says:
> >  * Do an in-place conversion of the value pointed to by @v from the
> >  * native endianness of the host CPU to the specified format.
> >  *
> >  * Both X_to_cpu() and cpu_to_X() perform the same operation; you
> >  * should use whichever one is better documenting of the function your
> >  * code is performing.
> >  *
> >  * Do not use these functions for conversion of values which are in guest
> >  * memory, since the data may not be sufficiently aligned for the host CPU's
> >  * load and store instructions. Instead you should use the ld*_p() and
> >  * st*_p() functions, which perform loads and stores of data of any
> >  * required size and endianness and handle possible misalignment.
> >
> > And there is a very strange problem, nearly all 32bit members are
> > after a 16bit vers member, why only processor_id is special? Compiler
> > bug?
>
> This is what I wonder since some time but I don't have the knowledge
> to confirm.
>
> Indeed I commented the "stl_le_p(&c->processor_id, ...);" line,
> and there is no error for the following 32-bit values, which are
> similarly unlikely 32-bit aligned.
>
> FWIW I am using Fedora release 32 (Thirty Two), and 'cc -v':
>
>  clang version 10.0.1 (Fedora 10.0.1-3.fc32)
>  Target: x86_64-unknown-linux-gnu
>  clang -cc1 version 10.0.1 based upon LLVM 10.0.1 default target
> x86_64-unknown-linux-gnu
>
Since cpu_to_le32() "solve" the problem here, I want to use
cpu_to_lexx() for all members, do you agree?

Huacai

> >
> > Huacai
> >> ---
> >>
> >>>
> >>>>
> >>>> I see Richard used it in commit 80d9d1c6785 ("cputlb: Split out
> >>>> load/store_memop").
> >>>>
> >>>>>>
> >>>>>> I'll defer this question to Richard/Peter who have deeper 
> >>>>>> understanding.
> >>>>> Any sugguestions? Other patches are updated, except this one.
> >>>>
> >>>> Searching on the list, I see Marc-André resolved that by
> >>>> using a copy on the stack:
> >>>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg614482.html