linux-kernel - Re: [PATCH 06/17] coresight: tmc: Make ETR SG table circular

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Date:   Thu, 9 Nov 2017 09:19:15 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        rob.walker@....com, Mike Leach <mike.leach@...aro.org>,
        coresight@...ts.linaro.org
Subject: Re: [PATCH 06/17] coresight: tmc: Make ETR SG table circular

On 7 November 2017 at 03:36, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
> On 06/11/17 19:07, Mathieu Poirier wrote:
>>
>> On Thu, Oct 19, 2017 at 06:15:42PM +0100, Suzuki K Poulose wrote:
>
>
> ...
>
>>> +/*
>>> + * tmc_etr_sg_offset_to_table_index : Translate a given data @offset
>>> + * to the index of the page table "entry". Data pointers always have
>>> + * a fixed location, with ETR_SG_PTRS_PER_PAGE - 1 entries in an
>>> + * ETR_SG_PAGE and 1 link entry per (ETR_SG_PTRS_PER_PAGE -1) entries.
>>> + */
>>> +static inline u32
>>> +tmc_etr_sg_offset_to_table_index(u64 offset)
>>> +{
>>> +       u64 sgpage_idx = offset >> ETR_SG_PAGE_SHIFT;
>>> +
>>> +       return sgpage_idx + sgpage_idx / (ETR_SG_PTRS_PER_PAGE - 1);
>>> +}
>>
>>
>> This function is the source of a bizarre linking error when compiling
>> [14/17] on
>> armv7 as pasted here:
>>
>>    UPD     include/generated/compile.h
>>    CC      init/version.o
>>    AR      init/built-in.o
>>    AR      built-in.o
>>    LD      vmlinux.o
>>    MODPOST vmlinux.o
>> drivers/hwtracing/coresight/coresight-tmc-etr.o: In function
>> `tmc_etr_sg_offset_to_table_index':
>>
>> /home/mpoirier/work/linaro/coresight/kernel-maint/drivers/hwtracing/coresight/coresight-tmc-etr.c:553:
>> undefined reference to `__aeabi_uldivmod'
>>
>> /home/mpoirier/work/linaro/coresight/kernel-maint/drivers/hwtracing/coresight/coresight-tmc-etr.c:551:
>> undefined reference to `__aeabi_uldivmod'
>>
>> /home/mpoirier/work/linaro/coresight/kernel-maint/drivers/hwtracing/coresight/coresight-tmc-etr.c:553:
>> undefined reference to `__aeabi_uldivmod'
>> drivers/hwtracing/coresight/coresight-tmc-etr.o: In function
>> `tmc_etr_sg_table_rotate':
>>
>> /home/mpoirier/work/linaro/coresight/kernel-maint/drivers/hwtracing/coresight/coresight-tmc-etr.c:609:
>> undefined reference to `__aeabi_uldivmod'
>>
>> Please see if you can reproduce on your side.
>
>
> Uh ! I had gcc-7, which didn't complain about it. But if switch to 4.9, it
> does.
> It looks like division of 64bit entity on arm32 is triggering it. We don't
> need
> this to be u64 above, as it is the page_idx and could simply switch to
> "unsigned long"
> rather than explicitly using div64 helpers.
>
> The following change fixes the issue for me. Please could you check if it
> solves the problem
> for you ?

Unfortunately it doesn't.

Mathieu

>
>
> @@ -551,7 +553,7 @@ static void tmc_etr_sg_table_populate(struct
> etr_sg_table *etr_table)
>  static inline u32
>  tmc_etr_sg_offset_to_table_index(u64 offset)
>  {
> -       u64 sgpage_idx = offset >> ETR_SG_PAGE_SHIFT;
> +       unsigned long sgpage_idx = offset >> ETR_SG_PAGE_SHIFT;
>          return sgpage_idx + sgpage_idx / (ETR_SG_PTRS_PER_PAGE - 1);
>  }
>
>
>
> Thanks for the testing !
>
> Suzuki