Re: [PATCH] kexec/fs2dt: fix endianess conversion

Laurent Dufour
2013-10-16T09:34:10Z

On 16/10/2013 09:28, Simon Horman wrote:
> On Tue, Oct 15, 2013 at 07:05:28PM +0200, Laurent Dufour wrote:
>> While reviewing fs2dt.c in the common kexec directory, in order to use it to
>> support little endian ppc64 architecture, I found some endianess
>> conversion's issues.
>>
>> In dt_reserve, dt_base is a pointer and thus should not be converted.
>>
>> In checkprop, values read from the device tree are big endian encoded and
>> should be converted if CPU is running in little endian mode.
>>
>> In add_dyn_reconf_usable_mem_property__, fix extraneous endianess conversion
>> of rlen which should be natively used to increase the dt pointer.
>
> These changes seem logical to me.
>
> However, I'm unsure how the code might have worked as-is.
> In particular I'm pretty sure ARM was running in little endian
> mode when I worked on DT support for it. Perhaps these code
> paths were not executed. Or the errors cancelled themselves out somehow?

I've to admit that I don't know how this has worked for ARM.
I run this patch with a set of change I'm working on to support PPC64
little endian architecture. My tests were done with kexec-tools built in
little endian mode, using this fs2dt.c file and I need this fix to build
a valid device tree.

The fix is dt_reserve is hit unless the device tree is large enough. I
had to reduce INIT_TREE_WORDS to hit it.

I think the ones in checkprop, add_dyn_reconf_usable_mem_property__ are
Power specific since RTAS and 'ibm,dynamic-memory' are required to hit them.

This may explain why this issue are not seen in ARM mode.

This being said, I wondering if the files fs2dt.c defined in the
arch/ppc64 and arch/ppc directories need to be kept. What do you think
about removing those files and belong on the common kexec/fs2dt.c file
for all the supported architecture ?

Cheers,
Laurent.

>>
>> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
>> ---
>> kexec/fs2dt.c | 19 +++++++++++--------
>> 1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/kexec/fs2dt.c b/kexec/fs2dt.c
>> index 242a15e..5d774ae 100644
>> --- a/kexec/fs2dt.c
>> +++ b/kexec/fs2dt.c
>> @@ -84,7 +84,7 @@ static void dt_reserve(unsigned **dt_ptr, unsigned words)
>> offset = *dt_ptr - dt_base;
>> dt_base = new_dt;
>> dt_cur_size = new_size;
>> - *dt_ptr = cpu_to_be32((unsigned)dt_base + offset);
>> + *dt_ptr = dt_base + offset;
>> memset(*dt_ptr, 0, (new_size - offset)*4);
>> }
>> }
>> @@ -112,19 +112,22 @@ static void checkprop(char *name, unsigned *data, int len)
>> if ((data == NULL) && (base || size || end))
>> die("unrecoverable error: no property data");
>> else if (!strcmp(name, "linux,rtas-base"))
>> - base = *data;
>> + base = be32_to_cpu(*data);
>> else if (!strcmp(name, "linux,tce-base"))
>> - base = *(unsigned long long *) data;
>> + base = be64_to_cpu(*(unsigned long long *) data);
>> else if (!strcmp(name, "rtas-size") ||
>> !strcmp(name, "linux,tce-size"))
>> - size = *data;
>> + size = be32_to_cpu(*data);
>> else if (reuse_initrd && !strcmp(name, "linux,initrd-start"))
>> if (len == 8)
>> - base = *(unsigned long long *) data;
>> + base = be64_to_cpu(*(unsigned long long *) data);
>> else
>> - base = *data;
>> + base = be32_to_cpu(*data);
>> else if (reuse_initrd && !strcmp(name, "linux,initrd-end"))
>> - end = *(unsigned long long *) data;
>> + if (len == 8)
>> + end = be64_to_cpu(*(unsigned long long *) data);
>> + else
>> + end = be32_to_cpu(*data);
>>
>> if (size && end)
>> die("unrecoverable error: size and end set at same time\n");
>> @@ -267,7 +270,7 @@ static void add_dyn_reconf_usable_mem_property__(int fd)
>> pad_structure_block(rlen);
>> memcpy(dt, ranges, rlen);
>> free(ranges);
>> - dt += cpu_to_be32((rlen + 3)/4);
>> + dt += (rlen + 3)/4;
>> }
>>
>> static void add_dyn_reconf_usable_mem_property(struct dirent *dp, int fd)
>>