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

Simon Horman
2013-10-17T01:43:23Z

On Wed, Oct 16, 2013 at 11:33:43AM +0200, Laurent Dufour wrote:
> 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.

Perhaps, its a bit of a mystery.
I think that I will apply your change as it does seem to be correct.

>
> 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 ?

I haven't examined the details but that sounds like a good idea to me.

>
> 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)
> >>
> >