Re: [Xen-devel] [PATCH v8.1 11/27] xsplice: Implement payload loading

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.04.16 at 19:36, <konrad@xxxxxxxxxx> wrote:
> On Apr 20, 2016 6:05 PM, "Jan Beulich" <jbeulich@xxxxxxxx> wrote:
>>
>> >>> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 04/20/16 6:00 PM >>>
>> >> >+ size_t pages; /* Total pages for [text,rw,ro]_addr */
>> >>
>> >> Why size_t and not just unsigned int?
>> >
>> >Oh. I was somehow under the impression you liked size_t more than
>> >unsignged int! I will change it over.
>>
>> When used where actually talking about sizes, I indeed prefer size_t. But
>> here we have a count which we know will be much lower than UINT_MAX.
>>
>> >> >+static void calc_section(struct xsplice_elf_sec *sec, size_t *size)
>> >> >+{
>> >> >+    Elf_Shdr *s = sec->sec;
>> >> >+    size_t align_size;
>> >> >+
>> >> >+    align_size = ROUNDUP(*size, s->sh_addralign);
>> >> >+    s->sh_entsize = align_size;
>> >>
>> >> So this is one of the places (the only one?) where the section header gets
>> >> altered. Are you not expecting problems down the road resulting from
>> >> overwriting this field? After all it's used not just in control 
>> >> sections...
>> >
>> >The 'man elf' tells me :
>> >"Some  sections  hold a table of fixed-sized entries, such as a symbol
>> >table.  For such a section, this member gives the size in bytes for each 
>> >entry.
>> >This member contains zero if the section does not hold  a  table  of
>> >fixed-size entries."
>>
>> My main concern is that SHF_MERGE sections (i.e. ordinary data ones) also
>> already use this field.
> 
> OK. Let me add the 'offset' member (in xsplice_elf_sec) to store the value.
> 
> Albeit it only gets used during move_payload. And later that offset value
> can easily computed using ->load_addr minus ->data.
> 
> Perhaps I should introduce an temporary array to hold this value instead?

Whichever is more feasible / less convoluted, I would say.

Jan


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