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

From: "Jan Beulich" <JBeulich@suse.com>
To: Konrad Rzeszutek Wilk <konrad@kernel.org>
Cc: sstabellini@kernel.org, Keir Fraser <keir@xen.org>,
	andrew.cooper3@citrix.com, mpohlack@amazon.com,
	ross.lagerwall@citrix.com, julien.grall@arm.com,
	sasha.levin@oracle.com, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v8.1 11/27] xsplice: Implement payload loading
Date: Thu, 21 Apr 2016 00:41:58 -0600	[thread overview]
Message-ID: <5718925602000078000E434A@prv-mh.provo.novell.com> (raw)
In-Reply-To: <CACJDEmoB3VZBw=5Trv3_9=v-oUhrb=L2ShbEJxdQpoK=TWuxag@mail.gmail.com>

>>> On 20.04.16 at 19:36, <konrad@kernel.org> wrote:
> On Apr 20, 2016 6:05 PM, "Jan Beulich" <jbeulich@suse.com> wrote:
>>
>> >>> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> 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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