Sorry, I didn't see previous replies because the emails went to the spam
folder
for some reason.
I didn't mean to waste anybody's time. Apologies. I replied to your
subsequent points below
and I'll send the diff in a new email.
On Sat, Apr 24, 2021 at 2:24 AM Philip Guenther wrote:
> On Fri, Apr 23, 2021 at 3:13 PM Alessandro Pistocchi <
> apukbusin...@gmail.com> wrote:
>
>> -- Forwarded message -
>> From: Alessandro Pistocchi
>> Date: Fri, Apr 23, 2021 at 1:55 PM
>> Subject: umm_map returns unaligned address?
>> To:
>>
>>
>> Hi all,
>>
>> I am fairly new to openbsd so if this is something obvious that I missed
>> please be understanding.
>>
>> I am adding a syscall to openbsd 6.8. I am working on a raspberry pi.
>>
>> During the syscall I allocate some memory that I want to share between the
>> kernel
>> and the calling process.
>>
>> When it's time to wrap up and unmap the memory, I unmap it both from the
>> kernel
>> map and from the process map.
>>
>> The unmapping from the process map goes fine, the unmapping from the
>> kernel
>> map
>> fails by saying that the virtual address in kernel map is not aligned to
>> the page size
>> ( it's actually 4 bytes off ).
>>
>> What have I missed? I assumed that umm_map would return a page aligned
>> virtual
>> address for the kernel mapping as well.
>>
>> Here is my code for creating the shared memory chunk:
>>
>
> Stop sending summaries and just send diffs that compile: you don't know
> everything that is relevant and keep leaving out stuff that is. I'm the
> third person to say this.
>
>
>>
>>
>> // memory_size is a multiple of page size
>> uvm_object = uao_create(memory_size, 0);
>> if(!uvm_object) return;
>>
>> // TODO(ale): make sure that this memory cannot be swapped out
>>
>> uao_reference(uvm_object)
>> if(uvm_map(kernel_map, (vaddr_t *)&memory, round_page(memory_size),
>> uvm_object,
>>0, 0, UVM_MAPFLAG(PROT_READ | PROT_WRITE, PROT_READ | PROT_WRITE,
>>MAP_INHERIT_SHARED, MADV_NORMAL, 0))) {
>>
>
> The cast of &memory is wrong: it's either unnecessary (if memory is of the
> correct type) or totally broken (if it isn't). Why did you think it was
> unnecessary to show how you declared your variables?
>
You're right.
memory is a void * which is zero at call time, vadd_t an unsigned long. I
believed it was ok since I am expecting to receive the address of the start
of the mapping.
>
> You also fail to show your initialization of 'memory'. If you didn't then
> that's ABSOLUTELY wrong and not in line with the existing uses of uvm_map()
> in the kernel. Please consult the uvm_map(9) manpage for what the incoming
> value means.
>
> ...
>
>> uao_reference(uvm_object);
>> if(uvm_map(&p->p_vmspace->vm_map, &memory_in_proc_space,
>> round_page(memory_size), uvm_object,
>>0, 0, UVM_MAPFLAG(PROT_READ | PROT_WRITE, PROT_READ | PROT_WRITE,
>>MAP_INHERIT_NONE, MADV_NORMAL, 0))) {
>> memory = 0;
>>
>
> This error handling is incomplete, lacking an unmap.
>
Yep, I had noticed that and corrected it in my code. However that should
not be related to the problem I get.
>
>
> Philip Guenther
>
