On 06/21/2018 09:45 PM, Simon Glass wrote:
Hi Alex,
On 21 June 2018 at 03:58, Alexander Graf agraf@suse.de wrote:
On 06/21/2018 04:02 AM, Simon Glass wrote:
Hi Alex,
On 20 June 2018 at 02:51, Alexander Graf agraf@suse.de wrote:
On 06/20/2018 12:02 AM, Simon Glass wrote:
Hi Alex,
On 18 June 2018 at 08:45, Alexander Graf agraf@suse.de wrote:
On 06/18/2018 04:08 PM, Simon Glass wrote: > Use a starting address of 256MB which should be available. This helps > to > make sandbox RAM buffers pointers more recognisable. > > Signed-off-by: Simon Glass sjg@chromium.org
Nak, this has a non-0 chance of failing, in case something else is already mapped at that address. You don't want to have your CI blow up 1% of the time due to this.
It's just a hint though. Everything will still work if it doesn't get this exact address.
I don't see what it buys us then.
These are my thoughts:
- We get an address before 4GB which is needed for grub (so far as I can
tell)
We only need that in the memory map which you want virtual (U-Boot address space) anyway. So there's no need to also have the Linux address be <4GB.
Grub cannot work without <4GB, right? I don't mind either way, but I think it that if we are picking an address, picking a smaller one is better.
Only if you expose host pointers as memory addresses. We don't anymore, and grub doesn't care whether a pointer is >4G.
- It will normally be a nice, easy-on-the-eyes address
I'd rather say it's going to confuse people, because now it's easy to mistake for a U-Boot address.
That's possibly true, although at present it is outside the range of valid U-Boot addresses. What do you suggest?
I see little reason for change. Also if you want to change it, it's out of scope of the efi_loader enablement ;).
- If it isn't, it will hopefully still be an address below 4GB
- Even if not (e.g. on some very strange system) it will still allow
sandbox to start up
But anyway, as I said, this will never fail, it is just a hint. So I think your original comment is incorrect.
It will not fail, it will just potentially not map at exactly the spot you wanted the map at, which IMHO would cause even more confusion.
Imagine people now start to assume that %p output is stable between invocations - because it is 99% of the cases. They start to integrate that into their CI suites and suddenly things fail 1% of the time because the linker figured today's a great day to map glibc at that address.
Remember these are internal sandbox addresses. They should not be visible to most of the code and it is very hard for me to imagine a test that could fail because the address is mapped in different places. How would you access the address from a test? Are you thinking of something that would assume the ram buffer address is something in particular and then call map_to_sysmem() on the pointer? I am really not sure that we should worry about that too much.
No, I'm mostly worried about people assuming that 2 invocations of a U-Boot binary give them the same console output, even when there are printf()s that contain a %p.
Alex