On Mon, Jun 01, 2020 at 12:06:34PM -0700, Andrii Nakryiko wrote:

On Sun, May 31, 2020 at 8:10 AM Jiri Olsa [off-list ref] wrote:

quoted

On Fri, May 29, 2020 at 01:48:58PM -0700, Andrii Nakryiko wrote:

quoted

On Thu, May 28, 2020 at 10:24 AM Jiri Olsa [off-list ref] wrote:

quoted

On Thu, May 14, 2020 at 03:46:26PM -0700, Andrii Nakryiko wrote:

SNIP

quoted

quoted

I was thinking of putting the names in __init section and generate the BTF
ids on kernel start, but the build time generation seemed more convenient..
let's see the linking times with 'real size' whitelist and we can reconsider

Being able to record such places where to put BTF ID in code would be
really nice, as Alexei mentioned. There are many potential use cases
where it would be good to have BTF IDs just put into arbitrary
variables/arrays. This would trigger compilation error, if someone
screws up the name, or function is renamed, or if function can be
compiled out under some configuration. E.g., assuming some reasonable
implementation of the macro

hi,
I'm struggling with this part.. to get some reasonable reference
to function/name into 32 bits? any idea? ;-)

Well, you don't have to store actual pointer, right? E.g, emitting
something like this in assembly:

.global __BTF_ID___some_function
.type __BTF_ID___some_function, @object
.size __BTF_ID___some_function, 4
__BTF_ID___some_function:
.zero  4

Would reserve 4 bytes and emit __BTF_ID___some_function symbol. If we
can then post-process vmlinux image and for all symbols starting with
__BTF_ID___ find some_function BTF type id and put it into those 4
bytes, that should work, no?

Maybe generalize it to __BTF_ID__{func,struct,typedef}__some_function,
whatever, not sure. Just an idea.

nice, so something like below?

it'd be in .S file, or perhaps in inline asm, assuming I'll be
able to pass macro arguments to asm("")

I'd do inline asm, there are no arguments you need to pass into
asm("") itself, everything can be done through macro string
interpolation, I think. Having everything in .c file would be way more
convenient and obvious.

wil will do it in inline asm

thanks,
jirka