Re: [Qemu-devel] [PATCH v6 00/25] Add qemu_getrandom and ARMv8.5-RNG etc

[Richard Henderson]

On 5/14/19 2:43 PM, Eric Blake wrote:
>> It didn't occur to me that there was nothing in the object files for the
>> reference.  I'll have to drop the crypto-obj-y patch and come up with a
>> different solution.
> 
> Isn't there a gcc annotation for marking a simple as mandatorily
> included during link?

No.

There's stuff you can mark a single function within an object file that you can
use to avoid the function being elided...

> __attribute__((externally_visible)) sounds promising (it nullifies the
> effects of -fwhole-program, so that a function remains visible even if
> the linker would have otherwise suppressed it)
> 
> __attribute__((used)) also sounds useful (the function must be emitted
> even if it does not appear to be referenced, which may be enough for the
> linker to infer that it is used)

... and you found those.  But those do not affect the linker's behaviour with
.a files at all.

You can force a symbol reference from the ld command-line: -u sym, which can
cause the .o containing sym to be included from the .a file.  But that doesn't
work if there's no global symbol in the .o to reference.

You can force all .o from a .a file to be included, with --whole-archive.  That
is useful when you're using .a files a shorthand for lots and lots of .o files.
 But in our case that would break the use of stubs.

Anyway, see v7 now.


r~