Re: [RESEND][PATCH v3 10/17] x86/static_call: Add inline static call implementation for x86-64

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Mar 24, 2020 at 02:56:13PM +0100, Peter Zijlstra wrote:
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> 
> Add the inline static call implementation for x86-64. The generated code
> is identical to the out-of-line case, except we move the trampoline into
> it's own section.
> 
> Then objtool uses the trampoline section to detect all the call sites,
> which it writes into the .static_call_sites section.
> 
> During boot (and module init), the call sites are patched to call
> directly into the destination function.  The temporary trampoline is
> then no longer used.

> +static int read_static_call_tramps(struct objtool_file *file)
> +{
> +	struct section *sec, *sc_sec = find_section_by_name(file->elf, ".static_call.text");
> +	struct symbol *func;
> +
> +	for_each_sec(file, sec) {
> +		list_for_each_entry(func, &sec->symbol_list, list) {
> +			if (func->sec == sc_sec)
> +				func->static_call_tramp = true;
> +		}
> +	}
> +
> +	return 0;
> +}

While talking Boris through this stuff, I just realized that if you use
a static_call object defined in another translation-unit, IOW. the:

	STATIC_CALL_TRAMP(name)(...);

call is an external call, the above objtool rule will not detect it and
it'll stay using the trampoline...

Back to using a naming prefix I suppose.