Re: [PATCH v6 10/17] x86/static_call: Add inline static call implementation for x86-64

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 10, 2020 at 06:31:55PM -0400, Steven Rostedt wrote:
> On Fri, 10 Jul 2020 15:38:41 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:

> > +		/* find key symbol */
> > +		key_name = strdup(insn->call_dest->name);
> 
> Should check for failed allocation of strdup().

Rigt, I'll go add the perror and exit.

> > +		if (strncmp(key_name, STATIC_CALL_TRAMP_PREFIX_STR,
> > +			    strlen(STATIC_CALL_TRAMP_PREFIX_STR))) {
> > +			WARN("static_call: trampoline name malformed: %s", key_name);
> > +			return -1;
> > +		}
> > +		tmp = key_name + STATIC_CALL_TRAMP_PREFIX_LEN - STATIC_CALL_KEY_PREFIX_LEN;
> > +		memcpy(tmp, STATIC_CALL_KEY_PREFIX_STR, STATIC_CALL_KEY_PREFIX_LEN);
> > +
> > +		key_sym = find_symbol_by_name(file->elf, tmp);
> > +		if (!key_sym) {
> > +			WARN("static_call: can't find static_call_key symbol: %s", tmp);
> > +			return -1;
> > +		}
> > +		free(key_name);
> > +
> > +		/* populate reloc for 'key' */
> > +		reloc = malloc(sizeof(*reloc));
> > +		if (!reloc) {
> > +			perror("malloc");
> > +			return -1;
> > +		}
> > +		memset(reloc, 0, sizeof(*reloc));
> > +		reloc->sym = key_sym;
> > +		reloc->addend = 0;
> > +		reloc->type = R_X86_64_PC32;
> 
> How easy would this be for other architectures to implement this? That
> is how much of this function is x86 specific?

I'm not sure; I think it's fairly generic except for the reloc types. So
ARM64 for example might need to use SHT_REL and R_AARCH64_PREL32
instead. But I suppose we'll see that if/when someone tries to make it
work.