On Fri, Nov 09, 2018 at 10:51:16AM +0100, Ard Biesheuvel wrote: > Hi Josh, > > Thanks a lot for looking into this. > > On 8 November 2018 at 22:15, Josh Poimboeuf <[email protected]> wrote: > > Add a static call infrastructure. Static calls use code patching to > > hard-code function pointers into direct branch instructions. They give > > the flexibility of function pointers, but with improved performance. > > This is especially important for cases where retpolines would otherwise > > be used, as retpolines can significantly impact performance. > > > > This code is heavily inspired by the jump label code (aka "static > > jumps"), as some of the concepts are very similar. > > > > There are three implementations, depending on arch support: > > > > 1) optimized: patched call sites (CONFIG_HAVE_STATIC_CALL_OPTIMIZED) > > 2) unoptimized: patched trampolines (CONFIG_HAVE_STATIC_CALL_UNOPTIMIZED) > > Could we move to an idiom like inline/out of line? The unoptimized > variant may be perfectly adequate for many arches, and 'unoptimized' > sounds like there is something wrong with it.
Yeah, inline/out-of-line would be better. It's both more descriptive and less derogatory :-) > > + * Usage example: > > + * > > + * # Start with the following functions (with identical prototypes): > > + * int func_a(int arg1, int arg2); > > + * int func_b(int arg1, int arg2); > > + * > > + * # Define a 'my_key' reference, associated with func_a() by default > > + * DEFINE_STATIC_CALL(my_key, func_a); > > + * > > + * # Call func_a() > > + * static_call(my_key, arg1, arg2); > > + * > > + * # Update 'my_key' to point to func_b() > > + * static_call_update(my_key, func_b); > > + * > > + * # Call func_b() > > + * static_call(my_key, arg1, arg2); > > + * > > Any way we can revert to the default implementation? That would be > useful for, e.g., unloading modules that provide an alternative > implementation. I saw your original implementation had a "reset to default", but from what I can tell, most users wouldn't need that. Assuming the caller knows what the original dest function was, can't they just call static_call_update(my_key, orig_func) directly? > > diff --git a/include/linux/static_call_types.h > > b/include/linux/static_call_types.h > > new file mode 100644 > > index 000000000000..7dd4b3d7ec2b > > --- /dev/null > > +++ b/include/linux/static_call_types.h > > @@ -0,0 +1,19 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +#ifndef _STATIC_CALL_TYPES_H > > +#define _STATIC_CALL_TYPES_H > > + > > +#include <linux/stringify.h> > > + > > +#define STATIC_CALL_TRAMP_PREFIX ____static_call_tramp_ > > +#define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX) > > + > > +#define STATIC_CALL_TRAMP(key) STATIC_CALL_TRAMP_PREFIX##key > > +#define STATIC_CALL_TRAMP_STR(key) __stringify(STATIC_CALL_TRAMP(key)) > > + > > I needed to apply > > diff --git a/include/linux/static_call_types.h > b/include/linux/static_call_types.h > index 7dd4b3d7ec2b..6859b208de6e 100644 > --- a/include/linux/static_call_types.h > +++ b/include/linux/static_call_types.h > @@ -7,7 +7,7 @@ > #define STATIC_CALL_TRAMP_PREFIX ____static_call_tramp_ > #define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX) > > -#define STATIC_CALL_TRAMP(key) STATIC_CALL_TRAMP_PREFIX##key > +#define STATIC_CALL_TRAMP(key) __PASTE(STATIC_CALL_TRAMP_PREFIX, key) > #define STATIC_CALL_TRAMP_STR(key) __stringify(STATIC_CALL_TRAMP(key)) > > /* The static call site table is created by objtool. */ > > or I end up with > > 0000000000000000 <STATIC_CALL_TRAMP_PREFIXfoo>: > 0: 14000000 b a8 <foo_a> > 4: d503201f nop Ha, oops. That was part of a last minute cleanup to share the macros with objtool. -- Josh
