On Mon, Jan 15, 2024 at 03:34:05PM +0100, Jan Beulich wrote: > Recent gas versions generate minimalistic Dwarf debug info for items > annotated as functions and having their sizes specified [1]. Furthermore > generating live patches wants items properly annotated. "Borrow" Arm's > END() and (remotely) derive other annotation infrastructure from > Linux'es, for all architectures to use. > > Signed-off-by: Jan Beulich <[email protected]> > > [1] > https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=591cc9fbbfd6d51131c0f1d4a92e7893edcc7a28 > --- > v5: Drop CODE_ALIGN fallback. s/algn/align/g. > v3: New, generalized from earlier x86-only version. LAST() (now > LASTARG()) moved to macros.h. > --- > TBD: {CODE,DATA}_ALIGN are byte granular, such that a value of 0 can be > specified (in case this has some special meaning on an arch; > conceivably it could mean to use some kind of arch default). We may > not strictly need that, and hence we could also make these power- > of-2 values (using .p2align). > > Note that we can't use ALIGN() (in place of SYM_ALIGN()) as long as we > still have ALIGN. > > Note further that FUNC()'s etc "align" parameter is intended to allow > for only no or a single argument. If we wanted to also make the fill > value customizable per call site, the constructs would need re-doing to > some degree. > > --- /dev/null > +++ b/xen/include/xen/linkage.h > @@ -0,0 +1,54 @@ > +#ifndef __LINKAGE_H__ > +#define __LINKAGE_H__ > + > +#ifdef __ASSEMBLY__ > + > +#include <xen/macros.h> > + > +/* CODE_ALIGN needs to be specified by every architecture. */ > +#ifndef CODE_FILL > +# define CODE_FILL ~0 > +#endif > + > +#ifndef DATA_ALIGN > +# define DATA_ALIGN 0 > +#endif > +#ifndef DATA_FILL > +# define DATA_FILL ~0 > +#endif > + > +#define SYM_ALIGN(align...) .balign align > + > +#define SYM_L_GLOBAL(name) .globl name > +#define SYM_L_WEAK(name) .weak name > +#define SYM_L_LOCAL(name) /* nothing */ > + > +#define SYM_T_FUNC STT_FUNC > +#define SYM_T_DATA STT_OBJECT > +#define SYM_T_NONE STT_NOTYPE > + > +#define SYM(name, typ, linkage, align...) \ > + .type name, SYM_T_ ## typ; \ > + SYM_L_ ## linkage(name); \ > + SYM_ALIGN(align); \ > + name: > + > +#define END(name) .size name, . - name > + > +#define FUNC(name, align...) \ > + SYM(name, FUNC, GLOBAL, LASTARG(CODE_ALIGN, ## align), CODE_FILL) > +#define LABEL(name, align...) \ > + SYM(name, NONE, GLOBAL, LASTARG(CODE_ALIGN, ## align), CODE_FILL) > +#define DATA(name, align...) \ > + SYM(name, DATA, GLOBAL, LASTARG(DATA_ALIGN, ## align), DATA_FILL) > + > +#define FUNC_LOCAL(name, align...) \ > + SYM(name, FUNC, LOCAL, LASTARG(CODE_ALIGN, ## align), CODE_FILL) > +#define LABEL_LOCAL(name, align...) \ > + SYM(name, NONE, LOCAL, LASTARG(CODE_ALIGN, ## align), CODE_FILL)
One thing that I've noticed while reviewing further patches, the usage of CODE_ALIGN and CODE_FILL in LABEL_LOCAL() means that CODE_FILL must always be a nop, or else the assembler will put garbage while padding the symbol, and hence the preceding code will no longer fallthrough into the label? Looking further, LABEL_LOCAL() is always used when there's no fallthrough, but it's IMO not obvious from the description here. Thanks, Roger.
