| Message ID | 20240201103339.549307-1-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen/bitmap: Consistently use unsigned bits values | expand |
On 01.02.2024 11:33, Andrew Cooper wrote: > Right now, most of the static inline helpers take an unsigned nbits quantity, > and most of the library functions take a signed quanity. Because > BITMAP_LAST_WORD_MASK() is expressed as a divide, the compiler is forced to > emit two different paths to get the correct semantics for signed division. > > Swap all signed bit-counts to being unsigned bit-counts for the simple cases. > This includes the return value of bitmap_weight(). > > Bloat-o-meter for a random x86 build reports: > add/remove: 0/0 grow/shrink: 8/19 up/down: 167/-413 (-246) > > which all comes from compiler not emitting "dead" logic paths for negative bit > counts. > > No functional change. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> albeit with a question at the bottom. > There is much more wanting cleaning up here, but we have to start somewhere. > Some observations: > > * Various of the boolean-like return values have -1 for zero-length bitmaps. > I can't spot any callers which care, so this seems like a waste. > * bitmap_zero() and similar clear predate us switching to use > __builtin_memset(), because there's no need for bitmap_switch(). > * Should we consolidate 'bits' vs 'nbits'? This looks desirable to me. > * The internals of these helpers want converting too. Other helpers need > more than just a parameter conversion. This may or may not relate to my question; it's not exactly clear what you mean here. > --- a/xen/include/xen/bitmap.h > +++ b/xen/include/xen/bitmap.h > @@ -66,25 +66,25 @@ > * lib/bitmap.c provides these functions: > */ > > -extern int __bitmap_empty(const unsigned long *bitmap, int bits); > -extern int __bitmap_full(const unsigned long *bitmap, int bits); > -extern int __bitmap_equal(const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern void __bitmap_complement(unsigned long *dst, const unsigned long *src, > - int bits); > -extern void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern int __bitmap_intersects(const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern int __bitmap_subset(const unsigned long *bitmap1, > - const unsigned long *bitmap2, int bits); > -extern int __bitmap_weight(const unsigned long *bitmap, int bits); > +int __bitmap_empty(const unsigned long *bitmap, unsigned int bits); > +int __bitmap_full(const unsigned long *bitmap, unsigned int bits); > +int __bitmap_equal(const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +void __bitmap_complement(unsigned long *dst, const unsigned long *src, > + unsigned int bits); > +void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +int __bitmap_intersects(const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +int __bitmap_subset(const unsigned long *bitmap1, > + const unsigned long *bitmap2, unsigned int bits); > +unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int bits); > extern void __bitmap_set(unsigned long *map, unsigned int start, int len); > extern void __bitmap_clear(unsigned long *map, unsigned int start, int len); What about these two, and the subsequent (in the .c file at least) bitmap_*_region()? That last remark above may mean you deliberately left them out for now (which is okay - as you say, this is merely a 1st step). Jan
On 01/02/2024 10:45 am, Jan Beulich wrote: > On 01.02.2024 11:33, Andrew Cooper wrote: >> Right now, most of the static inline helpers take an unsigned nbits quantity, >> and most of the library functions take a signed quanity. Because >> BITMAP_LAST_WORD_MASK() is expressed as a divide, the compiler is forced to >> emit two different paths to get the correct semantics for signed division. >> >> Swap all signed bit-counts to being unsigned bit-counts for the simple cases. >> This includes the return value of bitmap_weight(). >> >> Bloat-o-meter for a random x86 build reports: >> add/remove: 0/0 grow/shrink: 8/19 up/down: 167/-413 (-246) >> >> which all comes from compiler not emitting "dead" logic paths for negative bit >> counts. >> >> No functional change. >> >> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> > Reviewed-by: Jan Beulich <jbeulich@suse.com> Thanks. > albeit with a question at the bottom. > >> There is much more wanting cleaning up here, but we have to start somewhere. >> Some observations: >> >> * Various of the boolean-like return values have -1 for zero-length bitmaps. >> I can't spot any callers which care, so this seems like a waste. >> * bitmap_zero() and similar clear predate us switching to use >> __builtin_memset(), because there's no need for bitmap_switch(). >> * Should we consolidate 'bits' vs 'nbits'? > This looks desirable to me. > >> * The internals of these helpers want converting too. Other helpers need >> more than just a parameter conversion. > This may or may not relate to my question; it's not exactly clear what you > mean here. > >> --- a/xen/include/xen/bitmap.h >> +++ b/xen/include/xen/bitmap.h >> @@ -66,25 +66,25 @@ >> * lib/bitmap.c provides these functions: >> */ >> >> -extern int __bitmap_empty(const unsigned long *bitmap, int bits); >> -extern int __bitmap_full(const unsigned long *bitmap, int bits); >> -extern int __bitmap_equal(const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern void __bitmap_complement(unsigned long *dst, const unsigned long *src, >> - int bits); >> -extern void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern int __bitmap_intersects(const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern int __bitmap_subset(const unsigned long *bitmap1, >> - const unsigned long *bitmap2, int bits); >> -extern int __bitmap_weight(const unsigned long *bitmap, int bits); >> +int __bitmap_empty(const unsigned long *bitmap, unsigned int bits); >> +int __bitmap_full(const unsigned long *bitmap, unsigned int bits); >> +int __bitmap_equal(const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +void __bitmap_complement(unsigned long *dst, const unsigned long *src, >> + unsigned int bits); >> +void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +int __bitmap_intersects(const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +int __bitmap_subset(const unsigned long *bitmap1, >> + const unsigned long *bitmap2, unsigned int bits); >> +unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int bits); >> extern void __bitmap_set(unsigned long *map, unsigned int start, int len); >> extern void __bitmap_clear(unsigned long *map, unsigned int start, int len); > What about these two, and the subsequent (in the .c file at least) > bitmap_*_region()? That last remark above may mean you deliberately > left them out for now (which is okay - as you say, this is merely a > 1st step). They want map->bitmap and int len -> unsigned int bits for consistency, which is more than just a typechange. I also wasn't totally certain of the correctness of the internal logic. I don't have time to investigate further in the immediate future, so left it unchanged out of caution. ~Andrew
diff --git a/xen/common/bitmap.c b/xen/common/bitmap.c index 7d4551f78283..c57b35f0042c 100644 --- a/xen/common/bitmap.c +++ b/xen/common/bitmap.c @@ -55,7 +55,7 @@ static void clamp_last_byte(uint8_t *bp, unsigned int nbits) bp[nbits/8] &= (1U << remainder) - 1; } -int __bitmap_empty(const unsigned long *bitmap, int bits) +int __bitmap_empty(const unsigned long *bitmap, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -70,7 +70,7 @@ int __bitmap_empty(const unsigned long *bitmap, int bits) } EXPORT_SYMBOL(__bitmap_empty); -int __bitmap_full(const unsigned long *bitmap, int bits) +int __bitmap_full(const unsigned long *bitmap, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -86,7 +86,7 @@ int __bitmap_full(const unsigned long *bitmap, int bits) EXPORT_SYMBOL(__bitmap_full); int __bitmap_equal(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -101,7 +101,7 @@ int __bitmap_equal(const unsigned long *bitmap1, } EXPORT_SYMBOL(__bitmap_equal); -void __bitmap_complement(unsigned long *dst, const unsigned long *src, int bits) +void __bitmap_complement(unsigned long *dst, const unsigned long *src, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -113,7 +113,7 @@ void __bitmap_complement(unsigned long *dst, const unsigned long *src, int bits) EXPORT_SYMBOL(__bitmap_complement); void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k; int nr = BITS_TO_LONGS(bits); @@ -124,7 +124,7 @@ void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_and); void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k; int nr = BITS_TO_LONGS(bits); @@ -135,7 +135,7 @@ void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_or); void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k; int nr = BITS_TO_LONGS(bits); @@ -146,7 +146,7 @@ void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_xor); void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k; int nr = BITS_TO_LONGS(bits); @@ -157,7 +157,7 @@ void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_andnot); int __bitmap_intersects(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -172,7 +172,7 @@ int __bitmap_intersects(const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_intersects); int __bitmap_subset(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits) + const unsigned long *bitmap2, unsigned int bits) { int k, lim = bits/BITS_PER_LONG; for (k = 0; k < lim; ++k) @@ -187,7 +187,7 @@ int __bitmap_subset(const unsigned long *bitmap1, EXPORT_SYMBOL(__bitmap_subset); #if BITS_PER_LONG == 32 -int __bitmap_weight(const unsigned long *bitmap, int bits) +unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int bits) { int k, w = 0, lim = bits/BITS_PER_LONG; @@ -200,7 +200,7 @@ int __bitmap_weight(const unsigned long *bitmap, int bits) return w; } #else -int __bitmap_weight(const unsigned long *bitmap, int bits) +unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int bits) { int k, w = 0, lim = bits/BITS_PER_LONG; diff --git a/xen/include/xen/bitmap.h b/xen/include/xen/bitmap.h index 657390e32ebc..b9f980e91930 100644 --- a/xen/include/xen/bitmap.h +++ b/xen/include/xen/bitmap.h @@ -66,25 +66,25 @@ * lib/bitmap.c provides these functions: */ -extern int __bitmap_empty(const unsigned long *bitmap, int bits); -extern int __bitmap_full(const unsigned long *bitmap, int bits); -extern int __bitmap_equal(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern void __bitmap_complement(unsigned long *dst, const unsigned long *src, - int bits); -extern void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern int __bitmap_intersects(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern int __bitmap_subset(const unsigned long *bitmap1, - const unsigned long *bitmap2, int bits); -extern int __bitmap_weight(const unsigned long *bitmap, int bits); +int __bitmap_empty(const unsigned long *bitmap, unsigned int bits); +int __bitmap_full(const unsigned long *bitmap, unsigned int bits); +int __bitmap_equal(const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +void __bitmap_complement(unsigned long *dst, const unsigned long *src, + unsigned int bits); +void __bitmap_and(unsigned long *dst, const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +void __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +int __bitmap_intersects(const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +int __bitmap_subset(const unsigned long *bitmap1, + const unsigned long *bitmap2, unsigned int bits); +unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int bits); extern void __bitmap_set(unsigned long *map, unsigned int start, int len); extern void __bitmap_clear(unsigned long *map, unsigned int start, int len); @@ -117,7 +117,7 @@ static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) memset(dst, 0, bitmap_bytes(nbits))); } -static inline void bitmap_fill(unsigned long *dst, int nbits) +static inline void bitmap_fill(unsigned long *dst, unsigned int nbits) { size_t nlongs = BITS_TO_LONGS(nbits); @@ -224,7 +224,8 @@ static inline int bitmap_full(const unsigned long *src, unsigned int nbits) return __bitmap_full(src, nbits)); } -static inline int bitmap_weight(const unsigned long *src, int nbits) +static inline unsigned int bitmap_weight(const unsigned long *src, + unsigned int nbits) { return __bitmap_weight(src, nbits); }
Right now, most of the static inline helpers take an unsigned nbits quantity, and most of the library functions take a signed quanity. Because BITMAP_LAST_WORD_MASK() is expressed as a divide, the compiler is forced to emit two different paths to get the correct semantics for signed division. Swap all signed bit-counts to being unsigned bit-counts for the simple cases. This includes the return value of bitmap_weight(). Bloat-o-meter for a random x86 build reports: add/remove: 0/0 grow/shrink: 8/19 up/down: 167/-413 (-246) which all comes from compiler not emitting "dead" logic paths for negative bit counts. No functional change. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: George Dunlap <George.Dunlap@citrix.com> CC: Jan Beulich <JBeulich@suse.com> CC: Stefano Stabellini <sstabellini@kernel.org> CC: Wei Liu <wl@xen.org> CC: Julien Grall <julien@xen.org> Found when investigating negative-shift UBSAN, because each of the library functions ended up being instrumented. There is much more wanting cleaning up here, but we have to start somewhere. Some observations: * Various of the boolean-like return values have -1 for zero-length bitmaps. I can't spot any callers which care, so this seems like a waste. * bitmap_zero() and similar clear predate us switching to use __builtin_memset(), because there's no need for bitmap_switch(). * Should we consolidate 'bits' vs 'nbits'? * The internals of these helpers want converting too. Other helpers need more than just a parameter conversion. --- xen/common/bitmap.c | 24 +++++++++++----------- xen/include/xen/bitmap.h | 43 ++++++++++++++++++++-------------------- 2 files changed, 34 insertions(+), 33 deletions(-)