On Thu, Mar 06, 2025 at 08:29:51PM +0900, Vincent Mailhol via B4 Relay wrote: > Introduce some fixed width variant of the GENMASK() and the BIT() > macros in bits.h. Note that the main goal is not to get the correct > type, but rather to enforce more checks at compile time. For example: > > GENMASK_U16(16, 0) > > will raise a build bug. > > This series is a continuation of: > > https://lore.kernel.org/intel-xe/20240208074521.577076-1-lucas.demarchi@xxxxxxxxx > > from Lucas De Marchi. Above series is one year old. I really think > that this was a good idea and I do not want this series to die. So I > am volunteering to revive it. > > Meanwhile, many changes occurred in bits.h. The most significant > change is that __GENMASK() was moved to the uapi headers. > > In v4 an onward, I introduce one big change: split the definition of > the asm and non-asm GENMASK(). I think this is controversial. > Especially, Yury commented that he did not want such split. So I > initially implemented a first draft in which both the asm and non-asm > version would rely on the same helper macro, i.e. adding this: > > #define __GENMASK_t(t, w, h, l) \ I thought we agreed on renaming... > (((t)~_ULL(0) - ((t)1 << (l)) + 1) & \ > ((t)~_ULL(0) >> (w - 1 - (h)))) > > to uapi/bits.h. And then, the different GENMASK()s would look like > this: > > #define __GENMASK(h, l) __GENMASK_t(unsigned long, __BITS_PER_LONG, h, l) Ditto. > and so on. > > I implemented it, and the final result looks quite ugly. Not only do > we need to manually provide the width each time, the biggest concern > is that adding this to the uapi is asking for trouble. Who knows how > people are going to use this? And once it is in the uapi, there is > virtually no way back. > > Finally, I do not think it makes sense to expose the fixed width > variants to the asm. The fixed width integers type are a C > concept. For asm, the long and long long variants seems sufficient. > > And so, after implementing both, the asm and non-asm split seems way > more clean and I think this is the best compromise. Let me know what > you think :) > > As requested, here are the bloat-o-meter stats: > > $ ./scripts/bloat-o-meter vmlinux_before.o vmlinux_after.o > add/remove: 0/0 grow/shrink: 4/2 up/down: 5/-4 (1) > Function old new delta > intel_psr_invalidate 666 668 +2 > mst_stream_compute_config 1652 1653 +1 > intel_psr_flush 977 978 +1 > intel_dp_compute_link_config 1327 1328 +1 > cfg80211_inform_bss_data 5109 5108 -1 > intel_drrs_activate 379 376 -3 > Total: Before=22723481, After=22723482, chg +0.00% > > (done with GCC 12.4.1 on a defconfig) What defconfig? x86_64_defconfig? -- With Best Regards, Andy Shevchenko
