On Thu, 14 Sep 2023 15:54:54 +0300 Michael Tokarev <[email protected]> wrote:
> 13.09.2023 18:05, Jonathan Cameron via wrote: > > Indexing has to be done into an array with the right size elements. > > As such, the size parameter always matches the array element size > > and can be used in place of the longer sizeof(*array) > > > > Signed-off-by: Jonathan Cameron <[email protected]> > > --- > > hw/cxl/cxl-component-utils.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/hw/cxl/cxl-component-utils.c b/hw/cxl/cxl-component-utils.c > > index f3bbf0fd13..089e10b232 100644 > > --- a/hw/cxl/cxl-component-utils.c > > +++ b/hw/cxl/cxl-component-utils.c > > @@ -76,7 +76,7 @@ static uint64_t cxl_cache_mem_read_reg(void *opaque, > > hwaddr offset, > > if (cregs->special_ops && cregs->special_ops->read) { > > return cregs->special_ops->read(cxl_cstate, offset, size); > > } else { > > - return cregs->cache_mem_registers[offset / > > sizeof(*cregs->cache_mem_registers)]; > > + return cregs->cache_mem_registers[offset / size]; > > This is a though one, and smells wrong. > > Though because it is not at all obvious where this "size" value comes from, > have to find usage(s) of this function (cache_mem_ops) and think twice about > the other parameters in there. Also having in mind the previous comparison > with 8. In this part of the code, size should always be =4, but it takes > hard time to figure this out. > > Wrong - no, because of the above - the only 2 possible values are 4 and 8, > but it's difficult to see what's going on, and you're making it worse. > > Original code was at least clear you're getting a single register from > an array of registers, with new code it is not clear at all. Fair point. > > What I'd probably use here is to add comment that size can be either 4 or 8, > and use a switch similar to what you've used in first patch in this series. > And have a static_assert(sizeof(register) == 4) or something like that > here in this second branch. Good idea. > > So it is something like: > > static uint64_t cxl_cache_mem_read_reg(void *opaque, hwaddr offset, > unsigned size) > { > CXLComponentState *cxl_cstate = opaque; > ComponentRegisters *cregs = &cxl_cstate->crb; > > switch (size) { > case 8: > qemu_log_mask(LOG_UNIMP, > "CXL 8 byte cache mem registers not implemented\n"); > return 0; > > case 4: > if (cregs->special_ops && cregs->special_ops->read) { > return cregs->special_ops->read(cxl_cstate, offset, 4); > } else { > return cregs->cache_mem_registers[offset / > > sizeof(*cregs->cache_mem_registers)]; > } > > default: > /* this routine is called with size being either 4 or 8 only */ > g_assert_not_reached(); > } > } > > Note: I especially left the sizeof() here, instead of using a previously > suggested static_assert() - because a register can be implemented using > larger integers on the host, it does not need to be 4 bytes, - but only > low 4 bytes can actually be used. I don't follow. Here cache_mem_registers is an array of uint32_t so it is going to be 4 bytes on any host! Obviously that's not true for registers in general. So I've added the assert as it is always valid and made it a / 4 Note I ended up with just using size in the first place because I was planning to add a local variable that was always the same size and that was silly. > > This does not shorten the line (it does by wrapping it up), but it keep > code correct and more understandable. Adding size parameter there makes > it much more cryptic. > > Here and in other places. > > This is just an example, not a suggestion. It makes sense. Sorry - thought I'd sent this last week! Jonathan > > /mjt >
