Hi Linus,
On Sun, Jan 5, 2025 at 10:51 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, 3 Jan 2025 at 01:22, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
Perhaps this is an issue with sparse?
No, this is just m68k doing disgusting things that happen to work with
gcc, because gcc considers casts to be lvalues (which in turn is comes
from some horrid C++ thing, since in C++ casting is a whole magical
extra complexity).
IOW, this m68k pattern is horrendous, and sparse quite reasonably
complains about it:
#define umul_ppmm(w1, w0, u, v) \
__asm__ ("mulu%.l %3,%1:%0" \
: "=d" ((USItype)(w0)), \
"=d" ((USItype)(w1)) \
: "%0" ((USItype)(u)), \
"dmi" ((USItype)(v)))
notice how it has two register outputs (the "=d"), and the destination
of said output is not a proper lvalue, but a cast expression.
I think you could just remove the cast. Afaik the w0/w1 arguments come from
#define __umulsidi3(u, v) \
({DIunion __w; \
umul_ppmm (__w.s.high, __w.s.low, u, v); \
__w.ll; })
and __w.s.high and __w.s.low are from struct DIstruct, which uses
"SItype". So all the cast does is to change the signedness of the
variable, but that has no *meaning* when you assign to it and the
sizes match.
Alternatively, you could just use the right types explicitly and write
the umul_ppmm() macro something like
#define umul_ppmm(w1, w0, u, v) do { \
USItype __w0, __w1; \
__asm__ ("mulu%.l %3,%1:%0" \
: "=d" (__w0) \
"=d" (__w1) \
: "%0" ((USItype)(u)), \
"dmi" ((USItype)(v))); \
w0 = __w0; w1 = __w1; } while (0)
NOTE! UNTESTED! Treat the above as a "something like this, perhaps".
Thank you, using intermediate variables instead of casts for the output
operands gets rid of the lvalue-related sparse warnings.
That leaves us with the "not addressable" sparse error. Apparently
that goes away by dropping the cast on the last input operand,
so I will introduce intermediate variables for all input operands, too.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
