Re: [musl] [PATCH] riscv: Fix setjmp assembly when compiling for ilp32f/lp64f.

["Alex Rønne Petersen" <alex@alexrp.com>]

On Tue, Jul 23, 2024 at 11:22 PM Szabolcs Nagy <nsz@port70.net> wrote:
>
> * Alex Rønne Petersen <alex@alexrp.com> [2024-06-29 04:04:34 +0200]:
> > To keep things simple, I just changed the instruction mnemonics appropriately,
> > rather than adding complexity by changing the buffer size/offsets based on ABI.
> >
> > Signed-off-by: Alex Rønne Petersen <alex@alexrp.com>
>
> fwiw this looks good to me.
>
> the only weirdness is that the math code uses __riscv_flen
> and this code __riscv_float_abi*. i don't know if there
> is semantic difference.

`__riscv_flen` tells you the width of the FP registers on the target
CPU. This is semantically distinct from `__riscv_float_abi`. For
example, while it would probably be a bit silly, there's no particular
reason why I couldn't target the LP64F ABI on an RV64IMAFDC machine.
In that case, no code needs to concern itself with the upper bits of
the FP registers.

I took a quick peek at some of the `__riscv_flen` checks in musl. They
look ok. They're checking the capabilities of the machine for the
purposes of performing a computation; they're not making ABI
decisions. In my silly example above, if I tell the compiler to do so
with `-march=rv64...d`, it would theoretically be fine for the
compiler to generate double-precision float instructions for
computations as long as values are passed/returned according to LP64F
rules.

>
> > ---
> >  src/setjmp/riscv32/longjmp.S | 30 ++++++++++++++++++------------
> >  src/setjmp/riscv32/setjmp.S  | 30 ++++++++++++++++++------------
> >  src/setjmp/riscv64/longjmp.S | 30 ++++++++++++++++++------------
> >  src/setjmp/riscv64/setjmp.S  | 30 ++++++++++++++++++------------
> >  4 files changed, 72 insertions(+), 48 deletions(-)
> >
> > diff --git a/src/setjmp/riscv32/longjmp.S b/src/setjmp/riscv32/longjmp.S
> > index f9cb3318..b4e5458d 100644
> > --- a/src/setjmp/riscv32/longjmp.S
> > +++ b/src/setjmp/riscv32/longjmp.S
> > @@ -23,18 +23,24 @@ longjmp:
> >       lw ra,    52(a0)
> >
> >  #ifndef __riscv_float_abi_soft
> > -     fld fs0,  56(a0)
> > -     fld fs1,  64(a0)
> > -     fld fs2,  72(a0)
> > -     fld fs3,  80(a0)
> > -     fld fs4,  88(a0)
> > -     fld fs5,  96(a0)
> > -     fld fs6,  104(a0)
> > -     fld fs7,  112(a0)
> > -     fld fs8,  120(a0)
> > -     fld fs9,  128(a0)
> > -     fld fs10, 136(a0)
> > -     fld fs11, 144(a0)
> > +#ifdef __riscv_float_abi_double
> > +#define FLX fld
> > +#else
> > +#define FLX flw
> > +#endif
> > +
> > +     FLX fs0,  56(a0)
> > +     FLX fs1,  64(a0)
> > +     FLX fs2,  72(a0)
> > +     FLX fs3,  80(a0)
> > +     FLX fs4,  88(a0)
> > +     FLX fs5,  96(a0)
> > +     FLX fs6,  104(a0)
> > +     FLX fs7,  112(a0)
> > +     FLX fs8,  120(a0)
> > +     FLX fs9,  128(a0)
> > +     FLX fs10, 136(a0)
> > +     FLX fs11, 144(a0)
> >  #endif
> >
> >       seqz a0, a1
> > diff --git a/src/setjmp/riscv32/setjmp.S b/src/setjmp/riscv32/setjmp.S
> > index 8a75cf55..5a1a41ef 100644
> > --- a/src/setjmp/riscv32/setjmp.S
> > +++ b/src/setjmp/riscv32/setjmp.S
> > @@ -23,18 +23,24 @@ setjmp:
> >       sw ra,    52(a0)
> >
> >  #ifndef __riscv_float_abi_soft
> > -     fsd fs0,  56(a0)
> > -     fsd fs1,  64(a0)
> > -     fsd fs2,  72(a0)
> > -     fsd fs3,  80(a0)
> > -     fsd fs4,  88(a0)
> > -     fsd fs5,  96(a0)
> > -     fsd fs6,  104(a0)
> > -     fsd fs7,  112(a0)
> > -     fsd fs8,  120(a0)
> > -     fsd fs9,  128(a0)
> > -     fsd fs10, 136(a0)
> > -     fsd fs11, 144(a0)
> > +#ifdef __riscv_float_abi_double
> > +#define FSX fsd
> > +#else
> > +#define FSX fsw
> > +#endif
> > +
> > +     FSX fs0,  56(a0)
> > +     FSX fs1,  64(a0)
> > +     FSX fs2,  72(a0)
> > +     FSX fs3,  80(a0)
> > +     FSX fs4,  88(a0)
> > +     FSX fs5,  96(a0)
> > +     FSX fs6,  104(a0)
> > +     FSX fs7,  112(a0)
> > +     FSX fs8,  120(a0)
> > +     FSX fs9,  128(a0)
> > +     FSX fs10, 136(a0)
> > +     FSX fs11, 144(a0)
> >  #endif
> >
> >       li a0, 0
> > diff --git a/src/setjmp/riscv64/longjmp.S b/src/setjmp/riscv64/longjmp.S
> > index 41e2d210..982475c7 100644
> > --- a/src/setjmp/riscv64/longjmp.S
> > +++ b/src/setjmp/riscv64/longjmp.S
> > @@ -23,18 +23,24 @@ longjmp:
> >       ld ra,    104(a0)
> >
> >  #ifndef __riscv_float_abi_soft
> > -     fld fs0,  112(a0)
> > -     fld fs1,  120(a0)
> > -     fld fs2,  128(a0)
> > -     fld fs3,  136(a0)
> > -     fld fs4,  144(a0)
> > -     fld fs5,  152(a0)
> > -     fld fs6,  160(a0)
> > -     fld fs7,  168(a0)
> > -     fld fs8,  176(a0)
> > -     fld fs9,  184(a0)
> > -     fld fs10, 192(a0)
> > -     fld fs11, 200(a0)
> > +#ifdef __riscv_float_abi_double
> > +#define FLX fld
> > +#else
> > +#define FLX flw
> > +#endif
> > +
> > +     FLX fs0,  112(a0)
> > +     FLX fs1,  120(a0)
> > +     FLX fs2,  128(a0)
> > +     FLX fs3,  136(a0)
> > +     FLX fs4,  144(a0)
> > +     FLX fs5,  152(a0)
> > +     FLX fs6,  160(a0)
> > +     FLX fs7,  168(a0)
> > +     FLX fs8,  176(a0)
> > +     FLX fs9,  184(a0)
> > +     FLX fs10, 192(a0)
> > +     FLX fs11, 200(a0)
> >  #endif
> >
> >       seqz a0, a1
> > diff --git a/src/setjmp/riscv64/setjmp.S b/src/setjmp/riscv64/setjmp.S
> > index 51249672..0795bf7d 100644
> > --- a/src/setjmp/riscv64/setjmp.S
> > +++ b/src/setjmp/riscv64/setjmp.S
> > @@ -23,18 +23,24 @@ setjmp:
> >       sd ra,    104(a0)
> >
> >  #ifndef __riscv_float_abi_soft
> > -     fsd fs0,  112(a0)
> > -     fsd fs1,  120(a0)
> > -     fsd fs2,  128(a0)
> > -     fsd fs3,  136(a0)
> > -     fsd fs4,  144(a0)
> > -     fsd fs5,  152(a0)
> > -     fsd fs6,  160(a0)
> > -     fsd fs7,  168(a0)
> > -     fsd fs8,  176(a0)
> > -     fsd fs9,  184(a0)
> > -     fsd fs10, 192(a0)
> > -     fsd fs11, 200(a0)
> > +#ifdef __riscv_float_abi_double
> > +#define FSX fsd
> > +#else
> > +#define FSX fsw
> > +#endif
> > +
> > +     FSX fs0,  112(a0)
> > +     FSX fs1,  120(a0)
> > +     FSX fs2,  128(a0)
> > +     FSX fs3,  136(a0)
> > +     FSX fs4,  144(a0)
> > +     FSX fs5,  152(a0)
> > +     FSX fs6,  160(a0)
> > +     FSX fs7,  168(a0)
> > +     FSX fs8,  176(a0)
> > +     FSX fs9,  184(a0)
> > +     FSX fs10, 192(a0)
> > +     FSX fs11, 200(a0)
> >  #endif
> >
> >       li a0, 0
> > --
> > 2.40.1