Re: [Qemu-devel] [PATCH-4.2 v1 4/6] target/riscv: Create function to test if FP is enabled

[Alistair Francis <alistair23@gmail.com>]

On Tue, Jul 30, 2019 at 1:49 AM Christophe de Dinechin
<dinechin@redhat.com> wrote:
>
>
> Alistair Francis writes:
>
> > Let's creaate a function that tests if floating point support is
>
> Typo: create

Fixed

>
> > enabled. We can then protect all floating point operations based on if
> > they are enabled.
> >
> > This patch so far doesn't change anything, it's just preparing for the
> > Hypervisor support for floating point operations.
> >
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  target/riscv/cpu.h        |  6 +++++-
> >  target/riscv/cpu_helper.c | 10 ++++++++++
> >  target/riscv/csr.c        | 19 ++++++++++---------
> >  3 files changed, 25 insertions(+), 10 deletions(-)
> >
> > diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> > index 0adb307f32..2dc9b17678 100644
> > --- a/target/riscv/cpu.h
> > +++ b/target/riscv/cpu.h
> > @@ -255,6 +255,7 @@ void riscv_cpu_do_interrupt(CPUState *cpu);
> >  int riscv_cpu_gdb_read_register(CPUState *cpu, uint8_t *buf, int reg);
> >  int riscv_cpu_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg);
> >  bool riscv_cpu_exec_interrupt(CPUState *cs, int interrupt_request);
> > +bool riscv_cpu_fp_enabled(CPURISCVState *env);
> >  int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch);
> >  hwaddr riscv_cpu_get_phys_page_debug(CPUState *cpu, vaddr addr);
> >  void  riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
> > @@ -298,7 +299,10 @@ static inline void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong *pc,
> >  #ifdef CONFIG_USER_ONLY
> >      *flags = TB_FLAGS_MSTATUS_FS;
> >  #else
> > -    *flags = cpu_mmu_index(env, 0) | (env->mstatus & MSTATUS_FS);
> > +    *flags = cpu_mmu_index(env, 0);
> > +    if (riscv_cpu_fp_enabled(env)) {
> > +        *flags |= env->mstatus & MSTATUS_FS;
> > +    }
> >  #endif
> >  }
> >
> > diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> > index f027be7f16..225e407cff 100644
> > --- a/target/riscv/cpu_helper.c
> > +++ b/target/riscv/cpu_helper.c
> > @@ -71,6 +71,16 @@ bool riscv_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
> >
> >  #if !defined(CONFIG_USER_ONLY)
> >
> > +/* Return true is floating point support is currently enabled */
> > +bool riscv_cpu_fp_enabled(CPURISCVState *env)
> > +{
> > +    if (env->mstatus & MSTATUS_FS) {
> > +        return true;
> > +    }
> > +
> > +    return false;
>
> Will there be more conditions that lead to the "true" case?
> If not, please consider making it a one-liner for readability, e.g.
>
>    return env->mstatus & MSTATUS_FS;
>
> (just a personal preference, feel free to ignore)

There are going to be more conditionals when adding the Hypervisor extension.

>
> > +}
> > +
> >  int riscv_cpu_claim_interrupts(RISCVCPU *cpu, uint32_t interrupts)
> >  {
> >      CPURISCVState *env = &cpu->env;
> > diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> > index af3b762c8b..7b73b73cf7 100644
> > --- a/target/riscv/csr.c
> > +++ b/target/riscv/csr.c
> > @@ -46,7 +46,7 @@ void riscv_set_csr_ops(int csrno, riscv_csr_operations *ops)
> >  static int fs(CPURISCVState *env, int csrno)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
>
> This was existing behavior, but I'm curious why all these
> tests are disabled when env->debugger is set. This was introduced
> in 753e3fe20, but I see no rationale in the commit message.
> I find it odd, maybe even suspicious, that activating the debugger
> would change the behavior :-)

This is to allow GDB to access the registers.

>
> >          return -1;
> >      }
> >  #endif
> > @@ -108,7 +108,7 @@ static int pmp(CPURISCVState *env, int csrno)
> >  static int read_fflags(CPURISCVState *env, int csrno, target_ulong *val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >  #endif
> > @@ -119,7 +119,7 @@ static int read_fflags(CPURISCVState *env, int csrno, target_ulong *val)
> >  static int write_fflags(CPURISCVState *env, int csrno, target_ulong val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >      env->mstatus |= MSTATUS_FS;
> > @@ -131,7 +131,7 @@ static int write_fflags(CPURISCVState *env, int csrno, target_ulong val)
> >  static int read_frm(CPURISCVState *env, int csrno, target_ulong *val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >  #endif
> > @@ -142,7 +142,7 @@ static int read_frm(CPURISCVState *env, int csrno, target_ulong *val)
> >  static int write_frm(CPURISCVState *env, int csrno, target_ulong val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >      env->mstatus |= MSTATUS_FS;
> > @@ -154,7 +154,7 @@ static int write_frm(CPURISCVState *env, int csrno, target_ulong val)
> >  static int read_fcsr(CPURISCVState *env, int csrno, target_ulong *val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >  #endif
> > @@ -166,7 +166,7 @@ static int read_fcsr(CPURISCVState *env, int csrno, target_ulong *val)
> >  static int write_fcsr(CPURISCVState *env, int csrno, target_ulong val)
> >  {
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
> > +    if (!env->debugger && !riscv_cpu_fp_enabled(env)) {
> >          return -1;
> >      }
> >      env->mstatus |= MSTATUS_FS;
> > @@ -307,6 +307,7 @@ static int write_mstatus(CPURISCVState *env, int csrno, target_ulong val)
> >  {
> >      target_ulong mstatus = env->mstatus;
> >      target_ulong mask = 0;
> > +    int dirty;
> >
> >      /* flush tlb on mstatus fields that affect VM */
> >      if (env->priv_ver <= PRIV_VERSION_1_09_1) {
> > @@ -340,8 +341,8 @@ static int write_mstatus(CPURISCVState *env, int csrno, target_ulong val)
> >
> >      mstatus = (mstatus & ~mask) | (val & mask);
> >
> > -    int dirty = ((mstatus & MSTATUS_FS) == MSTATUS_FS) |
> > -                ((mstatus & MSTATUS_XS) == MSTATUS_XS);
> > +    dirty = riscv_cpu_fp_enabled(env) |
> > +            ((mstatus & MSTATUS_XS) == MSTATUS_XS);
> >      mstatus = set_field(mstatus, MSTATUS_SD, dirty);
> >      env->mstatus = mstatus;
>
> Reviewed-by: Christophe de Dinechin <dinechin@redhat.com>

Thanks!

Alistair

>
> --
> Cheers,
> Christophe de Dinechin (IRC c3d)