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Various fixes for floating point on RISC-V.

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- Explicitly load an empty initial state into FP registers when taking
  the fault on the first FP instruction in a thread.  Setting
  SSTATE.FS to INITIAL is just a marker to let context switch restore
  code know that it can load FP registers with zeroes instead of
  memory loads.  It does not imply that the hardware will reset all
  registers to zero on first access.  In addition, set the state to
  CLEAN instead of INITIAL after the first FP instruction.
  cpu_switch() doesn't do anything for INITIAL and only restores from
  the pcb if the state is CLEAN.  We could perhaps change cpu_switch
  to call fpe_state_clear if the state was INITIAL and leave SSTATE.FS
  set to INITIAL instead of CLEAN after the first FP instruction.
  However, adding this complexity to cpu_switch() doesn't seem worth
  the supposed gain.
- Only save the current FPU registers in fill_fpregs() if the request
  is made to save the current thread's registers.  Previously if a
  debugger requested FP registers via ptrace() it was getting a copy
  of the debugger's FP registers rather than the debugee's.
- Zero the entire FP register set structure returned for ptrace() if a
  thread hasn't used FP registers rather than leaking garbage in the
  fp_fcsr field.
- If a debugger writes FP registers via ptrace(), always mark the pcb
  as having valid FP registers and set SSTATUS.FS_MASK to CLEAN so
  that the registers will be restored when the debugged thread
  resumes.
- Be more explicit about clearing the SSTATUS.FS field before setting
  it to CLEAN on the first FP instruction trap.

Submitted by:	br, markj
Approved by:	re (rgrimes)
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D17141
This commit is contained in:
John Baldwin 2018-09-19 23:45:18 +00:00
parent 31ce875385
commit 232d0b87e0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=338814
4 changed files with 68 additions and 3 deletions
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1
sys/riscv/include/fpe.h
View File

@ -34,5 +34,6 @@
#define _MACHINE_FPE_H_
void fpe_state_save(struct thread *td);
void fpe_state_clear(void);
#endif /* !_MACHINE_FPE_H_ */

10
sys/riscv/riscv/machdep.c
View File

@ -204,13 +204,14 @@ fill_fpregs(struct thread *td, struct fpreg *regs)
* If we have just been running FPE instructions we will
* need to save the state to memcpy it below.
*/
fpe_state_save(td);
if (td == curthread)
fpe_state_save(td);
memcpy(regs->fp_x, pcb->pcb_x, sizeof(regs->fp_x));
regs->fp_fcsr = pcb->pcb_fcsr;
} else
#endif
memset(regs->fp_x, 0, sizeof(regs->fp_x));
memset(regs, 0, sizeof(*regs));
return (0);
}
@ -219,12 +220,17 @@ int
set_fpregs(struct thread *td, struct fpreg *regs)
{
#ifdef FPE
struct trapframe *frame;
struct pcb *pcb;
frame = td->td_frame;
pcb = td->td_pcb;
memcpy(pcb->pcb_x, regs->fp_x, sizeof(regs->fp_x));
pcb->pcb_fcsr = regs->fp_fcsr;
pcb->pcb_fpflags |= PCB_FP_STARTED;
frame->tf_sstatus &= ~SSTATUS_FS_MASK;
frame->tf_sstatus |= SSTATUS_FS_CLEAN;
#endif
return (0);

53
sys/riscv/riscv/swtch.S
View File

@ -153,6 +153,59 @@ ENTRY(fpe_state_save)
END(fpe_state_save)
#endif /* FPE */
/*
* void
* fpe_state_clear(void)
*/
ENTRY(fpe_state_clear)
/*
* Enable FPE usage in supervisor mode,
* so we can access registers.
*/
li t0, SSTATUS_FS_INITIAL
csrs sstatus, t0
fscsr zero
fcvt.d.l f0, zero
fcvt.d.l f1, zero
fcvt.d.l f2, zero
fcvt.d.l f3, zero
fcvt.d.l f4, zero
fcvt.d.l f5, zero
fcvt.d.l f6, zero
fcvt.d.l f7, zero
fcvt.d.l f8, zero
fcvt.d.l f9, zero
fcvt.d.l f10, zero
fcvt.d.l f11, zero
fcvt.d.l f12, zero
fcvt.d.l f13, zero
fcvt.d.l f14, zero
fcvt.d.l f15, zero
fcvt.d.l f16, zero
fcvt.d.l f17, zero
fcvt.d.l f18, zero
fcvt.d.l f19, zero
fcvt.d.l f20, zero
fcvt.d.l f21, zero
fcvt.d.l f22, zero
fcvt.d.l f23, zero
fcvt.d.l f24, zero
fcvt.d.l f25, zero
fcvt.d.l f26, zero
fcvt.d.l f27, zero
fcvt.d.l f28, zero
fcvt.d.l f29, zero
fcvt.d.l f30, zero
fcvt.d.l f31, zero
/* Disable FPE usage in supervisor mode. */
li t0, SSTATUS_FS_MASK
csrc sstatus, t0
ret
END(fpe_state_clear)
/*
* void cpu_throw(struct thread *old, struct thread *new)
*/

7
sys/riscv/riscv/trap.c
View File

@ -57,6 +57,9 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_param.h>
#include <vm/vm_extern.h>
#ifdef FPE
#include <machine/fpe.h>
#endif
#include <machine/frame.h>
#include <machine/pcb.h>
#include <machine/pcpu.h>
@ -363,7 +366,9 @@ do_trap_user(struct trapframe *frame)
* May be a FPE trap. Enable FPE usage
* for this thread and try again.
*/
frame->tf_sstatus |= SSTATUS_FS_INITIAL;
fpe_state_clear();
frame->tf_sstatus &= ~SSTATUS_FS_MASK;
frame->tf_sstatus |= SSTATUS_FS_CLEAN;
pcb->pcb_fpflags |= PCB_FP_STARTED;
break;
}