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8ac71d7e46
The following two reasons cause FP registers are sometimes not
initialized before starting the user program.
1. Currently, the FP context is initialized in flush_thread() function
and we expect these initial values to be restored to FP register when
doing FP context switch. However, the FP context switch only occurs in
switch_to function. Hence, if this process does not be scheduled out
and scheduled in before entering the user space, the FP registers
have no chance to initialize.
2. In flush_thread(), the state of reg->sstatus.FS inherits from the
parent. Hence, the state of reg->sstatus.FS may be dirty. If this
process is scheduled out during flush_thread() and initializing the
FP register, the fstate_save() in switch_to will corrupt the FP context
which has been initialized until flush_thread().
To solve the 1st case, the initialization of the FP register will be
completed in start_thread(). It makes sure all FP registers are initialized
before starting the user program. For the 2nd case, the state of
reg->sstatus.FS in start_thread will be set to SR_FS_OFF to prevent this
process from corrupting FP context in doing context save. The FP state is
set to SR_FS_INITIAL in start_trhead().
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Fixes:
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|---|---|---|
| .. | ||
| vdso | ||
| .gitignore | ||
| asm-offsets.c | ||
| cacheinfo.c | ||
| cpu.c | ||
| cpufeature.c | ||
| entry.S | ||
| fpu.S | ||
| ftrace.c | ||
| head.S | ||
| irq.c | ||
| Makefile | ||
| mcount-dyn.S | ||
| mcount.S | ||
| module-sections.c | ||
| module.c | ||
| module.lds | ||
| perf_event.c | ||
| process.c | ||
| ptrace.c | ||
| reset.c | ||
| riscv_ksyms.c | ||
| setup.c | ||
| signal.c | ||
| smp.c | ||
| smpboot.c | ||
| stacktrace.c | ||
| sys_riscv.c | ||
| syscall_table.c | ||
| time.c | ||
| traps.c | ||
| vdso.c | ||
| vmlinux.lds.S | ||