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fixed bug for syscall example

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The original logic of setting mstatus has problem.
The or directive cannot set .MPP to 0.

Optimize the original code and use csrs and csrc instead.

Note we cannot assume the default value of mstatus is zero.
rvos may not be the first one to run on the system/virt.
It just so lucky that the initial value of mstatus is zero
on QEMU/virt.

Signed-off-by: Wang Chen <wangchen20@iscas.ac.cn>
This commit is contained in:
Wang Chen
2024-03-25 21:06:11 +08:00
committed by Chen Wang
parent 4698c95063
commit 992b0ba91c
4 changed files with 14 additions and 18 deletions
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7
code/os/08-preemptive/start.S
View File

@@ -32,13 +32,12 @@ _start:
# At the end of start_kernel, schedule() will call MRET to switch
# to the first task, so we parepare the mstatus here.
# Notice: default mstatus is 0
# Notice: It is best not to assume that the initial value of mstatus is
# zero.
# Set mstatus.MPP to 3, so we still run in Machine mode after MRET.
# Set mstatus.MPIE to 1, so MRET will enable the interrupt.
li t0, 3 << 11 | 1 << 7
csrr a1, mstatus
or t0, t0, a1
csrw mstatus, t0
csrs mstatus, t0
j start_kernel # hart 0 jump to c

7
code/os/09-lock/start.S
View File

@@ -32,13 +32,12 @@ _start:
# At the end of start_kernel, schedule() will call MRET to switch
# to the first task, so we parepare the mstatus here.
# Notice: default mstatus is 0
# Notice: It is best not to assume that the initial value of mstatus is
# zero.
# Set mstatus.MPP to 3, so we still run in Machine mode after MRET.
# Set mstatus.MPIE to 1, so MRET will enable the interrupt.
li t0, 3 << 11 | 1 << 7
csrr a1, mstatus
or t0, t0, a1
csrw mstatus, t0
csrs mstatus, t0
j start_kernel # hart 0 jump to c

7
code/os/10-swtimer/start.S
View File

@@ -32,13 +32,12 @@ _start:
# At the end of start_kernel, schedule() will call MRET to switch
# to the first task, so we parepare the mstatus here.
# Notice: default mstatus is 0
# Notice: It is best not to assume that the initial value of mstatus is
# zero.
# Set mstatus.MPP to 3, so we still run in Machine mode after MRET.
# Set mstatus.MPIE to 1, so MRET will enable the interrupt.
li t0, 3 << 11 | 1 << 7
csrr a1, mstatus
or t0, t0, a1
csrw mstatus, t0
csrs mstatus, t0
j start_kernel # hart 0 jump to c

11
code/os/11-syscall/start.S
View File

@@ -50,22 +50,21 @@ _start:
# At the end of start_kernel, schedule() will call MRET to switch
# to the first task, so we parepare the mstatus here.
# Notice: default mstatus is 0
# Notice: It is best not to assume that the initial value of mstatus is
# zero.
#ifdef CONFIG_SYSCALL
# Set mstatus.MPP as 0, so we will run in User mode after MRET.
# No need to set mstatus.MPIE to 1 explicitly, because according to ISA
# specification: interrupts for M-mode, which is higher than U-mode, are
# always globally enabled regardless of the setting of the global MIE bit.
# So finally we simply reset t0 to zero.
li t0, 0
li t0, 3 << 11
csrc mstatus, t0
#else
# Set mstatus.MPP to 3, so we still run in Machine mode after MRET.
# Set mstatus.MPIE to 1, so MRET will enable the interrupt.
li t0, 3 << 11 | 1 << 7
csrs mstatus, t0
#endif
csrr a1, mstatus
or t0, t0, a1
csrw mstatus, t0
j start_kernel # hart 0 jump to c