pussuw commented on code in PR #8227:
URL: https://github.com/apache/nuttx/pull/8227#discussion_r1085666671
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arch/risc-v/src/common/riscv_swint.c:
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@@ -497,8 +515,16 @@ int riscv_swint(int irq, void *context, void *arg)
if (index == 0 && rtcb->xcp.kstack != NULL)
{
rtcb->xcp.ustkptr = (uintptr_t *)regs[REG_SP];
- regs[REG_SP] = (uintptr_t)rtcb->xcp.kstack +
+ if (rtcb->xcp.kstkptr == NULL)
Review Comment:
The original check (== NULL) is actually correct. However, the original
implementation is very difficult to follow and understand. I can't know how it
was supposed to work, only that it was broken.
Without this check, i.e. unconditionally setting
`regs[REG_SP] = (uintptr_t)rtcb->xcp.kstack + ARCH_KERNEL_STACKSIZE;`
Destroys the entire kernel stack frame, because it resets the stack pointer
to stack top. If rtcb->xcp.kstkptr == NULL we know that no one is using the
kernel stack atm and we can set the stack to stack top. Otherwise we should not
touch regs[REG_SP].
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