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arch/risc-v: fix stale ustkptr used for backtrace in kernel stack mode

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xcp.ustkptr is only assigned once in up_initial_state() when a task is
created and, since the syscall fast path was optimized in
e6973c764c, is never updated afterwards. up_backtrace() used
"ustkptr != NULL" to decide whether a task is currently blocked
inside a syscall, and *(ustkptr + 1) as the frame pointer to resume
tracing from. Since ustkptr is now a dead value fixed at task
creation time, the check is always true and the "frame pointer" it
derives points at stale data near the initial stack top, unrelated
to where the task is actually blocked.

Use rtcb->flags & TCB_FLAG_SYSCALL together with xcp.sregs, which
dispatch_syscall() maintains precisely across the entire syscall
execution window (including any nested context switches caused by
blocking), to locate the frame pointer/return address saved at
syscall entry instead.

Signed-off-by: liang.huang <liang.huang@houmo.ai>
This commit is contained in:
liang.huang 2026-07-15 12:12:57 +08:00 • committed by Xiang Xiao
parent 335aacbf1a
commit bdfa666f3e
1 changed files with 6 additions and 4 deletions
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10
arch/risc-v/src/common/riscv_backtrace.c
View file

@ -180,12 +180,13 @@ int up_backtrace(struct tcb_s *tcb, void **buffer, int size, int skip)
else
{
#ifdef CONFIG_ARCH_KERNEL_STACK
if (rtcb->xcp.ustkptr != NULL)
if ((rtcb->flags & TCB_FLAG_SYSCALL) != 0)
{
ret = backtrace(rtcb->stack_base_ptr, (uintptr_t *)
((uintptr_t)rtcb->stack_base_ptr +
rtcb->adj_stack_size),
(void *)*(rtcb->xcp.ustkptr + 1), NULL,
(void *)rtcb->xcp.sregs[REG_FP],
(void *)rtcb->xcp.sregs[REG_EPC],
buffer, size, &skip);
}
else
@ -201,12 +202,13 @@ int up_backtrace(struct tcb_s *tcb, void **buffer, int size, int skip)
else
{
#ifdef CONFIG_ARCH_KERNEL_STACK
if (tcb->xcp.ustkptr != NULL)
if ((tcb->flags & TCB_FLAG_SYSCALL) != 0)
{
ret = backtrace(tcb->stack_base_ptr,
(uintptr_t *)((uintptr_t)tcb->stack_base_ptr +
tcb->adj_stack_size),
(void *)*(tcb->xcp.ustkptr + 1), NULL,
(void *)tcb->xcp.sregs[REG_FP],
(void *)tcb->xcp.sregs[REG_EPC],
buffer, size, &skip);
}
else