On 10/10/26 9:27 PM, Karl Mehltretter wrote:
stack_trace_save() uses skipnr + 1 because arch_stack_walk() is expected
to first report the return into stack_trace_save(). With FRAME_POINTER,
the RISC-V arch_stack_walk() calls walk_stackframe(), which starts from
its own frame and first reports the return into arch_stack_walk().
stack_trace_save() therefore starts one frame too early. For example,
page_owner records begin at __set_page_owner() instead of the allocation
site.
Move the walker into an always-inlined helper and call it directly from
arch_stack_walk(). Keep walk_stackframe() as a wrapper for its existing
callers.
return_address() skips level + 3 entries, while the arm64 implementation
skips level + 2. After removing the extra frame, use level + 2 so
ftrace_return_address() and CALLER_ADDR results do not shift by one caller.
Fixes: 6a00ef449370 ("riscv: eliminate unreliable __builtin_frame_address(1)")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <[email protected]>
---
Tested with the KUnit suite from patch 2 on QEMU's virt machine, clang 22
(LLVM=1), on af32da41b032:
mainline stack_trace_save 0/3, return_address 2/2
stacktrace.c change alone stack_trace_save 3/3, return_address 0/2
this patch stack_trace_save 3/3, return_address 2/2
A BeagleV Ahead (TH1520) booted with this patch passes all five cases.
The stack_trace_save() result on mainline (0/3) was also reproduced with
GCC 15.2 and QEMU 10.2.1.
Without CONFIG_FRAME_POINTER the walker scans the stack for anything that
looks like a text address and its start frame is not exact before or
after this patch. What return_address() returns there is unchanged: the
walk loses one leading entry and the skip count goes down by one.
The reliable unwinder series [1] rewrites this walker and has the correct
start frame for stack_trace_save() as a side effect, but leaves
return_address() at level + 3. This patch conflicts with 5/7 of that
series; if that goes in first, only the return_address.c hunk is needed.
[1] https://lore.kernel.org/r/[email protected]
Hi Karl,
Now that 7.4-rc1 is out and neither your two patches nor the reliable
unwinder series made this merge window, I'm preparing v7 of the series
for the next one.
Are you OK with folding your patches into the livepatch series rather
than keeping two conflicting walkers in flight?
Thanks.
Shuai
