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riscv: stacktrace: fix backtracing through exceptions

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Prior to commit 5d5fc33ce5 ("riscv: Improve exception and system call
latency"), backtrace through exception worked since ra was filled with
ret_from_exception symbol address and the stacktrace code checked 'pc' to
be equal to that symbol. Now that handle_exception uses regular 'call'
instructions, this isn't working anymore and backtrace stops at
handle_exception(). Since there are multiple call site to C code in the
exception handling path, rather than checking multiple potential return
addresses, add a new symbol at the end of exception handling and check pc
to be in that range.

Fixes: 5d5fc33ce5 ("riscv: Improve exception and system call latency")
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20241209155714.1239665-1-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Clément Léger 2024-12-09 16:57:12 +01:00 • committed by Palmer Dabbelt
parent f754f27e98
commit 51356ce60e
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GPG key ID: 2E1319F35FBB1889
2 changed files with 4 additions and 1 deletions
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1
arch/riscv/kernel/entry.S
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@ -278,6 +278,7 @@ SYM_CODE_START_NOALIGN(ret_from_exception)
#else
sret
#endif
SYM_INNER_LABEL(ret_from_exception_end, SYM_L_GLOBAL)
SYM_CODE_END(ret_from_exception)
ASM_NOKPROBE(ret_from_exception)

4
arch/riscv/kernel/stacktrace.c
View file

@ -17,6 +17,7 @@
#ifdef CONFIG_FRAME_POINTER
extern asmlinkage void handle_exception(void);
extern unsigned long ret_from_exception_end;
static inline int fp_is_valid(unsigned long fp, unsigned long sp)
{
@ -71,7 +72,8 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
fp = frame->fp;
pc = ftrace_graph_ret_addr(current, &graph_idx, frame->ra,
&frame->ra);
if (pc == (unsigned long)handle_exception) {
if (pc >= (unsigned long)handle_exception &&
pc < (unsigned long)&ret_from_exception_end) {
if (unlikely(!__kernel_text_address(pc) || !fn(arg, pc)))
break;