Unverified Commit 51356ce6 authored by Clément Léger's avatar Clément Léger Committed by Palmer Dabbelt
Browse files

riscv: stacktrace: fix backtracing through exceptions 



Prior to commit 5d5fc33c ("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: 5d5fc33c ("riscv: Improve exception and system call latency")
Signed-off-by: default avatarClément Léger <cleger@rivosinc.com>
Tested-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20241209155714.1239665-1-cleger@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent f754f27e

arch/riscv/kernel/entry.S

+1 −0
Original line number Diff line number Diff line
@@ -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)

arch/riscv/kernel/stacktrace.c

+3 −1
Original line number Diff line number Diff line
@@ -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;