powerpc64/bpf: Add arch_bpf_stack_walk() for BPF JIT

This function is used by bpf_throw() to unwind the stack
until frame of exception-boundary during BPF exception
handling.

This function is necessary to support BPF exceptions on
PowerPC.

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260124075223.6033-5-adubey@linux.ibm.com

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index e3f677eaa41ce4537a358e331c4b9cb77dbad9dd..f97907cc5ed4ca8f16d44f86fe5e82a131d08182 100644 (file)
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -247,6 +247,47 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
        bpf_jit_build_fentry_stubs(image, ctx);
 }
 
+/*
+ * arch_bpf_stack_walk() - BPF stack walker for PowerPC
+ *
+ * Based on arch_stack_walk() from stacktrace.c.
+ * PowerPC uses stack frames rather than stack pointers. See [1] for
+ * the equivalence between frame pointers and stack pointers.
+ * Additional reference at [2].
+ * TODO: refactor with arch_stack_walk()
+ *
+ * [1]: https://lore.kernel.org/all/20200220115141.2707-1-mpe@ellerman.id.au/
+ * [2]: https://lore.kernel.org/bpf/20260122211854.5508-5-adubey@linux.ibm.com/
+ */
+
+void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64), void *cookie)
+{
+       // callback processing always in current context
+       unsigned long sp = current_stack_frame();
+
+       for (;;) {
+               unsigned long *stack = (unsigned long *) sp;
+               unsigned long ip;
+
+               if (!validate_sp(sp, current))
+                       return;
+
+               ip = stack[STACK_FRAME_LR_SAVE];
+               if (!ip)
+                       break;
+
+               /*
+                * consume_fn common code expects stack pointer in third
+                * argument. There is no sp in ppc64, rather pass frame
+                * pointer(named sp here).
+                */
+               if (ip && !consume_fn(cookie, ip, sp, sp))
+                       break;
+
+               sp = stack[0];
+       }
+}
+
 int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
 {
        unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0;