Re: [PATCH v4 4/6] powerpc64/bpf: Add arch_bpf_stack_walk() for BPF JIT

From: Abhishek Dubey <redacted>

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 <redacted>
---
  arch/powerpc/net/bpf_jit_comp64.c | 28 ++++++++++++++++++++++++++++
  1 file changed, 28 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 18da5a866447..c25ba1ad587a 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c

@@ -247,6 +247,34 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
  	bpf_jit_build_fentry_stubs(image, ctx);
  }
  
+void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64), void *cookie)
+{
+	// callback processing always in current context
+	unsigned long fp = current_stack_frame();
+
+	for (;;) {
+		unsigned long *frame = (unsigned long *) fp;
+		unsigned long ip;
+
+		if (!validate_sp(fp, current))
+			return;
+
+		ip = frame[STACK_FRAME_LR_SAVE];
+		if (!ip)
+			break;
+
+		/*
+		 * consume_fn common code expects stack pointer(sp) in third
+		 * argument. There is no sp in ppc64, rather pass frame
+		 * pointer.
+		 */
+		if (ip && !consume_fn(cookie, ip, fp, fp))
+			break;
+
+		fp = frame[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;