WIP: selftests/bpf: Fix test task_pt_regs on arm 32-bit

Have error:

  test_task_pt_regs:PASS:uprobe_offset 0 nsec
  test_task_pt_regs:PASS:skel_open 0 nsec
  test_task_pt_regs:PASS:check_bss 0 nsec
  test_task_pt_regs:PASS:attach_uprobe 0 nsec
  test_task_pt_regs:FAIL:check_uprobe_res unexpected check_uprobe_res: actual 0 != expected 1
  torvalds#424     task_pt_regs:FAIL

due to progs/test_task_pt_regs.c using:

  #define PT_REGS_SIZE sizeof(struct pt_regs)

which is non-CORE and evaluates to wrong size in 64-bit BPF VM.

Workaround is using bpf_core_type_size() to limit the actual read but
leave the potentially larger PT_REGS_SIZE for the allocation.

Signed-off-by: Tony Ambardar <[email protected]>

Author: guidosarducci

tools/testing/selftests/bpf/progs/test_task_pt_regs.c

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "vmlinux.h"
-#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
 #include <bpf/bpf_tracing.h>
 
 #define PT_REGS_SIZE sizeof(struct pt_regs)
@@ -19,12 +19,14 @@ int handle_uprobe(struct pt_regs *ctx)
 {
 	struct task_struct *current;
 	struct pt_regs *regs;
+	int regs_size;
 
 	current = bpf_get_current_task_btf();
 	regs = (struct pt_regs *) bpf_task_pt_regs(current);
-	if (bpf_probe_read_kernel(current_regs, PT_REGS_SIZE, regs))
+	regs_size = bpf_core_type_size(struct pt_regs);
+	if (bpf_probe_read_kernel(current_regs, regs_size, regs))
 		return 0;
-	if (bpf_probe_read_kernel(ctx_regs, PT_REGS_SIZE, ctx))
+	if (bpf_probe_read_kernel(ctx_regs, regs_size, ctx))
 		return 0;
 
 	/* Prove that uprobe was run */