[PATCH] bpf: handle anonymous members in CO-RE reloc [PR106745]

[David Faust <david.faust@oracle.com>]

The old method for computing a member index for a CO-RE relocation
relied on a name comparison, which could SEGV if the member in question
is itself part of an anonymous inner struct or union.

This patch changes the index computation to not rely on a name, while
maintaining the ability to account for other sibling fields which may
not have a representation in BTF.

Tested in bpf-unknown-none, no known regressions.
OK?

Thanks.

gcc/ChangeLog:

	PR target/106745
	* config/bpf/coreout.cc (bpf_core_get_sou_member_index): Fix
	computation of index for anonymous members.

gcc/testsuite/ChangeLog:

	PR target/106745
	* gcc.target/bpf/core-pr106745.c: New test.
---
 gcc/config/bpf/coreout.cc                    | 19 +++++++++----
 gcc/testsuite/gcc.target/bpf/core-pr106745.c | 30 ++++++++++++++++++++
 2 files changed, 44 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/bpf/core-pr106745.c

diff --git a/gcc/config/bpf/coreout.cc b/gcc/config/bpf/coreout.cc
index cceaaa969cc..caad4380fa1 100644
--- a/gcc/config/bpf/coreout.cc
+++ b/gcc/config/bpf/coreout.cc
@@ -207,7 +207,6 @@ bpf_core_get_sou_member_index (ctf_container_ref ctfc, const tree node)
   if (TREE_CODE (node) == FIELD_DECL)
     {
       const tree container = DECL_CONTEXT (node);
-      const char * name = IDENTIFIER_POINTER (DECL_NAME (node));
 
       /* Lookup the CTF type info for the containing type.  */
       dw_die_ref die = lookup_type_die (container);
@@ -222,16 +221,26 @@ bpf_core_get_sou_member_index (ctf_container_ref ctfc, const tree node)
       if (kind != CTF_K_STRUCT && kind != CTF_K_UNION)
         return -1;
 
+      tree field = TYPE_FIELDS (container);
       int i = 0;
       ctf_dmdef_t * dmd;
       for (dmd = dtd->dtd_u.dtu_members;
            dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd))
         {
           if (get_btf_id (dmd->dmd_type) > BTF_MAX_TYPE)
-            continue;
-          if (strcmp (dmd->dmd_name, name) == 0)
-            return i;
-          i++;
+	    {
+	      /* This field does not have a BTF representation.  */
+	      if (field == node)
+		return -1;
+	    }
+	  else
+	    {
+	      if (field == node)
+		return i;
+	      i++;
+	    }
+
+	  field = DECL_CHAIN (field);
         }
     }
   return -1;
diff --git a/gcc/testsuite/gcc.target/bpf/core-pr106745.c b/gcc/testsuite/gcc.target/bpf/core-pr106745.c
new file mode 100644
index 00000000000..9d347006a69
--- /dev/null
+++ b/gcc/testsuite/gcc.target/bpf/core-pr106745.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA -mco-re" } */
+
+struct weird
+{
+  struct
+  {
+    int b;
+  };
+
+  char x;
+
+  union
+  {
+    int a;
+    int c;
+  };
+};
+
+
+int test (struct weird *arg) {
+  int *x = __builtin_preserve_access_index (&arg->b);
+  int *y = __builtin_preserve_access_index (&arg->c);
+
+  return *x + *y;
+}
+
+
+/* { dg-final { scan-assembler-times "ascii \"0:0:0.0\"\[\t \]+\[^\n\]*btf_aux_string" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"0:2:1.0\"\[\t \]+\[^\n\]*btf_aux_string" 1 } } */
-- 
2.36.1