[gcc r13-2255] bpf: handle anonymous members in CO-RE reloc [PR106745]

[David Faust <dfaust@gcc.gnu.org>]

https://gcc.gnu.org/g:b504149d2c92ddfcfab62ea6d1ed49ae72493e38

commit r13-2255-gb504149d2c92ddfcfab62ea6d1ed49ae72493e38
Author: David Faust <david.faust@oracle.com>
Date:   Mon Aug 29 11:21:52 2022 -0700

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

Diff:
---
 gcc/config/bpf/coreout.cc                    | 16 +++++++++------
 gcc/testsuite/gcc.target/bpf/core-pr106745.c | 30 ++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/gcc/config/bpf/coreout.cc b/gcc/config/bpf/coreout.cc
index cceaaa969cc..8897a045ea1 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 +221,21 @@ 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++;
+	  bool field_has_btf = get_btf_id (dmd->dmd_type) <= BTF_MAX_TYPE;
+
+	  if (field == node)
+	    return field_has_btf ? i : -1;
+
+	  if (field_has_btf)
+	    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 } } */