[PATCH] btf: do not skip emitting void variables [PR106773]

[David Faust via Gcc-patches]

The eBPF loader expects to find BTF_KIND_VAR records for references to
extern const void symbols. We were mistakenly identifing these as
unsupported types, and as a result skipping emitting VAR records for
them.

Tested on bpf-unknown-none and x86_64, no known regressions.
OK?

Thanks.

gcc/ChangeLog:

        PR target/106773
        * btfout.cc (btf_dvd_emit_preprocess_cb): Do not skip emitting
        variables which refer to void types.

gcc/testsuite/ChangeLog:

        PR target/106773
        * gcc.dg/debug/btf/btf-pr106773.c: New test.
---
 gcc/btfout.cc                                 |  2 +-
 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c | 21 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 997a33fa089..37ec662c190 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -430,7 +430,7 @@ btf_dvd_emit_preprocess_cb (ctf_dvdef_ref *slot, 
ctf_container_ref arg_ctfc)
   ctf_dvdef_ref var = (ctf_dvdef_ref) * slot;
 
   /* Do not add variables which refer to unsupported types.  */
-  if (btf_removed_type_p (var->dvd_type))
+  if (!voids.contains (var->dvd_type) && btf_removed_type_p (var->dvd_type))
     return 1;
 
   arg_ctfc->ctfc_vars_list[num_vars_added] = var;
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c 
b/gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c
new file mode 100644
index 00000000000..4de15f76546
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c
@@ -0,0 +1,21 @@
+/* Test BTF generation for extern const void symbols.
+   BTF_KIND_VAR records should be emitted for such symbols if they are used.  
*/
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* Expect 1 variable record only for foo.  */
+/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t 
\]+\[^\n\]*btv_info" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x1\[\t \]+\[^\n\]*btv_linkage" 1 
} } */
+
+/* { dg-final { scan-assembler-times "ascii \"foo.0\"\[\t 
\]+\[^\n\]*btf_string" 1 } } */
+
+extern const void foo;
+extern const void bar;
+
+unsigned long func () {
+  unsigned long x = (unsigned long) &foo;
+
+  return x;
+}
+
-- 
2.36.1