[PATCH v2] Fixed problem with BTF defining smaller enums.

[Cupertino Miranda]

Hi everyone,

David: Thanks for the v1 review.

This version adds the following;
 - test case,
 - improves condition logic,
 - fixes mask typo.

Looking forward to your review.

v1 at: https://gcc.gnu.org/pipermail/gcc-patches/2023-November/636391.html

Cheers,
Cupertino


commit 3f89d352a4ee90882089142d743f8a748013b5fe
Author: Cupertino Miranda <cupertino.mira...@oracle.com>
Date:   Fri Nov 10 14:02:30 2023 +0000

    Fixed problem with BTF defining smaller enums.
    
    This patch fixes a BTF, which would become invalid when having
    smaller then 4 byte definitions of enums.
    For example, when using the __attribute__((mode(byte))) in the enum
    definition.
    
    Two problems were identified:
     - it would incorrectly create an entry for enum64 when the size of the
       enum was different then 4.
     - it would allocate less then 4 bytes for the value entry in BTF, in
       case the type was smaller.
    
    BTF generated was validated against clang.
    
    gcc/ChangeLog:
            * bpfout.cc (btf_calc_num_vbytes): Fixed logic for enum64.
            (btf_asm_enum_const): Corrected logic for enum64 and smaller
            than 4 bytes values.
    
    gcc/testsuite/ChangeLog:
            gcc.dg/debug/btf/btf-enum-small.c: Added test.

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index e07fed302c24..5f2e99ce4725 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -299,7 +299,7 @@ btf_calc_num_vbytes (ctf_dtdef_ref dtd)
       break;
 
     case BTF_KIND_ENUM:
-      vlen_bytes += (dtd->dtd_data.ctti_size == 0x8)
+      vlen_bytes += (dtd->dtd_data.ctti_size > 4)
 			? vlen * sizeof (struct btf_enum64)
 			: vlen * sizeof (struct btf_enum);
       break;
@@ -914,8 +914,8 @@ btf_asm_enum_const (unsigned int size, ctf_dmdef_t * dmd, unsigned int idx)
 {
   dw2_asm_output_data (4, dmd->dmd_name_offset, "ENUM_CONST '%s' idx=%u",
 		       dmd->dmd_name, idx);
-  if (size == 4)
-    dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
+  if (size <= 4)
+    dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
   else
     {
       dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
new file mode 100644
index 000000000000..eb8a1bd2c438
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
@@ -0,0 +1,28 @@
+/* Test BTF generation for small enums.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -gbtf -dA" } */
+
+/* { dg-final { scan-assembler-not "bte_value_lo32" } } */
+/* { dg-final { scan-assembler-not "bte_value_hi32" } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x6000002\[\t \]+\[^\n\]*btt_info" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALL' idx=0" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALLY' idx=1" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALL.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALLY.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "bte_value" 2 } } */
+
+enum smalled_enum
+{
+  eSMALL,
+  eSMALLY,
+} __attribute__((mode(byte)));
+
+struct root_struct {
+  enum smalled_enum esmall;
+};
+
+enum smalled_enum
+foo(struct root_struct *root) {
+  return root->esmall;
+}