[PATCH 1/3] btf: add 'extern' linkage for variables [PR106773]

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

Add support for the 'extern' linkage value for BTF_KIND_VAR records,
which is used for variables declared as extern in the source file.

	PR target/106773

gcc/

	* btfout.cc (BTF_LINKAGE_STATIC): New define.
	(BTF_LINKAGE_GLOBAL): Likewise.
	(BTF_LINKAGE_EXTERN): Likewise.
	(btf_collect_datasec): Mark extern variables as such.
	(btf_asm_varent): Accomodate 'extern' linkage.

gcc/testsuite/

	* gcc.dg/debug/btf/btf-variables-4.c: New test.

include/

	* btf.h (struct btf_var): Update comment to note 'extern' linkage.
---
 gcc/btfout.cc                                 |  9 ++++++-
 .../gcc.dg/debug/btf/btf-variables-4.c        | 24 +++++++++++++++++++
 include/btf.h                                 |  2 +-
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index aef9fd70a28..a1c6266a7db 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -66,6 +66,10 @@ static char btf_info_section_label[MAX_BTF_LABEL_BYTES];
 
 #define BTF_INVALID_TYPEID 0xFFFFFFFF
 
+#define BTF_LINKAGE_STATIC 0
+#define BTF_LINKAGE_GLOBAL 1
+#define BTF_LINKAGE_EXTERN 2
+
 /* Mapping of CTF variables to the IDs they will be assigned when they are
    converted to BTF_KIND_VAR type records. Strictly accounts for the index
    from the start of the variable type entries, does not include the number
@@ -314,6 +318,9 @@ btf_collect_datasec (ctf_container_ref ctfc)
 	continue;
 
       const char *section_name = node->get_section ();
+      /* Mark extern variables.  */
+      if (DECL_EXTERNAL (node->decl))
+	dvd->dvd_visibility = BTF_LINKAGE_EXTERN;
 
       if (section_name == NULL)
 	{
@@ -676,7 +683,7 @@ btf_asm_varent (ctf_dvdef_ref var)
   dw2_asm_output_data (4, var->dvd_name_offset, "btv_name");
   dw2_asm_output_data (4, BTF_TYPE_INFO (BTF_KIND_VAR, 0, 0), "btv_info");
   dw2_asm_output_data (4, get_btf_id (var->dvd_type), "btv_type");
-  dw2_asm_output_data (4, (var->dvd_visibility ? 1 : 0), "btv_linkage");
+  dw2_asm_output_data (4, var->dvd_visibility, "btv_linkage");
 }
 
 /* Asm'out a member description following a BTF_KIND_STRUCT or
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c
new file mode 100644
index 00000000000..d77600bae1c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c
@@ -0,0 +1,24 @@
+/* Test BTF generation for extern variables.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* Expect 4 variables.  */
+/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t \]+\[^\n\]*btv_info" 4 } } */
+
+/* 2 extern, 1 global, 1 static.  */
+/* { dg-final { scan-assembler-times "\[\t \]0\[\t \]+\[^\n\]*btv_linkage" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x1\[\t \]+\[^\n\]*btv_linkage" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x2\[\t \]+\[^\n\]*btv_linkage" 2 } } */
+
+extern int a;
+extern const int b;
+int c;
+static const int d = 5;
+
+int foo (int x)
+{
+  c = a + b + x;
+
+  return c + d;
+}
diff --git a/include/btf.h b/include/btf.h
index eba67f9d599..9a757ce5bc9 100644
--- a/include/btf.h
+++ b/include/btf.h
@@ -182,7 +182,7 @@ struct btf_param
    information about the variable.  */
 struct btf_var
 {
-  uint32_t linkage;	/* Currently only 0=static or 1=global.  */
+  uint32_t linkage;	/* 0=static, 1=global, 2=extern.  */
 };
 
 /* BTF_KIND_DATASEC is followed by VLEN struct btf_var_secinfo entries,
-- 
2.38.1