[PATCH v2 0/3] btf: fix BTF for extern items [PR106773]

[PATCH v2 0/3] btf: fix BTF for extern items [PR106773]

[David Faust]

[Changes from v1:
 - Remove #defines for LINKAGE_* values, instead mirror enums from
   linux/btf.h to include/btf.h and use those.
 - Fix BTF generation for extern variable with both non-defining and
   defining decls in the same CU. Add a test for this.
 - Update several comments per review feedback. ]

Hi,

This series fixes the issues reported in target/PR106773. I decided to
split it into three commits, as there are ultimately three distinct
issues and fixes. See each patch for details.

Tested on bpf-unknown-none and x86_64-linux-gnu, no known regressions.

OK to push?
Thanks.

David Faust (3):
  btf: add 'extern' linkage for variables [PR106773]
  btf: fix 'extern const void' variables [PR106773]
  btf: correct generation for extern funcs [PR106773]

 gcc/btfout.cc                                 | 184 +++++++++++++-----
 .../gcc.dg/debug/btf/btf-datasec-2.c          |  28 +++
 .../gcc.dg/debug/btf/btf-function-6.c         |  19 ++
 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c |  25 +++
 .../gcc.dg/debug/btf/btf-variables-4.c        |  24 +++
 .../gcc.dg/debug/btf/btf-variables-5.c        |  19 ++
 include/btf.h                                 |  29 ++-
 7 files changed, 276 insertions(+), 52 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c

-- 
2.38.1

[PATCH v2 1/3] btf: add 'extern' linkage for variables [PR106773]

[David Faust]

[Changes from v1:
 - Add enum btf_var_linkage in include/btf.h and use that instead of
   local #defines.
 - Fix BTF generation for extern variable with both non-defining and
   defining decls in the same CU. Add a test for this. ]

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

This also fixes a bug with BTF generation for extern variables which
have both a non-defining declaration and a defining declaration in the
same CU.

	PR target/106773

gcc/

	* btfout.cc (btf_collect_datasec): Mark extern variables as such.
	(btf_dvd_emit_preprocess_cb): Skip non-defining extern variable decl
	if there is a defining decl for the same variable.
	(btf_asm_varent): Accomodate 'extern' linkage.

gcc/testsuite/

	* gcc.dg/debug/btf/btf-variables-4.c: New test.
	* gcc.dg/debug/btf/btf-variables-5.c: New test.

include/

	* btf.h (enum btf_var_linkage): New.
	(struct btf_var): Update comment to note 'extern' linkage.
---
 gcc/btfout.cc                                 | 11 ++++++++-
 .../gcc.dg/debug/btf/btf-variables-4.c        | 24 +++++++++++++++++++
 .../gcc.dg/debug/btf/btf-variables-5.c        | 19 +++++++++++++++
 include/btf.h                                 | 11 ++++++++-
 4 files changed, 63 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index aef9fd70a28..677e8324424 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -314,6 +314,9 @@ 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_VAR_GLOBAL_EXTERN;
 
       if (section_name == NULL)
 	{
@@ -431,6 +434,12 @@ btf_dvd_emit_preprocess_cb (ctf_dvdef_ref *slot, ctf_container_ref arg_ctfc)
 {
   ctf_dvdef_ref var = (ctf_dvdef_ref) * slot;
 
+  /* If this is an extern variable declaration with a defining declaration
+     later, skip it so that only the defining declaration is emitted.
+     This is the same case, fix and reasoning as in CTF; see PR105089.  */
+  if (ctf_dvd_ignore_lookup (arg_ctfc, var->dvd_key))
+    return 1;
+
   /* Do not add variables which refer to unsupported types.  */
   if (btf_removed_type_p (var->dvd_type))
     return 1;
@@ -676,7 +685,7 @@ 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/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c
new file mode 100644
index 00000000000..8aae76cacab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c
@@ -0,0 +1,19 @@
+/* Test BTF generation for extern variable with both non-defining and
+   defining declarations.
+
+   In this case, only a single variable record should be emitted,
+   with 'global' linkage. However two array types will be generated.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* Expect 1 variable with global (1) linkage.  */
+/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t \]+\[^\n\]*btv_info" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x1\[\t \]+\[^\n\]*btv_linkage" 1 } } */
+
+/* Expect 2 array types, one of which is unsized.  */
+/* { dg-final { scan-assembler-times "\[\t \]0x4\[\t \]+\[^\n\]*bta_nelems" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0\[\t \]+\[^\n\]*bta_nelems" 1 } } */
+
+extern const char FOO[];
+const char FOO[] = "foo";
diff --git a/include/btf.h b/include/btf.h
index eba67f9d599..da621353aa1 100644
--- a/include/btf.h
+++ b/include/btf.h
@@ -178,11 +178,20 @@ struct btf_param
   uint32_t type;	/* Type of parameter.  */
 };
 
+/* BTF_KIND_VAR records encode linkage information in a single
+   trailing struct btf_var.  These are the supported values.  */
+enum btf_var_linkage
+{
+  BTF_VAR_STATIC = 0,
+  BTF_VAR_GLOBAL_ALLOCATED = 1,
+  BTF_VAR_GLOBAL_EXTERN = 2,
+};
+
 /* BTF_KIND_VAR is followed by a single struct btf_var, which describes
    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

[PATCH v2 2/3] btf: fix 'extern const void' variables [PR106773]

[David Faust]

[Changes from v1: Minor updates to comments per review. ]

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.

In addition, the internal DWARF representation from which BTF is
produced does not generate 'const' modifier DIEs for the void type,
which meant in BTF the 'const' qualifier was dropped for 'extern const
void' variables. This patch also adds support for generating a const
void type in BTF to correct emission for these variables.

	PR target/106773

gcc/

	* btfout.cc (btf_collect_datasec): Correct size of void entries.
	(btf_dvd_emit_preprocess_cb): Do not skip emitting variables which
	refer to void types.
	(btf_init_postprocess): Create 'const void' type record if needed and
	adjust variables to refer to it as appropriate.

gcc/testsuite/

	* gcc.dg/debug/btf/btf-pr106773.c: New test.
---
 gcc/btfout.cc                                 | 44 +++++++++++++++++--
 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c | 25 +++++++++++
 2 files changed, 65 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 677e8324424..204b11d4e9f 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -350,6 +350,8 @@ btf_collect_datasec (ctf_container_ref ctfc)
       tree size = DECL_SIZE_UNIT (node->decl);
       if (tree_fits_uhwi_p (size))
 	info.size = tree_to_uhwi (size);
+      else if (VOID_TYPE_P (TREE_TYPE (node->decl)))
+	info.size = 1;
 
       /* Offset is left as 0 at compile time, to be filled in by loaders such
 	 as libbpf.  */
@@ -441,7 +443,7 @@ btf_dvd_emit_preprocess_cb (ctf_dvdef_ref *slot, ctf_container_ref arg_ctfc)
     return 1;
 
   /* 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;
@@ -1075,15 +1077,49 @@ btf_init_postprocess (void)
 {
   ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
 
-  size_t i;
-  size_t num_ctf_types = tu_ctfc->ctfc_types->elements ();
-
   holes.create (0);
   voids.create (0);
 
   num_types_added = 0;
   num_types_created = 0;
 
+  /* Workaround for 'const void' variables.  These variables are sometimes used
+     in eBPF programs to address kernel symbols.  DWARF does not generate const
+     qualifier on void type, so we would incorrectly emit these variables
+     without the const qualifier.
+     Unfortunately we need the TREE node to know it was const, and we need
+     to create the const modifier type (if needed) now, before making the types
+     list.  So we can't avoid iterating with FOR_EACH_VARIABLE here, and then
+     again when creating the DATASEC entries.  */
+  ctf_id_t constvoid_id = CTF_NULL_TYPEID;
+  varpool_node *var;
+  FOR_EACH_VARIABLE (var)
+    {
+      if (!var->decl)
+	continue;
+
+      tree type = TREE_TYPE (var->decl);
+      if (type && VOID_TYPE_P (type) && TYPE_READONLY (type))
+	{
+	  dw_die_ref die = lookup_decl_die (var->decl);
+	  if (die == NULL)
+	    continue;
+
+	  ctf_dvdef_ref dvd = ctf_dvd_lookup (tu_ctfc, die);
+	  if (dvd == NULL)
+	    continue;
+
+	  /* Create the 'const' modifier type for void.  */
+	  if (constvoid_id == CTF_NULL_TYPEID)
+	    constvoid_id = ctf_add_reftype (tu_ctfc, CTF_ADD_ROOT,
+					    dvd->dvd_type, CTF_K_CONST, NULL);
+	  dvd->dvd_type = constvoid_id;
+	}
+    }
+
+  size_t i;
+  size_t num_ctf_types = tu_ctfc->ctfc_types->elements ();
+
   if (num_ctf_types)
     {
       init_btf_id_map (num_ctf_types + 1);
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..f90fa773a4b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c
@@ -0,0 +1,25 @@
+/* Test BTF generation for extern const void symbols.
+   BTF_KIND_VAR records should be emitted for such symbols if they are used,
+   as well as a corresponding entry in the appropriate DATASEC record.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* Expect 1 variable record only for foo, with 'extern' (2) linkage.  */
+/* { dg-final { scan-assembler-times "\[\t \]0xe000000\[\t \]+\[^\n\]*btv_info" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x2\[\t \]+\[^\n\]*btv_linkage" 1 } } */
+
+/* { dg-final { scan-assembler-times "ascii \"foo.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+
+/* { dg-final { scan-assembler-times "0\[\t \]+\[^\n\]*bts_offset" 1 } } */
+/* { dg-final { scan-assembler-times "1\[\t \]+\[^\n\]*bts_size" 1 } } */
+
+extern const void foo __attribute__((weak)) __attribute__((section (".ksyms")));
+extern const void bar __attribute__((weak)) __attribute__((section (".ksyms")));
+
+unsigned long func () {
+  unsigned long x = (unsigned long) &foo;
+
+  return x;
+}
+
-- 
2.38.1

[PATCH v2 3/3] btf: correct generation for extern funcs [PR106773]

[David Faust]

[Changes from v1:
 - Add enum btf_func_linkage to include/btf.h and use it.
 - Minor updates to comments based on review. ]

The eBPF loader expects to find entries for functions declared as extern
in the corresponding BTF_KIND_DATASEC record, but we were not generating
these entries.

This patch adds support for the 'extern' linkage of function types in
BTF, and creates entries for for them BTF_KIND_DATASEC records as needed.

	PR target/106773

gcc/

	* btfout.cc (get_section_name): New function.
	(btf_collect_datasec): Use it here. Process functions, marking them
	'extern' and generating DATASEC entries for them as appropriate. Move
	creation of BTF_KIND_FUNC records to here...
	(btf_dtd_emit_preprocess_cb): ... from here.

gcc/testsuite/

	* gcc.dg/debug/btf/btf-datasec-2.c: New test.
	* gcc.dg/debug/btf/btf-function-6.c: New test.

include/

	* btf.h (enum btf_func_linkage): New.
	(struct btf_var_secinfo): Update comments with notes about extern
	functions.
---
 gcc/btfout.cc                                 | 129 ++++++++++++------
 .../gcc.dg/debug/btf/btf-datasec-2.c          |  28 ++++
 .../gcc.dg/debug/btf/btf-function-6.c         |  19 +++
 include/btf.h                                 |  18 ++-
 4 files changed, 148 insertions(+), 46 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c
 create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 204b11d4e9f..a423fabc0b5 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -290,7 +290,35 @@ btf_datasec_push_entry (ctf_container_ref ctfc, const char *secname,
   ds.entries.safe_push (info);
 
   datasecs.safe_push (ds);
-  num_types_created++;
+}
+
+
+/* Return the section name, as of interest to btf_collect_datasec, for the
+   given symtab node.  Note that this deliberately returns NULL for objects
+   which do not go in a section btf_collect_datasec cares about.  */
+static const char *
+get_section_name (symtab_node *node)
+{
+  const char *section_name = node->get_section ();
+
+  if (section_name == NULL)
+    {
+      switch (categorize_decl_for_section (node->decl, 0))
+	{
+	case SECCAT_BSS:
+	  section_name = ".bss";
+	  break;
+	case SECCAT_DATA:
+	  section_name = ".data";
+	  break;
+	case SECCAT_RODATA:
+	  section_name = ".rodata";
+	  break;
+	default:;
+	}
+    }
+
+  return section_name;
 }
 
 /* Construct all BTF_KIND_DATASEC records for CTFC. One such record is created
@@ -301,7 +329,60 @@ btf_datasec_push_entry (ctf_container_ref ctfc, const char *secname,
 static void
 btf_collect_datasec (ctf_container_ref ctfc)
 {
-  /* See cgraph.h struct symtab_node, which varpool_node extends.  */
+  cgraph_node *func;
+  FOR_EACH_FUNCTION (func)
+    {
+      dw_die_ref die = lookup_decl_die (func->decl);
+      if (die == NULL)
+	continue;
+
+      ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die);
+      if (dtd == NULL)
+	continue;
+
+      /* Functions actually get two types: a BTF_KIND_FUNC_PROTO, and
+	 also a BTF_KIND_FUNC.  But the CTF container only allocates one
+	 type per function, which matches closely with BTF_KIND_FUNC_PROTO.
+	 For each such function, also allocate a BTF_KIND_FUNC entry.
+	 These will be output later.  */
+      ctf_dtdef_ref func_dtd = ggc_cleared_alloc<ctf_dtdef_t> ();
+      func_dtd->dtd_data = dtd->dtd_data;
+      func_dtd->dtd_data.ctti_type = dtd->dtd_type;
+      func_dtd->linkage = dtd->linkage;
+      func_dtd->dtd_type = num_types_added + num_types_created;
+
+      /* Only the BTF_KIND_FUNC type actually references the name. The
+	 BTF_KIND_FUNC_PROTO is always anonymous.  */
+      dtd->dtd_data.ctti_name = 0;
+
+      vec_safe_push (funcs, func_dtd);
+      num_types_created++;
+
+      /* Mark any 'extern' funcs and add DATASEC entries for them.  */
+      if (DECL_EXTERNAL (func->decl))
+	{
+	  func_dtd->linkage = BTF_FUNC_EXTERN;
+
+	  const char *section_name = get_section_name (func);
+	  /* Note: get_section_name () returns NULL for functions in text
+	     section.  This is intentional, since we do not want to generate
+	     DATASEC entries for them.  */
+	  if (section_name == NULL)
+	    continue;
+
+	  struct btf_var_secinfo info;
+
+	  /* +1 for the sentinel type not in the types map.  */
+	  info.type = func_dtd->dtd_type + 1;
+
+	  /* Both zero at compile time.  */
+	  info.size = 0;
+	  info.offset = 0;
+
+	  btf_datasec_push_entry (ctfc, section_name, info);
+	}
+    }
+
   varpool_node *node;
   FOR_EACH_VARIABLE (node)
     {
@@ -313,28 +394,13 @@ btf_collect_datasec (ctf_container_ref ctfc)
       if (dvd == NULL)
 	continue;
 
-      const char *section_name = node->get_section ();
       /* Mark extern variables.  */
       if (DECL_EXTERNAL (node->decl))
 	dvd->dvd_visibility = BTF_VAR_GLOBAL_EXTERN;
 
+      const char *section_name = get_section_name (node);
       if (section_name == NULL)
-	{
-	  switch (categorize_decl_for_section (node->decl, 0))
-	    {
-	    case SECCAT_BSS:
-	      section_name = ".bss";
-	      break;
-	    case SECCAT_DATA:
-	      section_name = ".data";
-	      break;
-	    case SECCAT_RODATA:
-	      section_name = ".rodata";
-	      break;
-	    default:
-	      continue;
-	    }
-	}
+	continue;
 
       struct btf_var_secinfo info;
 
@@ -359,6 +425,8 @@ btf_collect_datasec (ctf_container_ref ctfc)
 
       btf_datasec_push_entry (ctfc, section_name, info);
     }
+
+  num_types_created += datasecs.length ();
 }
 
 /* Return true if the type ID is that of a type which will not be emitted (for
@@ -463,29 +531,6 @@ btf_dtd_emit_preprocess_cb (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
   if (!btf_emit_id_p (dtd->dtd_type))
     return;
 
-  uint32_t btf_kind
-    = get_btf_kind (CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info));
-
-  if (btf_kind == BTF_KIND_FUNC_PROTO)
-    {
-      /* Functions actually get two types: a BTF_KIND_FUNC_PROTO, and
-	 also a BTF_KIND_FUNC. But the CTF container only allocates one
-	 type per function, which matches closely with BTF_KIND_FUNC_PROTO.
-	 For each such function, also allocate a BTF_KIND_FUNC entry.
-	 These will be output later.  */
-      ctf_dtdef_ref func_dtd = ggc_cleared_alloc<ctf_dtdef_t> ();
-      func_dtd->dtd_data = dtd->dtd_data;
-      func_dtd->dtd_data.ctti_type = dtd->dtd_type;
-      func_dtd->linkage = dtd->linkage;
-
-      vec_safe_push (funcs, func_dtd);
-      num_types_created++;
-
-      /* Only the BTF_KIND_FUNC type actually references the name. The
-	 BTF_KIND_FUNC_PROTO is always anonymous.  */
-      dtd->dtd_data.ctti_name = 0;
-    }
-
   ctfc->ctfc_num_vlen_bytes += btf_calc_num_vbytes (dtd);
 }
 
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c b/gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c
new file mode 100644
index 00000000000..f4b298cf019
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c
@@ -0,0 +1,28 @@
+/* Test BTF generation of DATASEC records for extern functions.
+
+   Only functions declared extern should have entries in DATASEC records.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* Expect one DATASEC with vlen=1 (.foo_sec) and one with vlen=2 (.bar_sec) */
+/* { dg-final { scan-assembler-times "0xf000002\[\t \]+\[^\n\]*btt_info" 1 } } */
+/* { dg-final { scan-assembler-times "0xf000001\[\t \]+\[^\n\]*btt_info" 1 } } */
+
+/* Function entries should have offset and size of 0 at compile time.  */
+/* { dg-final { scan-assembler-times "0\[\t \]+\[^\n\]*bts_offset" 3 } } */
+/* { dg-final { scan-assembler-times "0\[\t \]+\[^\n\]*bts_size" 3 } } */
+
+extern int foo (int a) __attribute__((section(".foo_sec")));
+
+
+extern int bar (int b) __attribute__((section(".bar_sec")));
+extern void chacha (void) __attribute__((section(".bar_sec")));
+
+__attribute__((section(".foo_sec")))
+void baz (int *x)
+{
+  chacha ();
+
+  *x = foo (bar (*x));
+}
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c b/gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c
new file mode 100644
index 00000000000..48a946ab14b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c
@@ -0,0 +1,19 @@
+/* Test BTF extern linkage for functions.
+
+   We expect to see one BTF_KIND_FUNC type with global linkage (foo), and
+   one BTF_KIND_FUNC type with extern linkage (extfunc).  */
+
+/* { dg-do compile } */
+/* { dg-options "-O0 -gbtf -dA" } */
+
+/* { dg-final { scan-assembler-times "btt_info: kind=12, kflag=0, linkage=2" 1 } } */
+/* { dg-final { scan-assembler-times "btt_info: kind=12, kflag=0, linkage=1" 1 } } */
+
+extern int extfunc(int a, int b);
+
+int foo (int x) {
+
+  int y = extfunc (x, x+1);
+
+  return y;
+}
diff --git a/include/btf.h b/include/btf.h
index da621353aa1..2f8f6f68b27 100644
--- a/include/btf.h
+++ b/include/btf.h
@@ -178,6 +178,15 @@ struct btf_param
   uint32_t type;	/* Type of parameter.  */
 };
 
+/* BTF_KIND_FUNC records encode linkage information in the VLEN bits
+   of the type record.  These are the supported values.  */
+enum btf_func_linkage
+{
+  BTF_FUNC_STATIC = 0,
+  BTF_FUNC_GLOBAL = 1,
+  BTF_FUNC_EXTERN = 2,
+};
+
 /* BTF_KIND_VAR records encode linkage information in a single
    trailing struct btf_var.  These are the supported values.  */
 enum btf_var_linkage
@@ -195,12 +204,13 @@ struct btf_var
 };
 
 /* BTF_KIND_DATASEC is followed by VLEN struct btf_var_secinfo entries,
-   which describe all BTF_KIND_VAR types contained in the section.  */
+   which describe all BTF_KIND_VAR or extern BTF_KIND_FUNC types contained
+   in the section.  */
 struct btf_var_secinfo
 {
-  uint32_t type;	/* Type of variable.  */
-  uint32_t offset;	/* In-section offset of variable (in bytes).  */
-  uint32_t size;	/* Size (in bytes) of variable.  */
+  uint32_t type;	/* Type of BTF_KIND_VAR or BTF_KIND_FUNC item.  */
+  uint32_t offset;	/* In-section offset (in bytes) of item.  */
+  uint32_t size;	/* Size (in bytes) of item.  */
 };
 
 /* BTF_KIND_ENUM64 is followed by VLEN struct btf_enum64 entries,
-- 
2.38.1

Re: [PATCH v2 0/3] btf: fix BTF for extern items [PR106773]

[Indu Bhagat]

On 12/13/22 10:44, David Faust wrote:
> [Changes from v1:
>   - Remove #defines for LINKAGE_* values, instead mirror enums from
>     linux/btf.h to include/btf.h and use those.
>   - Fix BTF generation for extern variable with both non-defining and
>     defining decls in the same CU. Add a test for this.
>   - Update several comments per review feedback. ]
> 
> Hi,
> 
> This series fixes the issues reported in target/PR106773. I decided to
> split it into three commits, as there are ultimately three distinct
> issues and fixes. See each patch for details.
> 
> Tested on bpf-unknown-none and x86_64-linux-gnu, no known regressions.
> 
> OK to push?
> Thanks.
> 

Hi David,

LGTM.

Thanks

> David Faust (3):
>    btf: add 'extern' linkage for variables [PR106773]
>    btf: fix 'extern const void' variables [PR106773]
>    btf: correct generation for extern funcs [PR106773]
> 
>   gcc/btfout.cc                                 | 184 +++++++++++++-----
>   .../gcc.dg/debug/btf/btf-datasec-2.c          |  28 +++
>   .../gcc.dg/debug/btf/btf-function-6.c         |  19 ++
>   gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c |  25 +++
>   .../gcc.dg/debug/btf/btf-variables-4.c        |  24 +++
>   .../gcc.dg/debug/btf/btf-variables-5.c        |  19 ++
>   include/btf.h                                 |  29 ++-
>   7 files changed, 276 insertions(+), 52 deletions(-)
>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-datasec-2.c
>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-function-6.c
>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-pr106773.c
>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-4.c
>   create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-variables-5.c
>