Start making gendwarfksyms more useful by adding support for
expanding DW_TAG_base_type types and basic DWARF attributes.

Example:

  $ echo loops_per_jiffy | \
      scripts/gendwarfksyms/gendwarfksyms \
        --debug --dump-dies vmlinux.o
  ...
  gendwarfksyms: process_symbol: loops_per_jiffy
  variable base_type unsigned long byte_size(8) encoding(7)
  ...

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
---
 scripts/gendwarfksyms/dwarf.c | 159 ++++++++++++++++++++++++++++++++++
 1 file changed, 159 insertions(+)

diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c
index 81df3e2ad3ae..35fd1dfeeadc 100644
--- a/scripts/gendwarfksyms/dwarf.c
+++ b/scripts/gendwarfksyms/dwarf.c
@@ -3,8 +3,20 @@
  * Copyright (C) 2024 Google LLC
  */
 
+#include <stdarg.h>
 #include "gendwarfksyms.h"
 
+#define DEFINE_GET_ATTR(attr, type)                                    \
+	static bool get_##attr##_attr(Dwarf_Die *die, unsigned int id, \
+				      type *value)                     \
+	{                                                              \
+		Dwarf_Attribute da;                                    \
+		return dwarf_attr(die, id, &da) &&                     \
+		       !dwarf_form##attr(&da, value);                  \
+	}
+
+DEFINE_GET_ATTR(udata, Dwarf_Word)
+
 static bool get_ref_die_attr(Dwarf_Die *die, unsigned int id, Dwarf_Die *value)
 {
 	Dwarf_Attribute da;
@@ -67,6 +79,109 @@ static void process(const char *s)
 		fputs(s, stderr);
 }
 
+#define MAX_FMT_BUFFER_SIZE 128
+
+static void process_fmt(const char *fmt, ...)
+{
+	char buf[MAX_FMT_BUFFER_SIZE];
+	va_list args;
+
+	va_start(args, fmt);
+
+	if (checkp(vsnprintf(buf, sizeof(buf), fmt, args)) >= sizeof(buf))
+		error("vsnprintf overflow: increase MAX_FMT_BUFFER_SIZE");
+
+	process(buf);
+	va_end(args);
+}
+
+#define MAX_FQN_SIZE 64
+
+/* Get a fully qualified name from DWARF scopes */
+static char *get_fqn(Dwarf_Die *die)
+{
+	const char *list[MAX_FQN_SIZE];
+	Dwarf_Die *scopes = NULL;
+	bool has_name = false;
+	char *fqn = NULL;
+	char *p;
+	int count = 0;
+	int len = 0;
+	int res;
+	int i;
+
+	res = checkp(dwarf_getscopes_die(die, &scopes));
+	if (!res) {
+		list[count] = get_name_attr(die);
+
+		if (!list[count])
+			return NULL;
+
+		len += strlen(list[count]);
+		count++;
+
+		goto done;
+	}
+
+	for (i = res - 1; i >= 0 && count < MAX_FQN_SIZE; i--) {
+		if (dwarf_tag(&scopes[i]) == DW_TAG_compile_unit)
+			continue;
+
+		list[count] = get_name_attr(&scopes[i]);
+
+		if (list[count]) {
+			has_name = true;
+		} else {
+			list[count] = "<anonymous>";
+			has_name = false;
+		}
+
+		len += strlen(list[count]);
+		count++;
+
+		if (i > 0) {
+			list[count++] = "::";
+			len += 2;
+		}
+	}
+
+	free(scopes);
+
+	if (count == MAX_FQN_SIZE)
+		warn("increase MAX_FQN_SIZE: reached the maximum");
+
+	/* Consider the DIE unnamed if the last scope doesn't have a name */
+	if (!has_name)
+		return NULL;
+done:
+	fqn = xmalloc(len + 1);
+	*fqn = '\0';
+
+	p = fqn;
+	for (i = 0; i < count; i++)
+		p = stpcpy(p, list[i]);
+
+	return fqn;
+}
+
+static void process_fqn(Dwarf_Die *die)
+{
+	process(" ");
+	process(get_fqn(die) ?: "");
+}
+
+#define DEFINE_PROCESS_UDATA_ATTRIBUTE(attribute)                           \
+	static void process_##attribute##_attr(Dwarf_Die *die)              \
+	{                                                                   \
+		Dwarf_Word value;                                           \
+		if (get_udata_attr(die, DW_AT_##attribute, &value))         \
+			process_fmt(" " #attribute "(%" PRIu64 ")", value); \
+	}
+
+DEFINE_PROCESS_UDATA_ATTRIBUTE(alignment)
+DEFINE_PROCESS_UDATA_ATTRIBUTE(byte_size)
+DEFINE_PROCESS_UDATA_ATTRIBUTE(encoding)
+
 bool match_all(Dwarf_Die *die)
 {
 	return true;
@@ -93,6 +208,49 @@ int process_die_container(struct state *state, Dwarf_Die *die,
 	return 0;
 }
 
+static int process_type(struct state *state, Dwarf_Die *die);
+
+static void process_type_attr(struct state *state, Dwarf_Die *die)
+{
+	Dwarf_Die type;
+
+	if (get_ref_die_attr(die, DW_AT_type, &type)) {
+		check(process_type(state, &type));
+		return;
+	}
+
+	/* Compilers can omit DW_AT_type -- print out 'void' to clarify */
+	process("base_type void");
+}
+
+static void process_base_type(struct state *state, Dwarf_Die *die)
+{
+	process("base_type");
+	process_fqn(die);
+	process_byte_size_attr(die);
+	process_encoding_attr(die);
+	process_alignment_attr(die);
+}
+
+#define PROCESS_TYPE(type)                         \
+	case DW_TAG_##type##_type:                 \
+		process_##type##_type(state, die); \
+		break;
+
+static int process_type(struct state *state, Dwarf_Die *die)
+{
+	int tag = dwarf_tag(die);
+
+	switch (tag) {
+	PROCESS_TYPE(base)
+	default:
+		debug("unimplemented type: %x", tag);
+		break;
+	}
+
+	return 0;
+}
+
 /*
  * Exported symbol processing
  */
@@ -119,6 +277,7 @@ static void process_subprogram(struct state *state, Dwarf_Die *die)
 static int __process_variable(struct state *state, Dwarf_Die *die)
 {
 	process("variable ");
+	process_type_attr(state, die);
 	return 0;
 }
 
-- 
2.47.0.rc0.187.ge670bccf7e-goog