[PATCH v4 04/19] gendwarfksyms: Expand base_type

Sami Tolvanen
2024-10-08T18:38:44Z

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;
}