Message-ID: <20240815173903.4172139-22-samitolvanen@google.com>
Date: Thu, 15 Aug 2024 17:39:05 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Masahiro Yamada <masahiroy@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, Petr Pavlu <petr.pavlu@...e.com>, 
	Neal Gompa <neal@...pa.dev>, Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>, 
	Asahi Linux <asahi@...ts.linux.dev>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v2 01/19] tools: Add gendwarfksyms

Add a basic DWARF parser, which uses libdw to traverse the debugging
information in an object file and looks for functions and variables.
In follow-up patches, this will be expanded to produce symbol versions
for CONFIG_MODVERSIONS from DWARF.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 kernel/module/Kconfig                 |   8 ++
 scripts/Makefile                      |   1 +
 scripts/gendwarfksyms/.gitignore      |   2 +
 scripts/gendwarfksyms/Makefile        |   7 ++
 scripts/gendwarfksyms/dwarf.c         |  87 +++++++++++++++
 scripts/gendwarfksyms/gendwarfksyms.c | 146 ++++++++++++++++++++++++++
 scripts/gendwarfksyms/gendwarfksyms.h |  78 ++++++++++++++
 7 files changed, 329 insertions(+)
 create mode 100644 scripts/gendwarfksyms/.gitignore
 create mode 100644 scripts/gendwarfksyms/Makefile
 create mode 100644 scripts/gendwarfksyms/dwarf.c
 create mode 100644 scripts/gendwarfksyms/gendwarfksyms.c
 create mode 100644 scripts/gendwarfksyms/gendwarfksyms.h

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 4047b6d48255..a506d4ac660f 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -168,6 +168,14 @@ config MODVERSIONS
 	  make them incompatible with the kernel you are running.  If
 	  unsure, say N.
 
+config GENDWARFKSYMS
+	bool
+	depends on DEBUG_INFO
+	# Requires full debugging information, split DWARF not supported.
+	depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT
+	# Requires ELF object files.
+	depends on !LTO
+
 config ASM_MODVERSIONS
 	bool
 	default HAVE_ASM_MODVERSIONS && MODVERSIONS
diff --git a/scripts/Makefile b/scripts/Makefile
index dccef663ca82..2fd0199662e9 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -54,6 +54,7 @@ targets += module.lds
 
 subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
 subdir-$(CONFIG_MODVERSIONS) += genksyms
+subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
 subdir-$(CONFIG_SECURITY_SELINUX) += selinux
 
 # Let clean descend into subdirs
diff --git a/scripts/gendwarfksyms/.gitignore b/scripts/gendwarfksyms/.gitignore
new file mode 100644
index 000000000000..ab8c763b3afe
--- /dev/null
+++ b/scripts/gendwarfksyms/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/gendwarfksyms
diff --git a/scripts/gendwarfksyms/Makefile b/scripts/gendwarfksyms/Makefile
new file mode 100644
index 000000000000..c1389c161f9c
--- /dev/null
+++ b/scripts/gendwarfksyms/Makefile
@@ -0,0 +1,7 @@
+hostprogs-always-y += gendwarfksyms
+
+gendwarfksyms-objs += gendwarfksyms.o
+gendwarfksyms-objs += dwarf.o
+
+HOST_EXTRACFLAGS := -I $(srctree)/tools/include
+HOSTLDLIBS_gendwarfksyms := -ldw -lelf
diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c
new file mode 100644
index 000000000000..65a29d0bd8f4
--- /dev/null
+++ b/scripts/gendwarfksyms/dwarf.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 Google LLC
+ */
+
+#include "gendwarfksyms.h"
+
+/*
+ * Type string processing
+ */
+static int process(struct state *state, const char *s)
+{
+	s = s ?: "<null>";
+
+	if (debug)
+		fputs(s, stderr);
+
+	return 0;
+}
+
+bool match_all(Dwarf_Die *die)
+{
+	return true;
+}
+
+int process_die_container(struct state *state, Dwarf_Die *die,
+			  die_callback_t func, die_match_callback_t match)
+{
+	Dwarf_Die current;
+	int res;
+
+	res = checkp(dwarf_child(die, &current));
+	while (!res) {
+		if (match(&current))
+			check(func(state, &current));
+		res = checkp(dwarf_siblingof(&current, &current));
+	}
+
+	return 0;
+}
+
+/*
+ * Symbol processing
+ */
+static int process_subprogram(struct state *state, Dwarf_Die *die)
+{
+	return check(process(state, "subprogram;\n"));
+}
+
+static int process_variable(struct state *state, Dwarf_Die *die)
+{
+	return check(process(state, "variable;\n"));
+}
+
+static int process_exported_symbols(struct state *state, Dwarf_Die *die)
+{
+	int tag = dwarf_tag(die);
+
+	switch (tag) {
+	/* Possible containers of exported symbols */
+	case DW_TAG_namespace:
+	case DW_TAG_class_type:
+	case DW_TAG_structure_type:
+		return check(process_die_container(
+			state, die, process_exported_symbols, match_all));
+
+	/* Possible exported symbols */
+	case DW_TAG_subprogram:
+	case DW_TAG_variable:
+		if (tag == DW_TAG_subprogram)
+			check(process_subprogram(state, die));
+		else
+			check(process_variable(state, die));
+
+		return 0;
+	default:
+		return 0;
+	}
+}
+
+int process_module(Dwfl_Module *mod, Dwarf *dbg, Dwarf_Die *cudie)
+{
+	struct state state = { .mod = mod, .dbg = dbg };
+
+	return check(process_die_container(
+		&state, cudie, process_exported_symbols, match_all));
+}
diff --git a/scripts/gendwarfksyms/gendwarfksyms.c b/scripts/gendwarfksyms/gendwarfksyms.c
new file mode 100644
index 000000000000..27f2d6423c45
--- /dev/null
+++ b/scripts/gendwarfksyms/gendwarfksyms.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 Google LLC
+ */
+
+#include <fcntl.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+#include "gendwarfksyms.h"
+
+/*
+ * Options
+ */
+
+/* Print out debugging information to stderr */
+bool debug;
+
+static const struct {
+	const char *arg;
+	bool *flag;
+	const char **param;
+} options[] = {
+	{ "--debug", &debug, NULL },
+};
+
+static int usage(void)
+{
+	error("usage: gendwarfksyms [options] elf-object-file ...");
+	return -1;
+}
+
+static const char *object_files[MAX_INPUT_FILES];
+static unsigned int object_count;
+
+static int parse_options(int argc, const char **argv)
+{
+	for (int i = 1; i < argc; i++) {
+		bool flag = false;
+
+		for (int j = 0; j < ARRAY_SIZE(options); j++) {
+			if (strcmp(argv[i], options[j].arg))
+				continue;
+
+			*options[j].flag = true;
+
+			if (options[j].param) {
+				if (++i >= argc) {
+					error("%s needs an argument",
+					      options[j].arg);
+					return -1;
+				}
+
+				*options[j].param = argv[i];
+			}
+
+			flag = true;
+			break;
+		}
+
+		if (!flag)
+			object_files[object_count++] = argv[i];
+	}
+
+	return object_count ? 0 : -1;
+}
+
+static int process_modules(Dwfl_Module *mod, void **userdata, const char *name,
+			   Dwarf_Addr base, void *arg)
+{
+	Dwarf_Addr dwbias;
+	Dwarf_Die cudie;
+	Dwarf_CU *cu = NULL;
+	Dwarf *dbg;
+	int res;
+
+	debug("%s", name);
+	dbg = dwfl_module_getdwarf(mod, &dwbias);
+
+	do {
+		res = dwarf_get_units(dbg, cu, &cu, NULL, NULL, &cudie, NULL);
+		if (res < 0) {
+			error("dwarf_get_units failed: no debugging information?");
+			return -1;
+		} else if (res == 1) {
+			break; /* No more units */
+		}
+
+		check(process_module(mod, dbg, &cudie));
+	} while (cu);
+
+	return DWARF_CB_OK;
+}
+
+static const Dwfl_Callbacks callbacks = {
+	.section_address = dwfl_offline_section_address,
+	.find_debuginfo = dwfl_standard_find_debuginfo,
+};
+
+int main(int argc, const char **argv)
+{
+	unsigned int n;
+
+	if (parse_options(argc, argv) < 0)
+		return usage();
+
+	for (n = 0; n < object_count; n++) {
+		Dwfl *dwfl;
+		int fd;
+
+		fd = open(object_files[n], O_RDONLY);
+		if (fd == -1) {
+			error("open failed for '%s': %s", object_files[n],
+			      strerror(errno));
+			return -1;
+		}
+
+		dwfl = dwfl_begin(&callbacks);
+		if (!dwfl) {
+			error("dwfl_begin failed for '%s': %s", object_files[n],
+			      dwarf_errmsg(-1));
+			return -1;
+		}
+
+		if (!dwfl_report_offline(dwfl, object_files[n], object_files[n],
+					 fd)) {
+			error("dwfl_report_offline failed for '%s': %s",
+			      object_files[n], dwarf_errmsg(-1));
+			return -1;
+		}
+
+		dwfl_report_end(dwfl, NULL, NULL);
+
+		if (dwfl_getmodules(dwfl, &process_modules, NULL, 0)) {
+			error("dwfl_getmodules failed for '%s'",
+			      object_files[n]);
+			return -1;
+		}
+
+		dwfl_end(dwfl);
+		close(fd);
+	}
+
+	return 0;
+}
diff --git a/scripts/gendwarfksyms/gendwarfksyms.h b/scripts/gendwarfksyms/gendwarfksyms.h
new file mode 100644
index 000000000000..5ab7ce7d4efb
--- /dev/null
+++ b/scripts/gendwarfksyms/gendwarfksyms.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2024 Google LLC
+ */
+
+#include <dwarf.h>
+#include <elfutils/libdw.h>
+#include <elfutils/libdwfl.h>
+#include <linux/hashtable.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#ifndef __GENDWARFKSYMS_H
+#define __GENDWARFKSYMS_H
+
+/*
+ * Options -- in gendwarfksyms.c
+ */
+extern bool debug;
+
+#define MAX_INPUT_FILES 128
+
+/*
+ * Output helpers
+ */
+#define __PREFIX "gendwarfksyms: "
+#define __println(prefix, format, ...)                                \
+	fprintf(stderr, prefix __PREFIX "%s: " format "\n", __func__, \
+		##__VA_ARGS__)
+
+#define debug(format, ...)                                    \
+	do {                                                  \
+		if (debug)                                    \
+			__println("", format, ##__VA_ARGS__); \
+	} while (0)
+
+#define warn(format, ...) __println("warning: ", format, ##__VA_ARGS__)
+#define error(format, ...) __println("error: ", format, ##__VA_ARGS__)
+
+/*
+ * Error handling helpers
+ */
+#define __check(expr, test, rv)                                 \
+	({                                                      \
+		int __res = expr;                               \
+		if (test) {                                     \
+			error("`%s` failed: %d", #expr, __res); \
+			return rv;                              \
+		}                                               \
+		__res;                                          \
+	})
+
+/* Error == non-zero values */
+#define check(expr) __check(expr, __res, -1)
+/* Error == negative values */
+#define checkp(expr) __check(expr, __res < 0, __res)
+
+/*
+ * dwarf.c
+ */
+
+struct state {
+	Dwfl_Module *mod;
+	Dwarf *dbg;
+};
+
+typedef int (*die_callback_t)(struct state *state, Dwarf_Die *die);
+typedef bool (*die_match_callback_t)(Dwarf_Die *die);
+extern bool match_all(Dwarf_Die *die);
+
+extern int process_die_container(struct state *state, Dwarf_Die *die,
+				 die_callback_t func,
+				 die_match_callback_t match);
+
+extern int process_module(Dwfl_Module *mod, Dwarf *dbg, Dwarf_Die *cudie);
+
+#endif /* __GENDWARFKSYMS_H */
-- 
2.46.0.184.g6999bdac58-goog

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