On 9/23/24 20:18, Sami Tolvanen wrote:
> 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 <samitolva...@google.com>
> ---
> kernel/module/Kconfig | 8 ++
> scripts/Makefile | 1 +
> scripts/gendwarfksyms/.gitignore | 2 +
> scripts/gendwarfksyms/Makefile | 8 ++
> scripts/gendwarfksyms/dwarf.c | 166 ++++++++++++++++++++++++++
> scripts/gendwarfksyms/gendwarfksyms.c | 132 ++++++++++++++++++++
> scripts/gendwarfksyms/gendwarfksyms.h | 97 +++++++++++++++
> scripts/gendwarfksyms/symbols.c | 82 +++++++++++++
> 8 files changed, 496 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
> create mode 100644 scripts/gendwarfksyms/symbols.c
>
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index ccdbd1bc12aa..c3a0172a909f 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 6bcda4b9d054..d7fec46d38c0 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
> subdir-$(CONFIG_SECURITY_IPE) += ipe
>
> diff --git a/scripts/gendwarfksyms/.gitignore
> b/scripts/gendwarfksyms/.gitignore
> new file mode 100644
> index 000000000000..0927f8d3cd96
> --- /dev/null
> +++ b/scripts/gendwarfksyms/.gitignore
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0
> +/gendwarfksyms
> diff --git a/scripts/gendwarfksyms/Makefile b/scripts/gendwarfksyms/Makefile
> new file mode 100644
> index 000000000000..9f8fec4fd39b
> --- /dev/null
> +++ b/scripts/gendwarfksyms/Makefile
> @@ -0,0 +1,8 @@
> +# SPDX-License-Identifier: GPL-2.0
> +hostprogs-always-y += gendwarfksyms
> +
> +gendwarfksyms-objs += gendwarfksyms.o
> +gendwarfksyms-objs += dwarf.o
> +gendwarfksyms-objs += symbols.o
> +
> +HOSTLDLIBS_gendwarfksyms := -ldw -lelf
> diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c
> new file mode 100644
> index 000000000000..81df3e2ad3ae
> --- /dev/null
> +++ b/scripts/gendwarfksyms/dwarf.c
> @@ -0,0 +1,166 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Google LLC
> + */
> +
> +#include "gendwarfksyms.h"
> +
> +static bool get_ref_die_attr(Dwarf_Die *die, unsigned int id, Dwarf_Die
> *value)
> +{
> + Dwarf_Attribute da;
> +
> + /* dwarf_formref_die returns a pointer instead of an error value. */
> + return dwarf_attr(die, id, &da) && dwarf_formref_die(&da, value);
> +}
> +
> +#define DEFINE_GET_STRING_ATTR(attr) \
> + static const char *get_##attr##_attr(Dwarf_Die *die) \
> + { \
> + Dwarf_Attribute da; \
> + if (dwarf_attr(die, DW_AT_##attr, &da)) \
> + return dwarf_formstring(&da); \
> + return NULL; \
> + }
> +
> +DEFINE_GET_STRING_ATTR(name)
> +DEFINE_GET_STRING_ATTR(linkage_name)
> +
> +static const char *get_symbol_name(Dwarf_Die *die)
> +{
> + const char *name;
> +
> + /* rustc uses DW_AT_linkage_name for exported symbols */
> + name = get_linkage_name_attr(die);
> + if (!name)
> + name = get_name_attr(die);
> +
> + return name;
> +}
> +
> +static bool match_export_symbol(struct state *state, Dwarf_Die *die)
> +{
> + Dwarf_Die *source = die;
> + Dwarf_Die origin;
> +
> + /* If the DIE has an abstract origin, use it for type information. */
> + if (get_ref_die_attr(die, DW_AT_abstract_origin, &origin))
> + source = &origin;
> +
> + state->sym = symbol_get(get_symbol_name(die));
> +
> + /* Look up using the origin name if there are no matches. */
> + if (!state->sym && source != die)
> + state->sym = symbol_get(get_symbol_name(source));
> +
> + state->die = *source;
> + return !!state->sym;
> +}
> +
> +/*
> + * Type string processing
> + */
> +static void process(const char *s)
> +{
> + s = s ?: "<null>";
> +
> + if (dump_dies)
> + fputs(s, stderr);
> +}
> +
> +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, ¤t));
> + while (!res) {
> + if (match(¤t)) {
> + /* <0 = error, 0 = continue, >0 = stop */
> + res = checkp(func(state, ¤t));
> + if (res)
> + return res;
> + }
> +
> + res = checkp(dwarf_siblingof(¤t, ¤t));
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Exported symbol processing
> + */
> +static void process_symbol(struct state *state, Dwarf_Die *die,
> + die_callback_t process_func)
> +{
> + debug("%s", state->sym->name);
> + check(process_func(state, die));
> + if (dump_dies)
> + fputs("\n", stderr);
> +}
> +
> +static int __process_subprogram(struct state *state, Dwarf_Die *die)
> +{
> + process("subprogram");
> + return 0;
> +}
> +
> +static void process_subprogram(struct state *state, Dwarf_Die *die)
> +{
> + process_symbol(state, die, __process_subprogram);
> +}
> +
> +static int __process_variable(struct state *state, Dwarf_Die *die)
> +{
> + process("variable ");
> + return 0;
> +}
> +
> +static void process_variable(struct state *state, Dwarf_Die *die)
> +{
> + process_symbol(state, die, __process_variable);
> +}
> +
> +static int process_exported_symbols(struct state *unused, 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(
> + NULL, die, process_exported_symbols, match_all));
> +
> + /* Possible exported symbols */
> + case DW_TAG_subprogram:
> + case DW_TAG_variable: {
> + struct state state;
> +
> + if (!match_export_symbol(&state, die))
> + return 0;
> +
> + if (tag == DW_TAG_subprogram)
> + process_subprogram(&state, &state.die);
> + else
> + process_variable(&state, &state.die);
> +
> + return 0;
> + }
> + default:
> + return 0;
> + }
> +}
> +
> +void process_cu(Dwarf_Die *cudie)
> +{
> + check(process_die_container(NULL, cudie, process_exported_symbols,
> + match_all));
> +}
> diff --git a/scripts/gendwarfksyms/gendwarfksyms.c
> b/scripts/gendwarfksyms/gendwarfksyms.c
> new file mode 100644
> index 000000000000..096a334fa5b3
> --- /dev/null
> +++ b/scripts/gendwarfksyms/gendwarfksyms.c
> @@ -0,0 +1,132 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Google LLC
> + */
> +
> +#include <fcntl.h>
> +#include <getopt.h>
> +#include <errno.h>
> +#include <stdarg.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include "gendwarfksyms.h"
> +
> +/*
> + * Options
> + */
> +
> +/* Print debugging information to stderr */
> +int debug;
> +/* Dump DIE contents */
> +int dump_dies;
> +
> +static void usage(void)
> +{
> + fputs("Usage: gendwarfksyms [options] elf-object-file ... <
> symbol-list\n\n"
> + "Options:\n"
> + " -d, --debug Print debugging information\n"
> + " --dump-dies Dump DWARF DIE contents\n"
> + " -h, --help Print this message\n"
> + "\n",
> + stderr);
> +}
> +
> +static int process_module(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?");
> + if (res == 1)
> + break; /* No more units */
> +
> + process_cu(&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, char **argv)
> +{
> + unsigned int n;
> + int opt;
> +
> + struct option opts[] = { { "debug", 0, NULL, 'd' },
> + { "dump-dies", 0, &dump_dies, 1 },
> + { "help", 0, NULL, 'h' },
> + { 0, 0, NULL, 0 } };
> +
> + while ((opt = getopt_long(argc, argv, "dh", opts, NULL)) != EOF) {
> + switch (opt) {
> + case 0:
> + break;
> + case 'd':
> + debug = 1;
> + break;
> + case 'h':
> + usage();
> + return 0;
> + default:
> + usage();
> + return 1;
> + }
> + }
> +
> + if (optind >= argc) {
> + usage();
> + error("no input files?");
> + }
> +
> + symbol_read_exports(stdin);
> +
> + for (n = optind; n < argc; n++) {
> + Dwfl *dwfl;
> + int fd;
> +
> + fd = open(argv[n], O_RDONLY);
> + if (fd == -1) {
> + error("open failed for '%s': %s", argv[n],
> + strerror(errno));
> + return -1;
> + }
> +
> + dwfl = dwfl_begin(&callbacks);
> + if (!dwfl) {
> + error("dwfl_begin failed for '%s': %s", argv[n],
> + dwarf_errmsg(-1));
> + return -1;
> + }
> +
> + if (!dwfl_report_offline(dwfl, argv[n], argv[n], fd)) {
> + error("dwfl_report_offline failed for '%s': %s",
> + argv[n], dwarf_errmsg(-1));
> + return -1;
> + }
> +
> + dwfl_report_end(dwfl, NULL, NULL);
> +
> + if (dwfl_getmodules(dwfl, &process_module, NULL, 0)) {
> + error("dwfl_getmodules failed for '%s'", argv[n]);
> + return -1;
> + }
Nit: The four error() calls don't need to be followed by 'return -1;'
since the function now calls exit(1).
> +
> + dwfl_end(dwfl);
> + }
> +
> + return 0;
> +}
> diff --git a/scripts/gendwarfksyms/gendwarfksyms.h
> b/scripts/gendwarfksyms/gendwarfksyms.h
> new file mode 100644
> index 000000000000..1a10d18f178e
> --- /dev/null
> +++ b/scripts/gendwarfksyms/gendwarfksyms.h
> @@ -0,0 +1,97 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2024 Google LLC
> + */
> +
> +#include <dwarf.h>
> +#include <elfutils/libdw.h>
> +#include <elfutils/libdwfl.h>
> +#include <inttypes.h>
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <string.h>
> +
> +#include <hash.h>
> +#include <hashtable.h>
> +#include <list.h>
> +#include <xalloc.h>
> +
> +#ifndef __GENDWARFKSYMS_H
> +#define __GENDWARFKSYMS_H
> +
> +/*
> + * Options -- in gendwarfksyms.c
> + */
> +extern int debug;
> +extern int dump_dies;
> +
> +/*
> + * 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, ...) \
> + do { \
> + __println("error: ", format, ##__VA_ARGS__); \
> + exit(1); \
> + } while (0)
> +
> +/*
> + * Error handling helpers
> + */
> +#define __check(expr, test) \
> + ({ \
> + int __res = expr; \
> + if (test) \
> + error("`%s` failed: %d", #expr, __res); \
> + __res; \
> + })
> +
> +/* Error == non-zero values */
> +#define check(expr) __check(expr, __res)
> +/* Error == negative values */
> +#define checkp(expr) __check(expr, __res < 0)
> +
> +/*
> + * symbols.c
> + */
> +
> +struct symbol {
> + const char *name;
> + struct hlist_node name_hash;
> +};
> +
> +typedef void (*symbol_callback_t)(struct symbol *, void *arg);
> +
> +void symbol_read_exports(FILE *file);
> +struct symbol *symbol_get(const char *name);
> +
> +/*
> + * dwarf.c
> + */
> +
> +struct state {
> + struct symbol *sym;
> + Dwarf_Die die;
> +};
> +
> +typedef int (*die_callback_t)(struct state *state, Dwarf_Die *die);
> +typedef bool (*die_match_callback_t)(Dwarf_Die *die);
> +bool match_all(Dwarf_Die *die);
> +
> +int process_die_container(struct state *state, Dwarf_Die *die,
> + die_callback_t func, die_match_callback_t match);
> +
> +void process_cu(Dwarf_Die *cudie);
> +
> +#endif /* __GENDWARFKSYMS_H */
> diff --git a/scripts/gendwarfksyms/symbols.c b/scripts/gendwarfksyms/symbols.c
> new file mode 100644
> index 000000000000..1809be93d18c
> --- /dev/null
> +++ b/scripts/gendwarfksyms/symbols.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Google LLC
> + */
> +
> +#include "gendwarfksyms.h"
> +
> +#define SYMBOL_HASH_BITS 15
> +static HASHTABLE_DEFINE(symbol_names, 1 << SYMBOL_HASH_BITS);
> +
> +static int for_each(const char *name, symbol_callback_t func, void *data)
> +{
> + struct hlist_node *tmp;
> + struct symbol *match;
> +
> + if (!name || !*name)
> + return 0;
> +
> + hash_for_each_possible_safe(symbol_names, match, tmp, name_hash,
> + hash_str(name)) {
> + if (strcmp(match->name, name))
> + continue;
> +
> + if (func)
> + func(match, data);
> +
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +static bool is_exported(const char *name)
> +{
> + return checkp(for_each(name, NULL, NULL)) > 0;
> +}
> +
> +void symbol_read_exports(FILE *file)
> +{
> + struct symbol *sym;
> + char *line = NULL;
> + char *name = NULL;
> + size_t size = 0;
> + int nsym = 0;
> +
> + while (getline(&line, &size, file) > 0) {
> + if (sscanf(line, "%ms\n", &name) != 1)
> + error("malformed input line: %s", line);
> +
> + if (is_exported(name)) {
> + /* Ignore duplicates */
> + free(name);
> + continue;
> + }
> +
> + sym = xcalloc(1, sizeof(struct symbol));
> + sym->name = name;
> +
> + hash_add(symbol_names, &sym->name_hash, hash_str(sym->name));
> + ++nsym;
> +
> + debug("%s", sym->name);
> + }
> +
> + free(line);
> + debug("%d exported symbols", nsym);
> +}
> +
> +static void get_symbol(struct symbol *sym, void *arg)
> +{
> + struct symbol **res = arg;
> +
> + *res = sym;
> +}
> +
> +struct symbol *symbol_get(const char *name)
> +{
> + struct symbol *sym = NULL;
> +
> + for_each(name, get_symbol, &sym);
> + return sym;
> +}
Nit: The code inconsistently checks for a potential error from the
function for_each(). Looking at the whole series, the value is checked
using checkp() in functions symbol_set_crc(), symbol_set_ptr(),
symbol_set_die(), is_exported(), but not in symbol_get() and
elf_set_symbol_addr(). It would be good to unify this, or perhaps even
make for_each() return an unsigned int to indicate it never fails?
Looks otherwise ok to me, feel free to add:
Reviewed-by: Petr Pavlu <petr.pa...@suse.com>
--
Thanks,
Petr
