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samitolvanenmasahir0y
samitolvanen
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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 <[email protected]> Reviewed-by: Petr Pavlu <[email protected]> Signed-off-by: Masahiro Yamada <[email protected]>
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‎MAINTAINERS

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@@ -9550,6 +9550,13 @@ W: https://linuxtv.org
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T: git git://linuxtv.org/media.git
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F: drivers/media/radio/radio-gemtek*
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GENDWARFKSYMS
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M: Sami Tolvanen <[email protected]>
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L: [email protected]
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L: [email protected]
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S: Maintained
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F: scripts/gendwarfksyms/
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GENERIC ARCHITECTURE TOPOLOGY
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M: Sudeep Holla <[email protected]>
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L: [email protected]

‎kernel/module/Kconfig

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@@ -169,6 +169,14 @@ config MODVERSIONS
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make them incompatible with the kernel you are running. If
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unsure, say N.
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config GENDWARFKSYMS
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bool "gendwarfksyms (from debugging information)"
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depends on DEBUG_INFO
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# Requires full debugging information, split DWARF not supported.
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depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT
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# Requires ELF object files.
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depends on !LTO
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config ASM_MODVERSIONS
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bool
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default HAVE_ASM_MODVERSIONS && MODVERSIONS

‎scripts/Makefile

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@@ -54,6 +54,7 @@ targets += module.lds
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subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
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subdir-$(CONFIG_MODVERSIONS) += genksyms
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subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
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subdir-$(CONFIG_SECURITY_SELINUX) += selinux
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subdir-$(CONFIG_SECURITY_IPE) += ipe
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‎scripts/gendwarfksyms/.gitignore

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# SPDX-License-Identifier: GPL-2.0
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/gendwarfksyms

‎scripts/gendwarfksyms/Makefile

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# SPDX-License-Identifier: GPL-2.0
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hostprogs-always-y += gendwarfksyms
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gendwarfksyms-objs += gendwarfksyms.o
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gendwarfksyms-objs += dwarf.o
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gendwarfksyms-objs += symbols.o
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HOSTLDLIBS_gendwarfksyms := -ldw -lelf

‎scripts/gendwarfksyms/dwarf.c

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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2024 Google LLC
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*/
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#include "gendwarfksyms.h"
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static bool get_ref_die_attr(Dwarf_Die *die, unsigned int id, Dwarf_Die *value)
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{
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Dwarf_Attribute da;
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/* dwarf_formref_die returns a pointer instead of an error value. */
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return dwarf_attr(die, id, &da) && dwarf_formref_die(&da, value);
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}
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#define DEFINE_GET_STRING_ATTR(attr) \
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static const char *get_##attr##_attr(Dwarf_Die *die) \
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{ \
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Dwarf_Attribute da; \
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if (dwarf_attr(die, DW_AT_##attr, &da)) \
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return dwarf_formstring(&da); \
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return NULL; \
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}
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DEFINE_GET_STRING_ATTR(name)
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DEFINE_GET_STRING_ATTR(linkage_name)
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static const char *get_symbol_name(Dwarf_Die *die)
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{
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const char *name;
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/* rustc uses DW_AT_linkage_name for exported symbols */
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name = get_linkage_name_attr(die);
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if (!name)
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name = get_name_attr(die);
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return name;
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}
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static bool match_export_symbol(struct state *state, Dwarf_Die *die)
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{
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Dwarf_Die *source = die;
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Dwarf_Die origin;
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/* If the DIE has an abstract origin, use it for type information. */
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if (get_ref_die_attr(die, DW_AT_abstract_origin, &origin))
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source = &origin;
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state->sym = symbol_get(get_symbol_name(die));
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/* Look up using the origin name if there are no matches. */
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if (!state->sym && source != die)
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state->sym = symbol_get(get_symbol_name(source));
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state->die = *source;
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return !!state->sym;
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}
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/*
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* Type string processing
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*/
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static void process(const char *s)
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{
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s = s ?: "<null>";
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if (dump_dies)
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fputs(s, stderr);
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}
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bool match_all(Dwarf_Die *die)
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{
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return true;
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}
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int process_die_container(struct state *state, Dwarf_Die *die,
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die_callback_t func, die_match_callback_t match)
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{
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Dwarf_Die current;
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int res;
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res = checkp(dwarf_child(die, &current));
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while (!res) {
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if (match(&current)) {
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/* <0 = error, 0 = continue, >0 = stop */
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res = checkp(func(state, &current));
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if (res)
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return res;
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}
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res = checkp(dwarf_siblingof(&current, &current));
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}
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return 0;
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}
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/*
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* Exported symbol processing
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*/
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static void process_symbol(struct state *state, Dwarf_Die *die,
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die_callback_t process_func)
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{
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debug("%s", state->sym->name);
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check(process_func(state, die));
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if (dump_dies)
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fputs("\n", stderr);
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}
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static int __process_subprogram(struct state *state, Dwarf_Die *die)
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{
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process("subprogram");
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return 0;
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}
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static void process_subprogram(struct state *state, Dwarf_Die *die)
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{
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process_symbol(state, die, __process_subprogram);
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}
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static int __process_variable(struct state *state, Dwarf_Die *die)
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{
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process("variable ");
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return 0;
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}
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static void process_variable(struct state *state, Dwarf_Die *die)
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{
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process_symbol(state, die, __process_variable);
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}
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static int process_exported_symbols(struct state *unused, Dwarf_Die *die)
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{
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int tag = dwarf_tag(die);
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switch (tag) {
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/* Possible containers of exported symbols */
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case DW_TAG_namespace:
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case DW_TAG_class_type:
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case DW_TAG_structure_type:
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return check(process_die_container(
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NULL, die, process_exported_symbols, match_all));
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/* Possible exported symbols */
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case DW_TAG_subprogram:
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case DW_TAG_variable: {
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struct state state;
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if (!match_export_symbol(&state, die))
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return 0;
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if (tag == DW_TAG_subprogram)
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process_subprogram(&state, &state.die);
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else
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process_variable(&state, &state.die);
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return 0;
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}
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default:
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return 0;
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}
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}
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void process_cu(Dwarf_Die *cudie)
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{
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check(process_die_container(NULL, cudie, process_exported_symbols,
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match_all));
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}

‎scripts/gendwarfksyms/gendwarfksyms.c

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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2024 Google LLC
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*/
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#include <fcntl.h>
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#include <getopt.h>
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#include <errno.h>
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#include <stdarg.h>
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#include <string.h>
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#include <unistd.h>
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#include "gendwarfksyms.h"
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/*
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* Options
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*/
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/* Print debugging information to stderr */
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int debug;
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/* Dump DIE contents */
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int dump_dies;
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static void usage(void)
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{
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fputs("Usage: gendwarfksyms [options] elf-object-file ... < symbol-list\n\n"
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"Options:\n"
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" -d, --debug Print debugging information\n"
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" --dump-dies Dump DWARF DIE contents\n"
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" -h, --help Print this message\n"
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"\n",
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stderr);
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}
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static int process_module(Dwfl_Module *mod, void **userdata, const char *name,
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Dwarf_Addr base, void *arg)
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{
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Dwarf_Addr dwbias;
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Dwarf_Die cudie;
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Dwarf_CU *cu = NULL;
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Dwarf *dbg;
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int res;
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debug("%s", name);
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dbg = dwfl_module_getdwarf(mod, &dwbias);
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do {
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res = dwarf_get_units(dbg, cu, &cu, NULL, NULL, &cudie, NULL);
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if (res < 0)
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error("dwarf_get_units failed: no debugging information?");
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if (res == 1)
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break; /* No more units */
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process_cu(&cudie);
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} while (cu);
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return DWARF_CB_OK;
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}
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static const Dwfl_Callbacks callbacks = {
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.section_address = dwfl_offline_section_address,
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.find_debuginfo = dwfl_standard_find_debuginfo,
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};
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int main(int argc, char **argv)
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{
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unsigned int n;
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int opt;
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static const struct option opts[] = {
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{ "debug", 0, NULL, 'd' },
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{ "dump-dies", 0, &dump_dies, 1 },
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{ "help", 0, NULL, 'h' },
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{ 0, 0, NULL, 0 }
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};
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while ((opt = getopt_long(argc, argv, "dh", opts, NULL)) != EOF) {
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switch (opt) {
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case 0:
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break;
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case 'd':
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debug = 1;
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break;
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case 'h':
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usage();
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return 0;
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default:
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usage();
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return 1;
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}
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}
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if (optind >= argc) {
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usage();
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error("no input files?");
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}
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symbol_read_exports(stdin);
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for (n = optind; n < argc; n++) {
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Dwfl *dwfl;
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int fd;
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fd = open(argv[n], O_RDONLY);
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if (fd == -1)
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error("open failed for '%s': %s", argv[n],
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strerror(errno));
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dwfl = dwfl_begin(&callbacks);
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if (!dwfl)
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error("dwfl_begin failed for '%s': %s", argv[n],
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dwarf_errmsg(-1));
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if (!dwfl_report_offline(dwfl, argv[n], argv[n], fd))
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error("dwfl_report_offline failed for '%s': %s",
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argv[n], dwarf_errmsg(-1));
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dwfl_report_end(dwfl, NULL, NULL);
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if (dwfl_getmodules(dwfl, &process_module, NULL, 0))
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error("dwfl_getmodules failed for '%s'", argv[n]);
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dwfl_end(dwfl);
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}
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symbol_free();
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return 0;
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}

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