Re: [Crash-utility] [PATCH 1/2] Let gdb get kernel module symbols info from crash

Date: Wed, 24 Aug 2022 12:10:33 +0800 From: Tao Liu <ltao(a)redhat.com&gt; To: crash-utility(a)redhat.com Subject: [Crash-utility] [PATCH 1/2] Let gdb get kernel module symbols info from crash Message-ID: <20220824041033.40559-1-ltao(a)redhat.com&gt; Content-Type: text/plain; charset="US-ASCII"; x-default=true Gdb will try to resolve an address to its corresponding symbol name such as when printing a structure. It works fine for kernel symbols, because gdb can find them through vmlinux. However as for kernel modules symbols, crash resolves them by dig into "struct module", which gdb don't know. As a results, gdb fails to translate an kernel modules address to it's symbolic name. For example we can reproduce the issue as follows. crash> timer .... 4331308176 336 ffff94ea24240860 ffffffffc03762c0 <estimation_timer> .... crash> sym 0xffffffffc03762c0 ffffffffc03762c0 (t) estimation_timer [ip_vs] Before patch: crash> timer_list ffff94ea24240860 struct timer_list { .... function = 0xffffffffc03762c0, .... } After patch: crash> timer_list ffff94ea24240860 struct timer_list { .... function = 0xffffffffc03762c0 <estimation_timer>, .... } In this patch, we add an interface for gdb, when gdb trying to build kernel module's address symbolic, the info can be get from crash. Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; --- defs.h | 2 ++ gdb-10.2.patch | 35 +++++++++++++++++++++++++++++++++-- gdb_interface.c | 12 ++++++++++++ 3 files changed, 47 insertions(+), 2 deletions(-) diff --git a/defs.h b/defs.h index 9d6d891..afdcf6c 100644 --- a/defs.h +++ b/defs.h @@ -4874,6 +4874,7 @@ extern "C" int patch_kernel_symbol(struct gnu_request *); struct syment *symbol_search(char *); int gdb_line_number_callback(ulong, ulong, ulong); int gdb_print_callback(ulong); +char *gdb_lookup_module_symbol(ulong, ulong *); extern "C" int same_file(char *, char *); #endif @@ -7284,6 +7285,7 @@ int gdb_pass_through(char *, FILE *, ulong); int gdb_readmem_callback(ulong, void *, int, int); int gdb_line_number_callback(ulong, ulong, ulong); int gdb_print_callback(ulong); +char *gdb_lookup_module_symbol(ulong, ulong *); void gdb_error_hook(void); void restore_gdb_sanity(void); int is_gdb_command(int, ulong); diff --git a/gdb-10.2.patch b/gdb-10.2.patch index f0034ed..d08e9ab 100644 --- a/gdb-10.2.patch +++ b/gdb-10.2.patch @@ -399,7 +399,38 @@ exit 0 if (build_address_symbolic (gdbarch, addr, do_demangle, false, &name, &offset, &filename, &line, &unmapped)) return 0; -@@ -1221,6 +1230,43 @@ print_command_1 (const char *args, int voidprint) +@@ -567,6 +576,10 @@ print_address_symbolic (struct gdbarch *gdbarch, CORE_ADDR addr, + + /* See valprint.h. */ + ++#ifdef CRASH_MERGE ++extern "C" char *gdb_lookup_module_symbol(unsigned long, unsigned long *); ++#endif ++ + int + build_address_symbolic (struct gdbarch *gdbarch, + CORE_ADDR addr, /* IN */ +@@ -673,7 +686,19 @@ build_address_symbolic (struct gdbarch *gdbarch, + } + } + if (symbol == NULL && msymbol.minsym == NULL) ++#ifdef CRASH_MERGE ++ { ++ char *name_ptr = gdb_lookup_module_symbol(addr, (unsigned long *)offset); ++ if (name_ptr) { ++ *name = name_ptr; ++ return 0; ++ } else { ++ return 1; ++ } ++ } ++#else + return 1; ++#endif + + /* If the nearest symbol is too far away, don't print anything symbolic. */ + +@@ -1221,6 +1246,43 @@ print_command_1 (const char *args, int voidprint) print_value (val, print_opts); }

/* See valprint.h. */ void -@@ -2855,6 +2901,12 @@ but no count or size letter (see \"x\" command)."), +@@ -2855,6 +2917,12 @@ but no count or size letter (see \"x\" command)."), c = add_com ("print", class_vars, print_command, print_help.c_str ()); set_cmd_completer_handle_brkchars (c, print_command_completer); add_com_alias ("p", "print", class_vars, 1); diff --git a/gdb_interface.c b/gdb_interface.c index 3a7fcc9..b14319c 100644 --- a/gdb_interface.c +++ b/gdb_interface.c @@ -935,6 +935,18 @@ gdb_print_callback(ulong addr) return IS_KVADDR(addr); } +char * +gdb_lookup_module_symbol(ulong addr, ulong *offset) +{ + struct syment *sp; + + if ((sp = value_search_module(addr, offset))) { + return sp->name; + } else { + return NULL; + } +} + /* * Used by gdb_interface() to catch gdb-related errors, if desired. */ -- 2.33.1