Re: [Crash-utility] [PATCH] defs.h: fix breakage of compatibility of struct symbol_table_data for extension modules

Date: Wed, 8 Dec 2021 12:07:34 +0000 From: &quot;d.hatayama(a)fujitsu.com&quot; <d.hatayama(a)fujitsu.com&gt; To: &quot;crash-utility(a)redhat.com&quot; <crash-utility(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] defs.h: fix breakage of compatibility of struct symbol_table_data for extension modules Message-ID: <TYAPR01MB65079183F79B7F72B9486823956F9(a)TYAPR01MB6507.jpnprd01.prod.outlook.com&gt; Content-Type: text/plain; charset="iso-2022-jp" Commit 2fab8fbc0c4f1c4cbe889de4cead5f7457a19f77 (symbols: Implement install and remove operations for mod_symname_hash) added new member variable mod_symname_hash in the middle of struct symbol_table_data: diff --git a/defs.h b/defs.h index cbd45e5..bbdca79 100644 --- a/defs.h +++ b/defs.h @@ -2755,6 +2755,7 @@ struct symbol_table_data { double val_hash_searches; double val_hash_iterations; struct syment *symname_hash[SYMNAME_HASH]; + struct syment *mod_symname_hash[SYMNAME_HASH]; struct symbol_namespace kernel_namespace; struct syment *ext_module_symtable; struct syment *ext_module_symend; which breaks compatibility of struct symbol_table_data for extension modules. In general, new member variables must be added at the end of structures to maintain compatibility of data structures shared among extension modules.

For example, as the result, crash trace command results in segmentation fault: crash> trace show Segmentation fault (core dumped) in context of save_proc_kallsyms(): (gdb) bt #0 save_proc_kallsyms (fd=<optimized out>) at /usr/src/debug/crash-trace-command-3.0-4.el9.x86_64/trace.c:2234 #1 __trace_cmd_data_output (fd=<optimized out>) at /usr/src/debug/crash-trace-command-3.0-4.el9.x86_64/trace.c:2538 #2 0x00007f804e068dd5 in trace_cmd_data_output (fd=<optimized out>) at /usr/src/debug/crash-trace-command-3.0-4.el9.x86_64/trace.c:2588 #3 ftrace_show (argc=919286707, argv=<optimized out>, argv=<optimized out>) at /usr/src/debug/crash-trace-command-3.0-4.el9.x86_64/trace.c:1825 #4 0x00000000005010de in exec_command () at main.c:892 #5 0x0000000000500ed0 in main_loop () at main.c:839 #6 0x000000000085590d in captured_main (data=<optimized out>) at main.c:1284 #7 gdb_main (args=<optimized out>) at main.c:1313 #8 0x0000000000855965 in gdb_main_entry (argc=<optimized out>, argv=<optimized out>) at main.c:1338 #9 0x00000000005b3db7 in gdb_main_loop (argc=2, argv=0x7ffc5afb3ed8) at gdb_interface.c:81 #10 0x0000000000500b8d in main (argc=3, argv=0x7ffc5afb3ed8) at main.c:720 when referring to sp->name: static int save_proc_kallsyms(int fd) { int i; struct syment *sp; for (sp = st->symtable; sp < st->symend; sp++) tmp_fprintf("%lx %c %s\n", sp->value, sp->type, sp->name); for (i = 0; i < st->mods_installed; i++) { struct load_module *lm = &st->load_modules[i]; for (sp = lm->mod_symtable; sp <= lm->mod_symend; sp++) { => if (!strncmp(sp->name, "_MODULE_", strlen("_MODULE_"))) continue; where sp->name contains an odd address: (gdb) p sp->name Cannot access memory at address 0x20047 As seen above, save_proc_kallsyms() refers to st->load_modules and its position is behind the position where mod_symname_hash was added at: double val_hash_iterations; struct syment *symname_hash[SYMNAME_HASH]; struct syment *mod_symname_hash[SYMNAME_HASH]; struct symbol_namespace kernel_namespace; struct syment *ext_module_symtable; struct syment *ext_module_symend; long ext_module_symcnt; struct symbol_namespace ext_module_namespace; int mods_installed; struct load_module *current; struct load_module *load_modules; Signed-off-by: HATAYAMA Daisuke <d.hatayama(a)fujitsu.com&gt; --- defs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/defs.h b/defs.h index 7e2a16e..e9e8143 100644 --- a/defs.h +++ b/defs.h @@ -2753,7 +2753,6 @@ struct symbol_table_data { double val_hash_searches; double val_hash_iterations; struct syment *symname_hash[SYMNAME_HASH]; - struct syment *mod_symname_hash[SYMNAME_HASH]; struct symbol_namespace kernel_namespace; struct syment *ext_module_symtable; struct syment *ext_module_symend; @@ -2780,6 +2779,7 @@ struct symbol_table_data { ulong kaiser_init_vmlinux; int kernel_symbol_type; ulong linux_banner_vmlinux; + struct syment *mod_symname_hash[SYMNAME_HASH]; }; /* flags for st */ -- 2.31.1