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506da42e9f
The crash utility uses RTLD_NOW|RTLD_GLOBAL flags of dlopen() to load an extension. RTDL_GLOBAL will make symbols defined by the shared object available for symbol resolution of subsequently loaded shared objects. So symbols in subsequently loaded extensions are overwritten by the former loaded one with the same name. This can cause unexpected behaviors when loading two extension modules that have a symbol with the same name. For example, we can reproduce a segmentation violation by loading the current trace.so extension module with two different names. This patch changes functions within extensions/echo.c to be static and documents the issue in code comments, for extensions developers who takes echo.c as reference. Signed-off-by: Tao Liu <ltao@redhat.com> Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
117 lines
3.5 KiB
C
117 lines
3.5 KiB
C
/* echo.c - simple example of a crash extension
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*
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* Copyright (C) 2001, 2002 Mission Critical Linux, Inc.
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* Copyright (C) 2002-2005, 2007, 2013 David Anderson
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* Copyright (C) 2002-2005, 2007, 2013 Red Hat, Inc. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#include "defs.h" /* From the crash source top-level directory */
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static void echo_init(void); /* constructor function */
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static void echo_fini(void); /* destructor function (optional) */
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static void cmd_echo(void); /* Declare the commands and their help data. */
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static char *help_echo[];
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/*
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* Please making the functions and global variables static within your
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* extension if you don't want to make them visiable to subsequently
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* loaded extensions. Otherwise, non-static symbols within 2 extensions
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* that have the same name can cause confliction.
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*/
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static struct command_table_entry command_table[] = {
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{ "echo", cmd_echo, help_echo, 0}, /* One or more commands, */
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{ NULL }, /* terminated by NULL, */
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};
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static void __attribute__((constructor))
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echo_init(void) /* Register the command set. */
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{
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register_extension(command_table);
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}
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/*
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* This function is called if the shared object is unloaded.
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* If desired, perform any cleanups here.
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*/
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static void __attribute__((destructor))
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echo_fini(void) { }
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/*
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* Arguments are passed to the command functions in the global args[argcnt]
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* array. See getopt(3) for info on dash arguments. Check out defs.h and
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* other crash commands for usage of the myriad of utility routines available
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* to accomplish what your task.
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*/
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static void
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cmd_echo(void)
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{
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int c;
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while ((c = getopt(argcnt, args, "")) != EOF) {
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switch(c)
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{
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default:
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argerrs++;
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break;
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}
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}
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if (argerrs)
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cmd_usage(pc->curcmd, SYNOPSIS);
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while (args[optind])
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fprintf(fp, "%s ", args[optind++]);
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fprintf(fp, "\n");
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}
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/*
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* The optional help data is simply an array of strings in a defined format.
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* For example, the "help echo" command will use the help_echo[] string
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* array below to create a help page that looks like this:
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*
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* NAME
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* echo - echoes back its arguments
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*
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* SYNOPSIS
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* echo arg ...
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*
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* DESCRIPTION
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* This command simply echoes back its arguments.
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*
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* EXAMPLE
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* Echo back all command arguments:
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*
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* crash> echo hello, world
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* hello, world
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*
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*/
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static char *help_echo[] = {
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"echo", /* command name */
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"echoes back its arguments", /* short description */
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"arg ...", /* argument synopsis, or " " if none */
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" This command simply echoes back its arguments.",
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"\nEXAMPLE",
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" Echo back all command arguments:\n",
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" crash> echo hello, world",
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" hello, world",
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NULL
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};
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