[Crash-utility] [PATCH 1/2] Change functions in extensions/echo.c to be static

[Tao Liu]

If a same extension(Eg: extensions/trace.so) with two different names are loaded by
"extend" command twice, it sometimes segfaults crash.

It's because crash uses RTLD_NOW|RTLD_GLOBAL flags of dlopen to load an extension.
RTDL_GLOBAL will make symbols defined by this 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 a same name.
Not only can it cause segfaults, but some other unexpected behaviours.

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 at redhat.com>
---
 extensions/echo.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/extensions/echo.c b/extensions/echo.c
index ff1e09a..f4bb88f 100644
--- a/extensions/echo.c
+++ b/extensions/echo.c
@@ -17,19 +17,25 @@
 
 #include "defs.h"      /* From the crash source top-level directory */
 
-void echo_init(void);    /* constructor function */
-void echo_fini(void);    /* destructor function (optional) */
+static void echo_init(void);    /* constructor function */
+static void echo_fini(void);    /* destructor function (optional) */
 
-void cmd_echo(void);     /* Declare the commands and their help data. */
-char *help_echo[];
+static void cmd_echo(void);     /* Declare the commands and their help data. */
+static char *help_echo[];
 
+/*
+ * Please making the functions and global variables static within your
+ * extension if you don't want to make them visiable to subsequently
+ * loaded extensions. Otherwise, non-static symbols within 2 extensions and
+ * have a same name can cause confliction.
+ */
 static struct command_table_entry command_table[] = {
         { "echo", cmd_echo, help_echo, 0},          /* One or more commands, */
         { NULL },                                     /* terminated by NULL, */
 };
 
 
-void __attribute__((constructor))
+static void __attribute__((constructor))
 echo_init(void) /* Register the command set. */
 { 
         register_extension(command_table);
@@ -39,7 +45,7 @@ echo_init(void) /* Register the command set. */
  *  This function is called if the shared object is unloaded. 
  *  If desired, perform any cleanups here. 
  */
-void __attribute__((destructor))
+static void __attribute__((destructor))
 echo_fini(void) { }
 
 
@@ -49,7 +55,7 @@ echo_fini(void) { }
  *  other crash commands for usage of the myriad of utility routines available
  *  to accomplish what your task.
  */
-void
+static void
 cmd_echo(void)
 {
         int c;
@@ -94,7 +100,7 @@ cmd_echo(void)
  *
  */
  
-char *help_echo[] = {
+static char *help_echo[] = {
         "echo",                        /* command name */
         "echoes back its arguments",   /* short description */
         "arg ...",                     /* argument synopsis, or " " if none */
-- 
2.29.2