Oracle Pro*C/OCI install handlers for SIGSEGV/SIGABRT and friends - why, and how to disable?

Question

When using Pro*C (a embedded SQL preprocessor from Oracle for C-Code) or OCI I noticed that the connect/init routine installs some signal handlers.

That means before a

EXEC SQL CONNECT :username IDENTIFIED BY :password USING :dbspec ;

or a

OCIEnvNlsCreate()

I can verify that for example those signals have following handlers:

No              NAME                Pointer   SA_SIGINFO   SIG_DFL   SIG_IGN
―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
 1            SIGHUP                  (nil)        false      true     false
 2            SIGINT                  (nil)        false      true     false
 3           SIGQUIT                  (nil)        false      true     false
 4            SIGILL                  (nil)        false      true     false
 5           SIGTRAP                  (nil)        false      true     false
 6           SIGABRT                  (nil)        false      true     false
 7            SIGBUS                  (nil)        false      true     false
 8            SIGFPE                  (nil)        false      true     false
 9           SIGKILL                  (nil)        false      true     false
10           SIGUSR1                  (nil)        false      true     false
11           SIGSEGV                  (nil)        false      true     false
12           SIGUSR2                  (nil)        false      true     false
13           SIGPIPE                  (nil)        false      true     false
14           SIGALRM                  (nil)        false      true     false

After the connect/init statement the table looks like:

No              NAME                Pointer   SA_SIGINFO   SIG_DFL   SIG_IGN
―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
 1            SIGHUP                  (nil)        false      true     false
 2            SIGINT         0x7eff9e60bdac         true     false     false
 3           SIGQUIT         0x7eff9ea17f9c         true     false     false
 4            SIGILL         0x7eff9ea17f9c         true     false     false
 5           SIGTRAP         0x7eff9ea17f9c         true     false     false
 6           SIGABRT         0x7eff9ea17f9c         true     false     false
 7            SIGBUS         0x7eff9ea17f9c         true     false     false
 8            SIGFPE         0x7eff9ea17f9c         true     false     false
 9           SIGKILL                  (nil)        false      true     false
10           SIGUSR1                  (nil)        false      true     false
11           SIGSEGV         0x7eff9ea17f9c         true     false     false
12           SIGUSR2                  (nil)        false      true     false
13           SIGPIPE                    0x1         true     false      true
14           SIGALRM                  (nil)        false      true     false

where 0x7eff9e60bdac denotes sslsshandler() and 0x7eff9ea17f9c denotes skgesig_sigactionHandler() - both symbols defined in libclntsh.so.11.1 - the Oracle runtime library.

I am concerned about those Oracle signal handlers because it seems that they introduce quite some non-deterministic behaviour. That means depending on the OS, hardware and kind of segfault/abort I've observed following behaviour:

• an ugly stacktrace that does not contain much useful information
• direct program exit with exit-status 1 - without any core file writing and no error message
• direct program exit with exit-status 0 (sic!)

Especially the last behaviour is grotesque.

Thus, I am interested in:

• the motivation - why are those signal handlers installed by Oracle?
• how to disable them? - at least for signals that yield a core file by default - because for my use-case I want a core under those circumstances (during development) or a reliable and informative exit status in production
• is it safe to overwrite the Oracle signal-handler via e.g. act.sa_handler = SIG_DFL; sigaction(SIGABRT, &act, 0); ?
• what are the disadvantages of resetting SIGABRT/SIGSEGV and friends to SIG_DFL after connect?

Essy

Best solution would be not to use buggy, non-thread-safe software like Oracle. – Mardellmarden

Answer 1

Signal handling and diagnostic framework considerations: the OCI diagnostic framework installs signal handlers that may impact any signal handling that you use in your application. You can disable OCI signal handling by setting

DIAG_SIGHANDLER_ENABLED=FALSE

in the sqlnet.ora file. Refer to "Fault Diagnosability in OCI" in Oracle Call Interface Programmer's Guide for information.

Please try to configure this environment variable in sqlnet.ora file

Unstained

Before changing the system-wide sqlnet.ora file - you can quickly test it locally like this: echo DIAG_SIGHANDLER_ENABLED=FALSE > sqlnet.ora; export TNS_ADMIN=$PWD – Essy

Answer 2

I would patch the Oracle .so file to replace the sigaction string with nosigactn and make a no-op function in your program called nosigactn with the same signature as sigaction.

Mardellmarden