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Re: 'make test' error

From: Bruno Haible
Subject: Re: 'make test' error
Date: Sat, 6 Dec 2008 16:54:54 +0100
User-agent: KMail/1.9.9

Eric Blake wrote:
> In other words, it seems like we should consider
> modifying the contract of c-stack to state that the application should not
> modify SIGBUS handlers.

Yes, right. I'm adding this comment:

2008-12-06  Bruno Haible  <address@hidden>

        * lib/c-stack.h (c_stack_action): Clarify possible side effects.
        Suggested by Eric Blake.

--- lib/c-stack.h.orig  2008-12-06 16:50:18.000000000 +0100
+++ lib/c-stack.h       2008-12-06 16:49:15.000000000 +0100
@@ -36,6 +36,9 @@
    ACTION must be async-signal-safe.  ACTION together with its callees
    must not require more than SIGSTKSZ bytes of stack space.  Also,
    ACTION should not call longjmp, because this implementation does
-   not guarantee that it is safe to return to the original stack.  */
+   not guarantee that it is safe to return to the original stack.
+   This function may install a handler for the SIGSEGV signal or for the SIGBUS
+   signal or exercise other system dependent exception handling APIs.  */
 extern int c_stack_action (void (* /*action*/) (int));

> On looking at libsigsegv, it looks like it also conditionally installs a
> SIGBUS handler.  Which means we found a bug in m4 1.4.12: if you are using
> libsigsegv, and on a platform like MacOS, then my installation of a SIGBUS
> handler overwrites the libsigsegv handler, and you lose out on stack
> overflow detection.

That might actually happen on *BSD systems. On MacOS X, this bug will not
happen, because libsigsegv installs a Mach exception handler. This handler
installed by libsigsegv will be invoked before the SIGBUS handler installed
by m4 will be invoked.

> Also, if we modify the c-stack contract to always take care of SIGBUS, is
> there a way to make it detect whether libsigsegv installed a SIBGUS handler?

You can detect it by calling sigaction(SIGBUS,NULL,&curr_handler).


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