On 07/14/11 17:25, Pádraig Brady wrote:
> I'm not sure about defining these to 0 in gnulib.
> That will silently ignore the intent of a program on certain platforms.
> Wouldn't it be better to fail to compile so that each program then does:
>
> #ifndef SA_RESETHAND
> /* do something else */
> #endif
Well, as a matter of style, I prefer this:
if (! SA_RESETHAND)
do_something_else ();
as that's much more likely to detect bitrot in the "do something else"
part. (Of course this is all assuming the application writer knows
about platforms where SA_RESETHAND isn't implemented.)
On NonStop, if you invoke signal(), it uses the SA_RESETHAND semantics
(POSIX allows this). Conversely, if you invoke sigaction(), NonStop
always behaves as if SA_RESTART and SA_RESETHAND are zero, i.e., it
doesn't support either feature with sigaction.
I just now checked coreutils. Two programs use SA_RESETHAND. The
first (csplit) is clearly using it incorrectly, and won't work
properly on any host that implements SA_RESETHAND according to POSIX.
The second (dd) is using the above idiom already, that is, it is
assuming SA_RESETHAND is #defined to 0 on hosts that don't support it.
(It has some obsolete comments though, that need fixing.)
Conversely, the two programs that depend on SA_RESTART will
probably misbehave if a signal interrupts a system call on
NonStop. I see no easy fix for this, and I expect the gnulib
change may be the best we can do.
Here are a couple of patches that address the SA_RESETHAND problems
mentioned above. They assume the gnulib change. They fix the csplit
bug (and also allow it to work on NonStop, assuming the gnulib
change).
diff --git a/src/csplit.c b/src/csplit.c
index 438d888..4a0914e 100644
--- a/src/csplit.c
+++ b/src/csplit.c
@@ -225,6 +225,9 @@ static void
interrupt_handler (int sig)
{
delete_all_files (true);
+
+ signal (sig, SIG_DFL);
+
/* The signal has been reset to SIG_DFL, but blocked during this
handler. Force the default action of this signal once the
handler returns and the block is removed. */
@@ -1421,7 +1424,7 @@ main (int argc, char **argv)
act.sa_handler = interrupt_handler;
act.sa_mask = caught_signals;
- act.sa_flags = SA_NODEFER | SA_RESETHAND;
+ act.sa_flags = 0;
for (i = 0; i < nsigs; i++)
if (sigismember (&caught_signals, sig[i]))
diff --git a/src/dd.c b/src/dd.c
index 45aa9b9..c30c78a 100644
--- a/src/dd.c
+++ b/src/dd.c
@@ -45,7 +45,7 @@
proper_name ("Stuart Kemp")
/* Use SA_NOCLDSTOP as a proxy for whether the sigaction machinery is
- present. SA_NODEFER and SA_RESETHAND are XSI extensions. */
+ present. */
#ifndef SA_NOCLDSTOP
# define SA_NOCLDSTOP 0
# define sigprocmask(How, Set, Oset) /* empty */
@@ -726,9 +726,6 @@ install_signal_handlers (void)
if (sigismember (&caught_signals, SIGINT))
{
- /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER,
- but this is not true on Solaris 8 at least. It doesn't
- hurt to use SA_NODEFER here, so leave it in. */
act.sa_handler = interrupt_handler;
act.sa_flags = SA_NODEFER | SA_RESETHAND;
sigaction (SIGINT, &act, NULL);
