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NetBSD/bin/sh/trap.c
kre 8a9a96192a PR bin/48875 (is related, and ameliorated, but not exactly "fixed") 
Import a whole set of tree evaluation enhancements from FreeBSD.

With these, before forking, the shell predicts (often) when all it will
have to do after forking (in the parent) is wait for the child and then
exit with the status from the child, and in such a case simply does not
fork, but rather allows the child to take over the parent's role.

This turns out to handle the particular test case from PR bin/48875 in
such a way that it works as hoped, rather than as it did (the delay there
was caused by an extra copy of the shell hanging around waiting for the
background child to complete ... and keeping the command substitution
stdout open, so the "real" parent had to wait in case more output appeared).

As part of doing this, redirection processing for compound commands gets
moved out of evalsubshell() and into a new evalredir(), which allows us
to properly handle errors occurring while performing those redirects,
and not mishandle (as in simply forget) fd's which had been moved out
of the way temporarily.

evaltree() has its degree of recursion reduced by making it loop to
handle the subsequent operation: that is instead of (for any binop
like ';' '&&' (etc)) where it used to
	evaltree(node->left);
	evaltree(node->right);
	return;
it now does (kind of)
	next = node;
	while ((node = next) != NULL) {
		next = NULL;

		if (node is a binary op) {
			evaltree(node->left);
			if appropriate /* if && test for success, etc */
				next = node->right;
			continue;
		}
		/* similar for loops, etc */
	}
which can be a good saving, as while the left side (now) tends to be
(usually) a simple (or simpleish) command, the right side can be many
commands (in a command sequence like a; b; c; d; ...  the node at the
top of the tree will now have "a" as its left node, and the tree for
b; c; d; ... as its right node - until now everything was evaluated
recursively so it made no difference, and the tree was constructed
the other way).

if/while/... statements are done similarly, recurse to evaluate the
condition, then if the (or one of the) body parts is to be evaluated,
set next to that, and loop (previously it recursed).

There is more to do in this area (particularly in the way that case
statements are processed - we can avoid recursion there as well) but
that can wait for another day.

While doing all of this we keep much better track of when the shell is
just going to exit once the current tree is evaluated (with a new
predicate at_eof() to tell us that we have, for sure, reached the end
of the input stream, that is, this shell will, for certain, not be reading
more command input) and use that info to avoid unneeded forks.   For that
we also need another new predicate (have_traps()) to determine of there
are any caught traps which might occur - if there are, we need to remain
to (potentially) handle them, so these optimisations will not occur (to
make the issue in PR 48875 appear again, run the same code, but with a
trap set to execute some code when a signal (or EXIT) occurs - note that
the trap must be set in the appropriate level of sub-shell to have this
effect, any caught traps are cleared in a subshell whenever one is created).

There is still work to be done to handle traps properly, whatever
weirdness they do (some of which is related to some of this.)

These changes do not need man page updates, but 48875 does - an update
to sh.1 will be forthcoming once it is decided what it should say...

Once again, all the heavy lifting for this set of changes comes directly
(with thanks) from the FreeBSD shell.

XXX pullup-8 (but not very soon)
2018-08-19 23:50:27 +00:00

611 lines
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/* $NetBSD: trap.c,v 1.45 2018/08/19 23:50:27 kre Exp $ */
/*-
* Copyright (c) 1991, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Kenneth Almquist.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#)trap.c 8.5 (Berkeley) 6/5/95";
#else
__RCSID("$NetBSD: trap.c,v 1.45 2018/08/19 23:50:27 kre Exp $");
#endif
#endif /* not lint */
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include "shell.h"
#include "main.h"
#include "nodes.h" /* for other headers */
#include "eval.h"
#include "jobs.h"
#include "show.h"
#include "options.h"
#include "builtins.h"
#include "syntax.h"
#include "output.h"
#include "memalloc.h"
#include "error.h"
#include "trap.h"
#include "mystring.h"
#include "var.h"
/*
* Sigmode records the current value of the signal handlers for the various
* modes. A value of zero means that the current handler is not known.
* S_HARD_IGN indicates that the signal was ignored on entry to the shell,
*/
#define S_DFL 1 /* default signal handling (SIG_DFL) */
#define S_CATCH 2 /* signal is caught */
#define S_IGN 3 /* signal is ignored (SIG_IGN) */
#define S_HARD_IGN 4 /* signal is ignored permenantly */
#define S_RESET 5 /* temporary - to reset a hard ignored sig */
char *trap[NSIG]; /* trap handler commands */
MKINIT char sigmode[NSIG]; /* current value of signal */
static volatile char gotsig[NSIG];/* indicates specified signal received */
volatile int pendingsigs; /* indicates some signal received */
static int getsigaction(int, sig_t *);
STATIC const char *trap_signame(int);
/*
* return the signal number described by `p' (as a number or a name)
* or -1 if it isn't one
*/
static int
signame_to_signum(const char *p)
{
int i;
if (is_number(p))
return number(p);
if (strcasecmp(p, "exit") == 0 )
return 0;
if (strncasecmp(p, "sig", 3) == 0)
p += 3;
for (i = 0; i < NSIG; ++i)
if (strcasecmp (p, sys_signame[i]) == 0)
return i;
return -1;
}
/*
* return the name of a signal used by the "trap" command
*/
STATIC const char *
trap_signame(int signo)
{
static char nbuf[12];
const char *p = NULL;
if (signo == 0)
return "EXIT";
if (signo > 0 && signo < NSIG)
p = sys_signame[signo];
if (p != NULL)
return p;
(void)snprintf(nbuf, sizeof nbuf, "%d", signo);
return nbuf;
}
/*
* Print a list of valid signal names
*/
static void
printsignals(void)
{
int n;
out1str("EXIT ");
for (n = 1; n < NSIG; n++) {
out1fmt("%s", trap_signame(n));
if ((n == NSIG/2) || n == (NSIG - 1))
out1str("\n");
else
out1c(' ');
}
}
/*
* The trap builtin.
*/
int
trapcmd(int argc, char **argv)
{
char *action;
char **ap;
int signo;
int errs = 0;
int printonly = 0;
ap = argv + 1;
if (argc == 2 && strcmp(*ap, "-l") == 0) {
printsignals();
return 0;
}
if (argc == 2 && strcmp(*ap, "-") == 0) {
for (signo = 0; signo < NSIG; signo++) {
if (trap[signo] == NULL)
continue;
INTOFF;
ckfree(trap[signo]);
trap[signo] = NULL;
if (signo != 0)
setsignal(signo, 0);
INTON;
}
return 0;
}
if (argc >= 2 && strcmp(*ap, "-p") == 0) {
printonly = 1;
ap++;
argc--;
}
if (argc > 1 && strcmp(*ap, "--") == 0) {
argc--;
ap++;
}
if (argc <= 1) {
int count;
if (printonly) {
for (count = 0, signo = 0 ; signo < NSIG ; signo++)
if (trap[signo] == NULL) {
if (count == 0)
out1str("trap -- -");
out1fmt(" %s", trap_signame(signo));
/* oh! unlucky 13 */
if (++count >= 13) {
out1str("\n");
count = 0;
}
}
if (count)
out1str("\n");
}
for (count = 0, signo = 0 ; signo < NSIG ; signo++)
if (trap[signo] != NULL && trap[signo][0] == '\0') {
if (count == 0)
out1str("trap -- ''");
out1fmt(" %s", trap_signame(signo));
/*
* the prefix is 10 bytes, with 4 byte
* signal names (common) we have room in
* the 70 bytes left on a normal line for
* 70/(4+1) signals, that's 14, but to
* allow for the occasional longer sig name
* we output one less...
*/
if (++count >= 13) {
out1str("\n");
count = 0;
}
}
if (count)
out1str("\n");
for (signo = 0 ; signo < NSIG ; signo++)
if (trap[signo] != NULL && trap[signo][0] != '\0') {
out1str("trap -- ");
print_quoted(trap[signo]);
out1fmt(" %s\n", trap_signame(signo));
}
return 0;
}
action = NULL;
if (!printonly && !is_number(*ap)) {
if ((*ap)[0] == '-' && (*ap)[1] == '\0')
ap++; /* reset to default */
else
action = *ap++; /* can be '' for "ignore" */
argc--;
}
if (argc < 2) { /* there must be at least 1 condition */
out2str("Usage: trap [-l]\n"
" trap -p [condition ...]\n"
" trap action condition ...\n"
" trap N condition ...\n");
return 2;
}
while (*ap) {
signo = signame_to_signum(*ap);
if (signo < 0 || signo >= NSIG) {
/* This is not a fatal error, so sayeth posix */
outfmt(out2, "trap: '%s' bad condition\n", *ap);
errs = 1;
ap++;
continue;
}
ap++;
if (printonly) {
out1str("trap -- ");
if (trap[signo] == NULL)
out1str("-");
else
print_quoted(trap[signo]);
out1fmt(" %s\n", trap_signame(signo));
continue;
}
INTOFF;
if (action)
action = savestr(action);
if (trap[signo])
ckfree(trap[signo]);
trap[signo] = action;
if (signo != 0)
setsignal(signo, 0);
INTON;
}
return errs;
}
/*
* Clear traps on a fork or vfork.
* Takes one arg vfork, to tell it to not be destructive of
* the parents variables.
*/
void
clear_traps(int vforked)
{
char **tp;
for (tp = trap ; tp < &trap[NSIG] ; tp++) {
if (*tp && **tp) { /* trap not NULL or SIG_IGN */
INTOFF;
if (!vforked) {
ckfree(*tp);
*tp = NULL;
}
if (tp != &trap[0])
setsignal(tp - trap, vforked);
INTON;
}
}
}
/*
* See if there are any defined traps
*/
int
have_traps(void)
{
char **tp;
for (tp = trap ; tp < &trap[NSIG] ; tp++)
if (*tp && **tp) /* trap not NULL or SIG_IGN */
return 1;
return 0;
}
/*
* Set the signal handler for the specified signal. The routine figures
* out what it should be set to.
*/
sig_t
setsignal(int signo, int vforked)
{
int action;
sig_t sigact = SIG_DFL, sig;
char *t, tsig;
if ((t = trap[signo]) == NULL)
action = S_DFL;
else if (*t != '\0')
action = S_CATCH;
else
action = S_IGN;
if (rootshell && !vforked && action == S_DFL) {
switch (signo) {
case SIGINT:
if (iflag || minusc || sflag == 0)
action = S_CATCH;
break;
case SIGQUIT:
#ifdef DEBUG
if (debug)
break;
#endif
/* FALLTHROUGH */
case SIGTERM:
if (iflag)
action = S_IGN;
break;
#if JOBS
case SIGTSTP:
case SIGTTOU:
if (mflag)
action = S_IGN;
break;
#endif
}
}
t = &sigmode[signo - 1];
tsig = *t;
if (tsig == 0) {
/*
* current setting unknown
*/
if (!getsigaction(signo, &sigact)) {
/*
* Pretend it worked; maybe we should give a warning
* here, but other shells don't. We don't alter
* sigmode, so that we retry every time.
*/
return 0;
}
if (sigact == SIG_IGN) {
/*
* POSIX 3.14.13 states that non-interactive shells
* should ignore trap commands for signals that were
* ignored upon entry, and leaves the behavior
* unspecified for interactive shells. On interactive
* shells, or if job control is on, and we have a job
* control related signal, we allow the trap to work.
*
* This change allows us to be POSIX compliant, and
* at the same time override the default behavior if
* we need to by setting the interactive flag.
*/
if ((mflag && (signo == SIGTSTP ||
signo == SIGTTIN || signo == SIGTTOU)) || iflag) {
tsig = S_IGN;
} else
tsig = S_HARD_IGN;
} else {
tsig = S_RESET; /* force to be set */
}
}
if (tsig == S_HARD_IGN || tsig == action)
return 0;
switch (action) {
case S_DFL: sigact = SIG_DFL; break;
case S_CATCH: sigact = onsig; break;
case S_IGN: sigact = SIG_IGN; break;
}
sig = signal(signo, sigact);
if (sig != SIG_ERR) {
sigset_t ss;
if (!vforked)
*t = action;
if (action == S_CATCH)
(void)siginterrupt(signo, 1);
/*
* If our parent accidentally blocked signals for
* us make sure we unblock them
*/
(void)sigemptyset(&ss);
(void)sigaddset(&ss, signo);
(void)sigprocmask(SIG_UNBLOCK, &ss, NULL);
}
return sig;
}
/*
* Return the current setting for sig w/o changing it.
*/
static int
getsigaction(int signo, sig_t *sigact)
{
struct sigaction sa;
if (sigaction(signo, (struct sigaction *)0, &sa) == -1)
return 0;
*sigact = (sig_t) sa.sa_handler;
return 1;
}
/*
* Ignore a signal.
*/
void
ignoresig(int signo, int vforked)
{
if (sigmode[signo - 1] != S_IGN && sigmode[signo - 1] != S_HARD_IGN) {
signal(signo, SIG_IGN);
}
if (!vforked)
sigmode[signo - 1] = S_HARD_IGN;
}
#ifdef mkinit
INCLUDE <signal.h>
INCLUDE "trap.h"
SHELLPROC {
char *sm;
clear_traps(0);
for (sm = sigmode ; sm < sigmode + NSIG ; sm++) {
if (*sm == S_IGN)
*sm = S_HARD_IGN;
}
}
#endif
/*
* Signal handler.
*/
void
onsig(int signo)
{
CTRACE(DBG_SIG, ("Signal %d, had: pending %d, gotsig[%d]=%d\n",
signo, pendingsigs, signo, gotsig[signo]));
signal(signo, onsig);
if (signo == SIGINT && trap[SIGINT] == NULL) {
onint();
return;
}
gotsig[signo] = 1;
pendingsigs++;
}
/*
* Called to execute a trap. Perhaps we should avoid entering new trap
* handlers while we are executing a trap handler.
*/
void
dotrap(void)
{
int i;
int savestatus;
char *tr;
for (;;) {
for (i = 1 ; ; i++) {
if (i >= NSIG) {
pendingsigs = 0;
return;
}
if (gotsig[i])
break;
}
gotsig[i] = 0;
savestatus=exitstatus;
CTRACE(DBG_TRAP|DBG_SIG, ("dotrap %d: \"%s\"\n", i,
trap[i] ? trap[i] : "-NULL-"));
if ((tr = trap[i]) != NULL) {
tr = savestr(tr); /* trap code may free trap[i] */
evalstring(tr, 0);
ckfree(tr);
}
exitstatus=savestatus;
}
}
int
lastsig(void)
{
int i;
for (i = NSIG; --i > 0; )
if (gotsig[i])
return i;
return SIGINT; /* XXX */
}
/*
* Controls whether the shell is interactive or not.
*/
void
setinteractive(int on)
{
static int is_interactive;
if (on == is_interactive)
return;
setsignal(SIGINT, 0);
setsignal(SIGQUIT, 0);
setsignal(SIGTERM, 0);
is_interactive = on;
}
/*
* Called to exit the shell.
*/
void
exitshell(int status)
{
struct jmploc loc1, loc2;
char *p;
CTRACE(DBG_ERRS|DBG_PROCS|DBG_CMDS|DBG_TRAP,
("pid %d, exitshell(%d)\n", getpid(), status));
if (setjmp(loc1.loc)) {
goto l1;
}
if (setjmp(loc2.loc)) {
goto l2;
}
handler = &loc1;
if ((p = trap[0]) != NULL && *p != '\0') {
trap[0] = NULL;
VTRACE(DBG_TRAP, ("exit trap: \"%s\"\n", p));
evalstring(p, 0);
}
l1: handler = &loc2; /* probably unnecessary */
flushall();
#if JOBS
setjobctl(0);
#endif
l2: _exit(status);
/* NOTREACHED */
}
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