klibc - Mar 2020 - [klibc:update-dash] dash: [SHELL] Optimize dash -c "command" to avoid a fork

Commit-ID:  a99e81cedacbfaed18e580455969667f2320de5e
Gitweb:    
http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=a99e81cedacbfaed18e580455969667f2320de5e
Author:     Herbert Xu <herbert at gondor.apana.org.au>
AuthorDate: Thu, 7 Jul 2011 13:58:48 +0800
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Sat, 28 Mar 2020 21:10:37 +0000

[klibc] dash: [SHELL] Optimize dash -c "command" to avoid a fork

[ dash commit ee5cbe9fd6bc02f31b4d955606288de36c3d4eab ]

On Sun, Apr 10, 2011 at 07:36:49AM +0000, Jonathan Nieder
wrote:
> From: Jilles Tjoelker <jilles at stack.nl>
> Date: Sat, 13 Jun 2009 16:17:45 -0500
>
> This change only affects strings passed to -c, when the -s option is
> not used.
>
> Use the EV_EXIT flag to inform the eval machinery that the string
> being passed is the entirety of input.  This way, a fork may be
> omitted in many special cases.
>
> If there are empty lines after the last command, the evalcmd will not
> see the end early enough and forks will not be omitted. The same thing
> seems to happen in bash.
>
> Example:
>   sh -c 'ps lT'
> No longer shows a shell process waiting for ps to finish.
>
> [jn: ported from FreeBSD SVN r194128.  Bugs are mine.]
>
> Signed-off-by: Jonathan Nieder <jrnieder at gmail.com>
Instead of detecting EOF using the input layer, I'm going to
use the parser instead.  In either case, we always have to read
ahead in order to complete the parsing of the previous node.
Therefore we always know whether there is more to come, except
in the case where we see a newline/semicolon or similar.

For the purposes of sh -c, this should be sufficient.

Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
[bwh: Update usr/dash/Kbuild for mktokens and parser.h changes, and
 README.dash to reflect that we now have this change]
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 usr/dash/.gitignore  |  1 +
 usr/dash/Kbuild      | 10 ++++++++--
 usr/dash/README.dash |  3 +--
 usr/dash/eval.c      |  6 +-----
 usr/dash/eval.h      |  4 ++++
 usr/dash/main.c      |  2 +-
 usr/dash/mktokens    |  9 ++++++---
 usr/dash/parser.c    |  5 +++--
 usr/dash/parser.h    |  8 ++++++++
 9 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/usr/dash/.gitignore b/usr/dash/.gitignore
index 480952fe..16a0cce9 100644
--- a/usr/dash/.gitignore
+++ b/usr/dash/.gitignore
@@ -11,3 +11,4 @@ sh
 sh.shared
 syntax.[ch]
 token.h
+token_vars.h
diff --git a/usr/dash/Kbuild b/usr/dash/Kbuild
index 23809a3a..f9c0b287 100644
--- a/usr/dash/Kbuild
+++ b/usr/dash/Kbuild
@@ -35,13 +35,19 @@ targets := static/sh static/sh.g shared/sh shared/sh.g
$(gen-o-files)
 # explicit dependency for all generated files
 $(addprefix $(obj)/, $(static/sh-y)): $(addprefix $(obj)/, $(gen-h-files))
 
-# Generate token.h
-targets += token.h
+$(obj)/mksyntax: $(obj)/token.h
+
+# Generate token{,_vars}.h
+targets += token.h token_vars.h
 quiet_cmd_mktokens = GEN     $@
       cmd_mktokens = (cd $(obj) && sh $(srctree)/$(src)/mktokens)
 $(obj)/token.h: $(src)/mktokens
 	$(call if_changed,mktokens)
 
+# side effect..
+$(obj)/token_vars.h: $(obj)/token.h
+	$(Q):
+
 # Generate builtins.def
 targets += builtins.def
 quiet_cmd_mkbuiltins_def = GEN     $@
diff --git a/usr/dash/README.dash b/usr/dash/README.dash
index f45d28be..3bb72799 100644
--- a/usr/dash/README.dash
+++ b/usr/dash/README.dash
@@ -2,8 +2,7 @@ This version of dash was obtained from
 
 git://git.kernel.org/pub/scm/utils/dash/dash.git
 
-It corresponds up to changeset 46abc8c6d8a5e9a5712bdc1312c0b6960eec65a4
-omitting ee5cbe9fd6bc02f31b4d955606288de36c3d4eab.
+It corresponds up to changeset 46abc8c6d8a5e9a5712bdc1312c0b6960eec65a4.
 
 Several changes have been made for klibc:
 
diff --git a/usr/dash/eval.c b/usr/dash/eval.c
index dd144948..e6f6cd5c 100644
--- a/usr/dash/eval.c
+++ b/usr/dash/eval.c
@@ -65,10 +65,6 @@
 #endif
 
 
-/* flags in argument to evaltree */
-#define EV_EXIT 01		/* exit after evaluating tree */
-#define EV_TESTED 02		/* exit status is checked; ignore -e flag */
-
 int evalskip;			/* set if we are skipping commands */
 STATIC int skipcount;		/* number of levels to skip */
 MKINIT int loopnest;		/* current loop nesting level */
@@ -169,7 +165,7 @@ evalstring(char *s, int flags)
 
 	status = 0;
 	while ((n = parsecmd(0)) != NEOF) {
-		evaltree(n, flags);
+		evaltree(n, flags & ~(parser_eof() ? 0 : EV_EXIT));
 		status = exitstatus;
 		popstackmark(&smark);
 		if (evalskip)
diff --git a/usr/dash/eval.h b/usr/dash/eval.h
index 5ccfa9f1..dc8acd2a 100644
--- a/usr/dash/eval.h
+++ b/usr/dash/eval.h
@@ -46,6 +46,10 @@ struct backcmd {		/* result of evalbackcmd */
 	struct job *jp;		/* job structure for command */
 };
 
+/* flags in argument to evaltree */
+#define EV_EXIT 01		/* exit after evaluating tree */
+#define EV_TESTED 02		/* exit status is checked; ignore -e flag */
+
 int evalstring(char *, int);
 union node;	/* BLETCH for ansi C */
 void evaltree(union node *, int);
diff --git a/usr/dash/main.c b/usr/dash/main.c
index 7df3c441..f79ad7dd 100644
--- a/usr/dash/main.c
+++ b/usr/dash/main.c
@@ -171,7 +171,7 @@ state2:
 state3:
 	state = 4;
 	if (minusc)
-		evalstring(minusc, 0);
+		evalstring(minusc, sflag ? 0 : EV_EXIT);
 
 	if (sflag || minusc == NULL) {
 state4:	/* XXX ??? - why isn't this before the "if" statement */
diff --git a/usr/dash/mktokens b/usr/dash/mktokens
index 43d76ce1..fa6ccf78 100644
--- a/usr/dash/mktokens
+++ b/usr/dash/mktokens
@@ -71,13 +71,16 @@ TEND	1	"}"
 nl=`wc -l /tmp/ka$$`
 exec > token.h
 awk '{print "#define " $1 " " NR-1}' /tmp/ka$$
+
+exec > token_vars.h
+
 echo '
 /* Array indicating which tokens mark the end of a list */
-const char tokendlist[] = {'
+static const char tokendlist[] = {'
 awk '{print "\t" $2 ","}' /tmp/ka$$
 echo '};
 
-const char *const tokname[] = {'
+static const char *const tokname[] = {'
 sed -e 's/"/\\"/g' \
     -e 's/[^	 ]*[	 ][	 ]*[^	 ]*[	 ][	 ]*\(.*\)/	"\1",/' \
     /tmp/ka$$
@@ -85,7 +88,7 @@ echo '};
 '
 sed 's/"//g' /tmp/ka$$ | awk '
 /TNOT/{print "#define KWDOFFSET " NR-1; print "";
-      print "STATIC const char *const parsekwd[] = {"}
+      print "static const char *const parsekwd[] = {"}
 /TNOT/,/neverfound/{if (last) print "	\"" last
"\","; last = $3}
 END{print "	\"" last "\"\n};"}'
 
diff --git a/usr/dash/parser.c b/usr/dash/parser.c
index 6e076a59..572cbcd5 100644
--- a/usr/dash/parser.c
+++ b/usr/dash/parser.c
@@ -64,7 +64,7 @@
  */
 
 /* values returned by readtoken */
-#include "token.h"
+#include "token_vars.h"
 
 
 
@@ -86,7 +86,7 @@ struct heredoc *heredoclist;	/* list of here documents to read
*/
 int doprompt;			/* if set, prompt the user */
 int needprompt;			/* true if interactive and at start of line */
 int lasttoken;			/* last token read */
-MKINIT int tokpushback;		/* last token pushed back */
+int tokpushback;		/* last token pushed back */
 char *wordtext;			/* text of last word returned by readtoken */
 int checkkwd;
 struct nodelist *backquotelist;
@@ -210,6 +210,7 @@ list(int nlflag)
 				parseheredoc();
 			else
 				pungetc();		/* push back EOF on input */
+			tokpushback++;
 			return n1;
 		default:
 			if (nlflag == 1)
diff --git a/usr/dash/parser.h b/usr/dash/parser.h
index e6caed63..2875cce6 100644
--- a/usr/dash/parser.h
+++ b/usr/dash/parser.h
@@ -34,6 +34,8 @@
  *	@(#)parser.h	8.3 (Berkeley) 5/4/95
  */
 
+#include "token.h"
+
 /* control characters in argument strings */
 #define CTL_FIRST -127		/* first 'special' character */
 #define CTLESC -127		/* escape next character */
@@ -73,6 +75,7 @@
  * must be distinct from NULL, so we use the address of a variable that
  * happens to be handy.
  */
+extern int lasttoken;
 extern int tokpushback;
 #define NEOF ((union node *)&tokpushback)
 extern int whichprompt;		/* 1 == PS1, 2 == PS2 */
@@ -91,3 +94,8 @@ goodname(const char *p)
 {
 	return !*endofname(p);
 }
+
+static inline int parser_eof(void)
+{
+	return tokpushback && lasttoken == TEOF;
+}