--- Begin Message ---
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Subject: |
'volatile' needed for local variables around vfork |
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Date: |
Sat, 19 Mar 2011 21:39:30 -0700 |
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User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.14) Gecko/20110223 Thunderbird/3.1.8 |
In three places, GNU Emacs assumes that a local variable
is preserved after a successful vfork, but on some architectures
these variables may be clobbered. (I found this problem by
compiling with gcc -Wclobbered.) I plan to address this problem
with the following patch:
2011-03-19 Paul Eggert <address@hidden>
* callproc.c (Fcall_process): Use 'volatile' to avoid vfork clobbering.
* process.c (create_process): Likewise.
* sysdep.c (sys_subshell): Likewise.
Previously, the sys_subshell 'volatile' was incorrectly IF_LINTted out.
=== modified file 'src/callproc.c'
--- src/callproc.c 2011-03-18 04:45:18 +0000
+++ src/callproc.c 2011-03-18 05:56:46 +0000
@@ -180,7 +180,7 @@
(int nargs, register Lisp_Object *args)
{
Lisp_Object infile, buffer, current_dir, path;
- int display_p;
+ volatile int display_p_volatile;
int fd[2];
int filefd;
register int pid;
@@ -190,6 +190,7 @@
int bufsize = CALLPROC_BUFFER_SIZE_MIN;
int count = SPECPDL_INDEX ();
+ const unsigned char **volatile new_argv_volatile;
register const unsigned char **new_argv;
/* File to use for stderr in the child.
t means use same as standard output. */
@@ -343,7 +344,7 @@
UNGCPRO;
}
- display_p = INTERACTIVE && nargs >= 4 && !NILP (args[3]);
+ display_p_volatile = INTERACTIVE && nargs >= 4 && !NILP (args[3]);
filefd = emacs_open (SSDATA (infile), O_RDONLY, 0);
if (filefd < 0)
@@ -371,7 +372,7 @@
&& SREF (path, 1) == ':')
path = Fsubstring (path, make_number (2), Qnil);
- new_argv = (const unsigned char **)
+ new_argv_volatile = new_argv = (const unsigned char **)
alloca (max (2, nargs - 2) * sizeof (char *));
if (nargs > 4)
{
@@ -542,6 +543,8 @@
pid = vfork ();
+ new_argv = new_argv_volatile;
+
if (pid == 0)
{
if (fd[0] >= 0)
@@ -673,6 +676,7 @@
int first = 1;
EMACS_INT total_read = 0;
int carryover = 0;
+ int display_p = display_p_volatile;
int display_on_the_fly = display_p;
struct coding_system saved_coding;
=== modified file 'src/process.c'
--- src/process.c 2011-03-20 02:48:50 +0000
+++ src/process.c 2011-03-20 03:07:54 +0000
@@ -1912,8 +1912,7 @@
/* child_setup must clobber environ on systems with true vfork.
Protect it from permanent change. */
char **save_environ = environ;
-
- current_dir = ENCODE_FILE (current_dir);
+ volatile Lisp_Object encoded_current_dir = ENCODE_FILE (current_dir);
#ifndef WINDOWSNT
pid = vfork ();
@@ -2054,13 +2053,13 @@
child_setup_tty (xforkout);
#ifdef WINDOWSNT
pid = child_setup (xforkin, xforkout, xforkout,
- new_argv, 1, current_dir);
+ new_argv, 1, encoded_current_dir);
#else /* not WINDOWSNT */
#ifdef FD_CLOEXEC
emacs_close (wait_child_setup[0]);
#endif
child_setup (xforkin, xforkout, xforkout,
- new_argv, 1, current_dir);
+ new_argv, 1, encoded_current_dir);
#endif /* not WINDOWSNT */
}
environ = save_environ;
=== modified file 'src/sysdep.c'
--- src/sysdep.c 2011-03-14 23:31:21 +0000
+++ src/sysdep.c 2011-03-18 05:50:40 +0000
@@ -488,7 +488,8 @@
int pid;
struct save_signal saved_handlers[5];
Lisp_Object dir;
- unsigned char * IF_LINT (volatile) str = 0;
+ unsigned char *volatile str_volatile = 0;
+ unsigned char *str;
int len;
saved_handlers[0].code = SIGINT;
@@ -512,7 +513,7 @@
goto xyzzy;
dir = expand_and_dir_to_file (Funhandled_file_name_directory (dir), Qnil);
- str = (unsigned char *) alloca (SCHARS (dir) + 2);
+ str_volatile = str = (unsigned char *) alloca (SCHARS (dir) + 2);
len = SCHARS (dir);
memcpy (str, SDATA (dir), len);
if (str[len - 1] != '/') str[len++] = '/';
@@ -544,6 +545,7 @@
sh = "sh";
/* Use our buffer's default directory for the subshell. */
+ str = str_volatile;
if (str && chdir ((char *) str) != 0)
{
#ifndef DOS_NT
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