Fix xargs to obey POSIX's ARG_MAX restrictions.

This avoids "xargs: exec echo: Argument list too long" errors in practice.

find(1) needs to be fixed too, but that's a bit more complicated and a working
xargs provides a workaround.

Bug: http://b/65818597
Test: find /proc | strace -f -e execve ./toybox xargs echo > /dev/null

2 files changed, 14 insertions, 0 deletions

diff --git a/lib/lib.c b/lib/lib.c
index a4b7229b..70ad0758 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -1293,3 +1293,16 @@ void do_lines(int fd, void (*call)(char **pline, long len))
 
   if (fd) fclose(fp);
 }
+
+// Returns the number of bytes taken by the environment variables. For use
+// when calculating the maximum bytes of environment+argument data that can
+// be passed to exec for find(1) and xargs(1).
+long environ_bytes()
+{
+  long bytes = sizeof(char *);
+  char **ev;
+
+  for (ev = environ; *ev; ev++)
+    bytes += sizeof(char *) + strlen(*ev) + 1;
+  return bytes;
+}
diff --git a/lib/lib.h b/lib/lib.h
index a9a92fd9..889430bd 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -241,6 +241,7 @@ int regexec0(regex_t *preg, char *string, long len, int nmatch,
 char *getusername(uid_t uid);
 char *getgroupname(gid_t gid);
 void do_lines(int fd, void (*call)(char **pline, long len));
+long environ_bytes();
 
 #define HR_SPACE 1 // Space between number and units
 #define HR_B     2 // Use "B" for single byte units