D3698: chg: fix an undefined behavior about memcpy

[quark (Jun Wu)]

quark created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  Spot by Wez Furlong.  `memcpy(x, NULL, 0)` is undefined according to [1]:
  
  [1]: https://stackoverflow.com/questions/5243012

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3698

AFFECTED FILES
  contrib/chg/chg.c

CHANGE DETAILS

diff --git a/contrib/chg/chg.c b/contrib/chg/chg.c
--- a/contrib/chg/chg.c
+++ b/contrib/chg/chg.c
@@ -220,7 +220,10 @@
 
 	const char **argv = mallocx(sizeof(char *) * argsize);
 	memcpy(argv, baseargv, sizeof(baseargv));
-	memcpy(argv + baseargvsize, opts->args, sizeof(char *) * opts->argsize);
+	if (opts->args) {
+		size_t size = sizeof(char *) * opts->argsize;
+		memcpy(argv + baseargvsize, opts->args, size);
+	}
 	argv[argsize - 1] = NULL;
 
 	if (putenv("CHGINTERNALMARK=") != 0)



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