[perl #78674] Fix stack pointer corruption in pp_concat() with 'use encoding'

sv_utf8_upgrade_nomg() may reallocate the stack via sv_recode_to_utf8()
if 'use encoding' is in effect, causing stack pointer corruption.

1 files changed, 3 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index fd270e9798..f4d79dc5da 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -275,6 +275,8 @@ PP(pp_concat)
 	rbyte = !DO_UTF8(right);
     }
     if (lbyte != rbyte) {
+	/* sv_utf8_upgrade_nomg() may reallocate the stack */
+	PUTBACK;
 	if (lbyte)
 	    sv_utf8_upgrade_nomg(TARG);
 	else {
@@ -283,6 +285,7 @@ PP(pp_concat)
 	    sv_utf8_upgrade_nomg(right);
 	    rpv = SvPV_nomg_const(right, rlen);
 	}
+	SPAGAIN;
     }
     sv_catpvn_nomg(TARG, rpv, rlen);