From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Fri, 18 Apr 2025 14:47:42 +0000 (-0300)
Subject: math: Fix UB in expm1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b59c34e8f93a7f2ebf2a3eb5ebb2ed6a0dc6e980;p=thirdparty%2Fglibc.git

math: Fix UB in expm1

Building with ubsan triggers:

UBSAN: Undefined behaviour in ../sysdeps/ieee754/dbl-64/s_expm1.c:242:4 left shift of 4294967271 by 20 cannot be represented in type 'int'

Since at the time k is always positive, just cast to uint32_t.
---

diff --git a/sysdeps/ieee754/dbl-64/s_expm1.c b/sysdeps/ieee754/dbl-64/s_expm1.c
index 1cafeca9c0..557178f33d 100644
--- a/sysdeps/ieee754/dbl-64/s_expm1.c
+++ b/sysdeps/ieee754/dbl-64/s_expm1.c
@@ -239,7 +239,7 @@ __expm1 (double x)
 	  uint32_t high;
 	  y = one - (e - x);
 	  GET_HIGH_WORD (high, y);
-	  SET_HIGH_WORD (y, high + (k << 20));  /* add k to y's exponent */
+	  SET_HIGH_WORD (y, high + ((uint32_t)k << 20));  /* add k to y's exponent */
 	  return y - one;
 	}
       t = one;