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Message-ID: <20261111041815.4001816-1-khem.raj@oss.qualcomm.com>
Date: Tue, 10 Nov 2026 20:18:15 -0800
From: Khem Raj <raj.khem@...il.com>
To: musl@...ts.openwall.com
Cc: Khem Raj <khem.raj@....qualcomm.com>
Subject: [PATCH v2] math: enable FENV_ACCESS in expm1, expm1f, hypot and hypotf
These functions rely on floating point exception flags being raised
exactly as the C code would raise them, but without FENV_ACCESS the
compiler may assume the flags are never inspected. Clang does, and
speculates floating point operations across branches. Built with
clang 23 for aarch64 (-mcpu=cortex-a57), expm1() computes both
y*2.0*0x1p1023 and y*twopk for the k < 0 || k > 56 case and picks
one with fcsel, so the unused multiply raises a spurious OVERFLOW.
libc-test's math/expm1, expm1f, hypot, hypotf and sinh (via expm1)
fail because of that.
GCC does not speculate these operations, so GCC builds are unchanged.
---
v2: Fix by adding pragma STDC FENV_ACCESS in source files
src/math/expm1.c | 1 +
src/math/expm1f.c | 1 +
src/math/hypot.c | 1 +
src/math/hypotf.c | 1 +
4 files changed, 4 insertions(+)
diff --git a/src/math/expm1.c b/src/math/expm1.c
index ac1e61e..81d0c80 100644
--- a/src/math/expm1.c
+++ b/src/math/expm1.c
@@ -105,6 +105,7 @@
*/
#include "libm.h"
+#pragma STDC FENV_ACCESS ON
static const double
o_threshold = 7.09782712893383973096e+02, /* 0x40862E42, 0xFEFA39EF */
diff --git a/src/math/expm1f.c b/src/math/expm1f.c
index 09a41af..8c7aa18 100644
--- a/src/math/expm1f.c
+++ b/src/math/expm1f.c
@@ -14,6 +14,7 @@
*/
#include "libm.h"
+#pragma STDC FENV_ACCESS ON
static const float
ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
diff --git a/src/math/hypot.c b/src/math/hypot.c
index 6071bf1..0efc546 100644
--- a/src/math/hypot.c
+++ b/src/math/hypot.c
@@ -1,6 +1,7 @@
#include <math.h>
#include <stdint.h>
#include <float.h>
+#pragma STDC FENV_ACCESS ON
#if FLT_EVAL_METHOD > 1U && LDBL_MANT_DIG == 64
#define SPLIT (0x1p32 + 1)
diff --git a/src/math/hypotf.c b/src/math/hypotf.c
index 2fc214b..91fc086 100644
--- a/src/math/hypotf.c
+++ b/src/math/hypotf.c
@@ -1,5 +1,6 @@
#include <math.h>
#include <stdint.h>
+#pragma STDC FENV_ACCESS ON
float hypotf(float x, float y)
{
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