From 8ea883a60390fa307786a705ff8af4fb1a4be6e6 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Tue, 20 Aug 2019 23:29:19 -0700
Subject: [PATCH] Workaround a rounding difference in the strtof function in
 Centos 6. (#290)

* Workaround a rounding difference in the strtof function in Centos 6.

This difference causes the spec test const.wast to fail, so disable the
test on platforms where we detect the rounding difference occurs.
---
 Cargo.toml |  4 ++++
 build.rs   | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index bc6b1c3256..fa7c07ed75 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -38,6 +38,10 @@ errno = "0.2.4"
 rayon = "1.1"
 wasm-webidl-bindings = "0.4"
 
+# build.rs tests whether to enable a workaround for the libc strtof function.
+[target.'cfg(target_os = "linux")'.build-dependencies]
+libc = "0.2.60"
+
 [workspace]
 members = [
   "misc/wasmtime-rust",
diff --git a/build.rs b/build.rs
index e1591d4131..8acbdfb85c 100644
--- a/build.rs
+++ b/build.rs
@@ -154,5 +154,30 @@ fn ignore(testsuite: &str, name: &str) -> bool {
             (_, _) => false,
         };
     }
+
+    #[cfg(target_os = "linux")]
+    {
+        // Test whether the libc correctly parses the following constant; if so,
+        // we can run the "const" test. If not, the "const" test will fail, since
+        // we use wabt to parse the tests and wabt uses strtof.
+        extern "C" {
+            pub fn strtof(s: *const libc::c_char, endp: *mut *mut libc::c_char) -> libc::c_float;
+        }
+        if unsafe {
+            strtof(
+                b"8.8817847263968443574e-16" as *const u8 as *const libc::c_char,
+                std::ptr::null_mut(),
+            )
+        }
+        .to_bits()
+            != 0x26800001
+        {
+            return match (testsuite, name) {
+                ("spec_testsuite", "const") => true,
+                (_, _) => false,
+            };
+        }
+    }
+
     false
 }