unix: stop using pthread_yield()

This symbol was removed from glibc 2.34. Its replacement (sched_yield())
appears to have been available forever. So we disable the usage of
pthread_yield(). We also add verification for ELF banned symbols.

cpython-unix/build-bdb.sh

@@ -13,12 +13,19 @@ tar -xf db-${BDB_VERSION}.tar.gz
 
 pushd db-${BDB_VERSION}/build_unix
 
+CONFIGURE_FLAGS="--enable-dbm --disable-shared"
+
+# configure looks for pthread_yield(), which was dropped from glibc 2.34.
+# Its replacement is sched_yield(). Fortunately, bdb's source code will fall
+# back to sched_yield() if pthread_yield() isn't available. So we just lie
+# to configure and tell it pthread_yield() isn't available.
+CONFIGURE_FLAGS="${CONFIGURE_FLAGS} ac_cv_func_pthread_yield=no"
+
 CFLAGS="${EXTRA_TARGET_CFLAGS} -fPIC" CPPFLAGS="${EXTRA_TARGET_CFLAGS} -fPIC" ../dist/configure \
     --build=${BUILD_TRIPLE} \
     --host=${TARGET_TRIPLE} \
     --prefix=/tools/deps \
-    --enable-dbm \
-    --disable-shared
+    ${CONFIGURE_FLAGS}
 
 make -j ${NUM_CPUS}
 make -j ${NUM_CPUS} install DESTDIR=${ROOT}/out

src/validation.rs

@@ -362,6 +362,11 @@ static PLATFORM_TAG_BY_TRIPLE: Lazy<HashMap<&'static str, &'static str>> = Lazy:
     .collect()
 });
 
+const ELF_BANNED_SYMBOLS: &[&str] = &[
+    // Deprecated as of glibc 2.34 in favor of sched_yield.
+    "pthread_yield",
+];
+
 /// Symbols that we don't want to appear in mach-o binaries.
 const MACHO_BANNED_SYMBOLS_NON_AARCH64: &[&str] = &[
     // _readv and _pwritev are introduced when building with the macOS 11 SDK.
@@ -524,6 +529,14 @@ fn validate_elf(
         undefined_symbols.sort();
 
         for symbol in undefined_symbols {
+            if ELF_BANNED_SYMBOLS.contains(&symbol.symbol.as_str()) {
+                errors.push(format!(
+                    "{} defines banned ELF symbol {}",
+                    path.display(),
+                    symbol.symbol,
+                ));
+            }
+
             if let Some(version) = &symbol.version {
                 let parts: Vec<&str> = version.splitn(2, '_').collect();