Don't explicitly override __cxa_thread_atexit_impl, rely on LLVM to optimize it out

diff --git a/genbindings.sh b/genbindings.sh
index 15a574da38f59f2f9ed4c7ebb04c070688637fc7..741f9de1f103fab385fdeba6a4d931c51333253a 100755 (executable)
--- a/genbindings.sh
+++ b/genbindings.sh
@@ -87,13 +87,13 @@ else
        LDK_LIB="$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a
        if [ "$IS_MAC" = "false" ]; then
                COMPILE="$COMPILE -Wl,--version-script=libcode.version -fuse-ld=lld"
-               echo "// __cxa_thread_atexit_impl is used to more effeciently cleanup per-thread local storage by rust libstd." >> src/main/jni/bindings.c
-               echo "// However, it is not available on glibc versions 2.17 or earlier, and rust libstd has a null-check and fallback in case it is missing." >> src/main/jni/bindings.c
-               echo "// Because it is weak-linked on the rust side, we should be able to simply define it explicitly here, forcing rust to use the fallback." >> src/main/jni/bindings.c
-               echo "void *__cxa_thread_atexit_impl = NULL;" >> src/main/jni/bindings.c
-               # Note that the above is not sufficient. For some reason involving ancient dark magic and
-               # haunted code segments, overriding the weak symbol only impacts sites which *call* the
-               # symbol in question, not sites which *compare with* the symbol in question.
+               # __cxa_thread_atexit_impl is used to more effeciently cleanup per-thread local storage by rust libstd.
+               # However, it is not available on glibc versions 2.17 or earlier, and rust libstd has a null-check and
+               # fallback in case it is missing.
+               # Because it is weak-linked on the rust side, we should be able to simply define it
+               # explicitly, forcing rust to use the fallback. However, for some reason involving ancient
+               # dark magic and haunted code segments, overriding the weak symbol only impacts sites which
+               # *call* the symbol in question, not sites which *compare with* the symbol in question.
                # This means that the NULL check in rust's libstd will always think the function is
                # callable while the function which is called ends up being NULL (leading to a jmp to the
                # zero page and a quick SEGFAULT).
@@ -104,6 +104,9 @@ else
                # After exhausting nearly every flag documented in lld, the only reliable method appears
                # to be editing the LDK binary. Luckily, LLVM's tooling makes this rather easy as we can
                # disassemble it into very readable code, edit it, and then reassemble it.
+               # Note that if we do so we don't have to bother overriding the actual call, LLVM should
+               # optimize it away, which also provides a good check that there isn't anything actually
+               # relying on it elsewhere.
                [ ! -f "$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a ] && exit 1
                if [ "$(ar t "$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a | grep -v "\.o$" || echo)" != "" ]; then
                        echo "Archive contained non-object files!"