Redo the glibc compatibility issues workaround, see comment for details

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index cec1f29cdf229665624043356927ef6fd1fccd8b..cf16a6528ea3c6238875c26851c645200d2c1301 100644 (file)
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,7 +15,7 @@ jobs:
         run: |
           apt-get update
           apt-get -y dist-upgrade
-          apt-get -y install cargo libstd-rust-dev-wasm32 valgrind lld git g++ clang openjdk-11-jdk maven faketime zip unzip
+          apt-get -y install cargo libstd-rust-dev-wasm32 valgrind lld git g++ clang openjdk-11-jdk maven faketime zip unzip llvm
       - name: Checkout source code
         uses: actions/checkout@v2
         with:

diff --git a/genbindings.sh b/genbindings.sh
index 7ecbdeba7e59ed278dafbb2d9e50d16f838099c4..9529fc0815fba15c2b511dbba8bd657ba67ef9fa 100755 (executable)
--- a/genbindings.sh
+++ b/genbindings.sh
@@ -84,18 +84,49 @@ if [ "$3" = "true" ]; then
        [ "$IS_MAC" = "false" ] && COMPILE="$COMPILE -Wl,-wrap,calloc -Wl,-wrap,realloc -Wl,-wrap,reallocarray -Wl,-wrap,malloc -Wl,-wrap,free"
        $COMPILE -o liblightningjni_debug$LDK_TARGET_SUFFIX.so -g -fsanitize=address -shared-libasan -rdynamic -I"$1"/lightning-c-bindings/include/ $2 src/main/jni/bindings.c "$1"/lightning-c-bindings/target/$LDK_TARGET/debug/libldk.a -lm
 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 can simply define it explicitly here, forcing rust to use the fallback." >> 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.
+               # 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).
+               # This issue persists not only with directly providing a symbol, but also ld.lld's -wrap
+               # and --defsym arguments.
+               # In smaller programs, it appears to be possible to work around this with -Bsymbolic and
+               # -nostdlib, however when applied the full-sized JNI library here it no longer works.
+               # 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.
+               [ ! -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$" || echo)" != "" ]; then
+                       echo "Archive contained non-object files!"
+                       exit 1
+               fi
+               if [ "$(ar t "$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a | grep ldk.ldk.*-cgu.*.rcgu.o | wc -l)" != "1" ]; then
+                       echo "Archive contained more than one LDK object file"
+                       exit 1
+               fi
+               mkdir -p tmp
+               rm -f tmp/*
+               ar x --output=tmp "$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a
+               pushd tmp
+               llvm-dis ldk.ldk.*-cgu.*.rcgu.o
+               sed -i 's/br i1 icmp eq (i8\* @__cxa_thread_atexit_impl, i8\* null)/br i1 icmp eq (i8* null, i8* null)/g' ldk.ldk.*-cgu.*.rcgu.o.ll
+               llvm-as ldk.ldk.*-cgu.*.rcgu.o.ll -o ./libldk.bc
+               ar q libldk.a *.o
+               popd
+               LDK_LIB="tmp/libldk.bc tmp/libldk.a"
        fi
-       $COMPILE -o liblightningjni_release$LDK_TARGET_SUFFIX.so -flto -O3 -I"$1"/lightning-c-bindings/include/ $2 src/main/jni/bindings.c "$1"/lightning-c-bindings/target/$LDK_TARGET/release/libldk.a
+       $COMPILE -o liblightningjni_release$LDK_TARGET_SUFFIX.so -flto -O3 -I"$1"/lightning-c-bindings/include/ $2 src/main/jni/bindings.c $LDK_LIB
        if [ "$IS_MAC" = "false" ]; then
-               set +e # grep exits with 1 if no lines were left, which is our success condition
-               GLIBC_SYMBS="$(objdump -T liblightningjni_release$LDK_TARGET_SUFFIX.so | grep GLIBC_ | grep -v "GLIBC_2\.2\." | grep -v "GLIBC_2\.3\(\.\| \)" | grep -v "GLIBC_2.\(14\|17\) ")"
-               set -e
+               GLIBC_SYMBS="$(objdump -T liblightningjni_release$LDK_TARGET_SUFFIX.so | grep GLIBC_ | grep -v "GLIBC_2\.2\." | grep -v "GLIBC_2\.3\(\.\| \)" | grep -v "GLIBC_2.\(14\|17\) " || echo)"
                if [ "$GLIBC_SYMBS" != "" ]; then
                        echo "Unexpected glibc version dependency! Some users need glibc 2.17 support, symbols for newer glibcs cannot be included."
                        echo "$GLIBC_SYMBS"