https://bugs.llvm.org/show_bug.cgi?id=48681
Bug ID: 48681
Summary: lld --exclude-libs doesn't hide builtins when using
LTO
Product: lld
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Android uses --exclude-libs to hide symbols from the builtins and unwinder
libraries (e.g. libclang_rt.builtins-aarch64-android.a,
libgcc{,_real,_stripped}.a, libunwind_llvm.a, etc). When a symbol in one of
these excluded libraries isn't referenced by any LLVM IR input file, but is
referenced after the link-time compile step, then --exclude-libs fails to hide
the symbol.
Test script:
#!/bin/bash
set -e
LLVM=/x/llvm-upstream/stage1/bin
CC="$LLVM/clang -target x86_64-linux-gnu"
AR="$LLVM/llvm-ar"
cat >archive_func.c <<EOF
void __divti3() {}
EOF
cat >dso_func.c <<EOF
__int128 dso_func(__int128 x, __int128 y) { return x / y; }
EOF
$CC archive_func.c -fpic -c
rm -fr libarchive.a
$AR rcs libarchive.a archive_func.o
$CC -flto -c dso_func.c -fpic
$CC -flto -fuse-ld=lld -nostdlib dso_func.o -shared -o libdso.so
$PWD/libarchive.a -Wl,--exclude-libs,libarchive.a -Wl,-y,__divti3
$LLVM/llvm-readelf --dyn-syms -W libdso.so
Output:
$ ./test.sh
/x/mess/libarchive.a: lazy definition of __divti3
lto.tmp: reference to __divti3
/x/mess/libarchive.a(archive_func.o): definition of __divti3
Symbol table '.dynsym' contains 3 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000001370 6 FUNC GLOBAL DEFAULT 8 __divti3
2: 0000000000001380 99 FUNC GLOBAL DEFAULT 8 dso_func
I expected __divti3 to be hidden (and not appear in the `llvm-readelf
--dyn-syms` output). Removing the -flto argument when compiling dso_func.c (or
adding it when compiling archive_func.c) results in the expected output.
Both the Android platform and the NDK use --exclude-libs on builtins, but I'm
working on patches to instead mark the symbols in the archives hidden
(https://reviews.llvm.org/D93003 and https://reviews.llvm.org/D93431). I
noticed this bug while checking to see if I had unintentionally changed
anything in the platform build.
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