Hi there, I'm trying to replace _start with a custom implementation in my statically-linked binary on x86_64. I pass -nostartfiles to g++ and pass in crt1.o, crti.o, crtbegin.o and crtend.o, crtn.o (but with crt1.o replaced with my own implementation). This works, but I noticed that C++ exceptions stop working (they are never caught and cause a SIGABRT). After some debugging I discovered that the resulting executable does not have an .eh_frame section. So the issue is resolved by using -Wl,--eh-frame-hdr. But this doesn't seem to be required by the manual: https://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/Link-Options.html#index-shared_002dlibgcc-697 Also, using -static-libgcc and -shared-libgcc makes no difference. I suppose that with static linking, it always uses the static libgcc and this prevents exceptions from working correctly. It seems strange that as a user I need to specify -Wl,--eh-frame-hdr to resolve this. Couldn't this flag be inferred from the combination of -shared-libgcc and -static? (Since -shared-libgcc is supposed to enable exceptions in this context.) At least I feel that the documentation should be updated to mention this case. Suggestions welcome. See a complete test case below. Also, is there any easier way of just replacing _start? Note: this test case is also available right now at http://elfery.net/files/gcc-eh-test.sh ---- #!/bin/sh cat >throw.cpp <<EOF #include <iostream> int main() { try { throw "an exception"; } catch(const char *s) { std::cout << "caught " << s << " successfully\n"; } return 0; } EOF D=/usr/lib/x86_64-linux-gnu/ STARTFILES="$D/crt1.o $D/crti.o `gcc --print-file-name=crtbegin.o`" ENDFILES="`gcc --print-file-name=crtend.o` $D/crtn.o" echo dynamically linked should work... g++ throw.cpp -o throw -nostartfiles $STARTFILES $ENDFILES ./throw || true echo echo statically linked should fail... g++ -static throw.cpp -o throw -nostartfiles $STARTFILES $ENDFILES ./throw || true echo echo statically linked with -shared-libgcc doesn\'t help... g++ -static throw.cpp -o throw -nostartfiles $STARTFILES $ENDFILES -shared-libgcc ./throw || true echo echo statically linked with -static-libgcc doesn\'t help... g++ -static throw.cpp -o throw -nostartfiles $STARTFILES $ENDFILES -static-libgcc ./throw || true echo echo but statically linked with -Wl,--eh-frame-hdr works... g++ -static throw.cpp -o throw -nostartfiles $STARTFILES $ENDFILES -Wl,--eh-frame-hdr ./throw || true ---- $ ./test.sh dynamically linked should work... caught an exception successfully statically linked should fail... Aborted statically linked with -shared-libgcc doesn't help... Aborted statically linked with -static-libgcc doesn't help... Aborted but statically linked with -Wl,--eh-frame-hdr works... caught an exception successfully ---- Thanks, -- dwk
