Le Mon, 07 Apr 2014 16:36:18 +0200, Corinna Vinschen a écrit : > On Apr 7 14:02, Jean-Pierre Flori wrote: >> Le Mon, 07 Apr 2014 13:28:19 +0000, Jean-Pierre Flori a écrit : >> >> > Le Mon, 07 Apr 2014 13:57:30 +0200, Corinna Vinschen a écrit : >> > >> >> On Apr 7 11:50, Jean-Pierre Flori wrote: >> >>> Le Mon, 07 Apr 2014 13:30:27 +0200, Corinna Vinschen a écrit : >> >>> > >> >>> > I'm sorry, but I don't know how this works exactly. The nm >> >>> > prefix is only added for external references, not for inlined >> >>> > functions, but I don't know the gory details. You may be better >> >>> > off to ask on the gcc mailing list. >> >>> > >> >>> No problem, I've already learned tons of stuff thanks to your help. >> >>> I've just posted on gcc-help. >> >>> http://gcc.gnu.org/ml/gcc-help/2014-04/msg00024.html >> >> >> >> Thanks. A simple testcase would still be nice, of course. >> >> >> >> >> > Sure, but it seems the issue is that I cannot get the __nm_ prefix >> > when I elaborate on a minimal problem like you did. >> > >> > I'll still try to get something this afternoon. >> I think I got something: >> $ cat > lib.c <<EOF #include <stdio.h> >> >> int foo (int a) >> { >> printf ("a = %d\n", a); >> return a; >> } >> EOF $cat > asm.as <<EOF global nothing ;export nothing nothing: >> ret end >> EOF $ cat > app.c <<EOF #include <stdio.h> >> >> extern int foo (int); >> >> int main () >> { >> int x = foo (42); printf ("x = %d\n", x); >> nothing(); >> return 0; >> } >> EOF $ gcc -g -c lib.c -o lib.o $ yasm -fx64 asm.as -o asm.o $ gcc >> -shared lib.o ams.o -Wl,--out-implib=lib.dll.a -Wl,--export-all- >> symbols -o lib.dll $ gcc -g -o app app.c -L. -llib $ ./app ... >> <segfault> >> >> Without the export directive (commented above) I get __nm_ prefix and >> wrong callq instruction. >> With it, the __nm_prefix disappears and the trampoline correctly used. > > I think you must define the export (gas: .def) pseudo op when creating > your own assembler code exporting a symbol from a DLL. If you look into > the code created by gcc from lib.c: > > $ gcc -S lib.c $ cat lib.s > .file "lib.c" > .section .rdata,"dr" > .LC0: > .ascii "a = %d\12\0" > .text .globl foo .def foo; .scl 2; .type 32; > .endef .seh_proc foo > foo: > pushq %rbp .seh_pushreg %rbp movq %rsp, %rbp > .seh_setframe %rbp, 0 subq $32, %rsp .seh_stackalloc 32 > .seh_endprologue movl %ecx, 16(%rbp) > movl 16(%rbp), %edx leaq .LC0(%rip), %rcx call printf > movl 16(%rbp), %eax addq $32, %rsp popq %rbp ret > .seh_endproc .ident "GCC: (GNU) 4.8.2" > .def printf; .scl 2; .type 32; .endef > > At this point gcc doesn't know that foo will get exported from a DLL, > but it generates the .def directive nevertheless. If I create the same > code in gas: > > .text .globl nothing .def nothing; .scl 2; .type 32; .endef > nothing: > ret > > then it works, but crashes if I omit the .def directive. So it seems to > me you don't have to export the symbol using the dllimport/dllexport > directives, but you have to specify the symbol explicitely for export. > Exactly! I came to the same conclusion. On top of that, it seems that including the export stuff does not hurt when building and linking a static lib.
What's strange is that when we use the dllimport magic then it works even though the symbol was not explicitely exported. Thanks for the support. JP -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple