Update: I think GCC silently decides your architecture supports atomic builtins if you use them, and this causes problems if you inline uses of them across modules. I think something here is a bug, I'm just not sure what. Download the attachment and run: g++ atomic_int_gcc.cpp This file uses __sync_add_and_fetch directly and builds fine. Then try this: g++ the_inline_test.cpp inline_test_user.cpp In this case the_inline_test.cpp uses a function defined by inline_test_user.cpp that uses an inline function that uses __sync_add_and_fetch. It will result in a linker error. You have to compile like this (assuming x86): g++ -march=i686 the_inline_test.cpp inline_test_user.cpp If the lock instruction has been around since the 386, why do I need to specify i686? If I really do need to specify i686, why don't I need to specify it for atomic_int_gcc.cpp? If this is by design, it seems to violate the principle of least surprise. On Mon, Jun 8, 2009 at 2:32 PM, Joseph Garvin<joseph.h.garvin@xxxxxxxxx> wrote: > I wasn't going to ask this because I thought it was peculiar to my > custom build environment, but I discovered this is no longer true. > > If I manually call gcc to compile a file that uses the atomic built-in > __sync_add_and_fetch, it compiles and links fine. But if I use it in > an autotool'd project, linking will fail complaining that > __sync_add_and_fetch doesn't exist. No custom march or cflags are > being set. How is this possible? O_o Is there anyway that GCC will > choose to compile with atomic builtins disabled without specifying a > march flag? > > I've tried the manual compile with/without -D_REENTRANT, -g, and -O2 > and it makes no difference. Always succeeds. The only other thing I > can think of is that somehow what is *linked* against can cause GCC to > drop atomic builtins. Is this known to happen? The implication is my > configure test for the presence of __sync_add_and_fetch always > succeeds even though my app won't build, defeating its point. >
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