在gdb中<值优化>是一个问题吗？

Question

I have an application that only crashes in -O2 optimization (compiled with gcc 4.2.4). When I step through the code and get to the spot that crashes and try to inspect the value, I get a "value optimized out" in gdb.

I read on the internet that this means that the value is stored in the register. I was wondering if my crash could be related to the fact that some information is placed in registers? Is there a way to print what is in the registers to see if it has been corrupted? Is there a way to keep optimizations but not use registers?

Thanks!

Answer 1

It's 99% likely to be a bug in your code and 1% likely to be a compiler code generation bug. So spend a proportionate amount of time looking for latent bugs in your code but be aware that you just may have found a code generation bug (in which case you'll need to study the compiler generated code carefully to see what the problem is).

Answer 2

try info registers in gdb.

You can disable optimization with -O0, but there's something fishy and I suggest you to investigate further and eventually post the code.

Answer 3

如果您可以检测程序流中的错误，您可以自己进行一些打印，如果它与内存泄漏和内存损坏有关，那么valgrind可能是比gdb更好的朋友。

Answer 4

This is not a problem, it is more of an issue with the aggressive optimizations in newer versions of gcc.

See: A Plan to Fix Local Variable Debug Information in GCC .

Answer 5

The one thing to watch is pointer aliasing, where the compiler can make assumptions that you do not comply with, for example that a pointer you pass into a function does not point to a global variable also used by that function. But you can control this with compiler options etc.