Move some macros used in .asm files into header files.

[egrimley-arm]

The macros are defined in offsets.h and the values are checked at compile time by offsets.c.

[egrimley-arm]

One could use a helper program on the host to automatically generate the header files that define the offsets, but that would be much more complex to implement and an ongoing maintenance burden in the build system. Since these offsets are very rarely changed, and any change of them will typically involve simultaneous intricate changes to assembly and code that generates assembly I don't think it makes sense to generate the header files automatically. Better just to check the values with something like this approach.

One could use the preprocessor to make the source slightly simpler in a way, but it would then be much more complex in another way, and the error message when an offset is incorrect would be less readable, I think. Currently the error message looks like this:

.../dynamorio/core/arch/aarch64/offsets.c:9:9: error: size of array ‘x1’ is negative
    9 |     int x1[dcontext_t_OFFSET_dstack == offsetof(dcontext_t, dstack) ? 1 : -1];

I think that makes perfect sense to a programmer, and, if not, there's the comment preceding it in the source.

Another option would be to generate an error message at run time. You would then have total control over what the message looks like, but an error at build time seems better.

And using static_assert is certainly worth considering. I'm a bit confused about which versions of static_assert (or _Static_assert or whatever) are available with which versions of which compilers, and which header files need to be included to make them work, so perhaps for DynamoRIO it's better to use something totally portable like this array length trick.

[derekbruening]

I think we could use static_assert as for C++ we require C++11 (and already use it in our C++ code), for Visual Studio we require VS2019, and while our UNIX has gnu99 the GNU extensions provide _Static_assert. Could do sthg like #if defined(__cplusplus) && !defined(_Static_assert) #define _Static_assert static_assert #endif and then use _Static_assert everywhere: or define a new STATIC_ASSERT that takes in a message.

[derekbruening]

I would agument the name: either asm_offsets.{c,h} or struct_offsets.{c,h}.

[derekbruening]

The general approach seems good: take advantage of our use of the preprocessor in our asm files to share a header with a checking file.