Importing absolute symbols as constexpr

[Marcel Mueller]

AFAIK the address of an external symbol with static linkage can be used
as constexpr (e.g. a method reference as template parameter).

Is it also possible to import /absolute/ linker symbols this way?

Example

shader.o:
00000000 R shader
00000410 A shader_size

shader.h:
// import the shader symbol from shader.o, OK
extern unsigned shader[];

// Try to import shader_size - does not work
extern const int shader_size;
constexpr int shader_size_proxy = (int)&shader_size;
#define shader_size shader_size_proxy

// without constexpr
const int shader_size_proxy2 = (int)&shader_size;
#undef shader_size
#define shader_size shader_size_proxy2


The basic problem is that C++ only imports addresses but not absolute
values like the global symbol shader_size. And the following required
conversion from int* to int is no longer a valid constexpr.

Is there anything to come around this restriction?


Marcel

[Alf P. Steinbach]

Why can't you just provide the definition in a header file?


Cheers!,

- Alf

[Marcel Mueller]

On 13.04.17 18.24, Alf P. Steinbach wrote:
> Why can't you just provide the definition in a header file?

Of course, I can generate a matching header with hard coded constants.
But C++ compilation time on a Pi 1 is pure pain. So I favor just to link
the executable when the GPU code changes.


Marcel

[Ian Collins]

Use a cross-compiler?

--
Ian