Re: [PATCHi v1] PowerPC: Create call stubs for compiled modules

Abhay Kandpal <[email protected]> wrote:

>The compile command loads a module into inferior memory and relocates
>it itself, without a linker.  For R_PPC64_REL24 it patches the branch
>to point directly at the target.  On ELFv2 that is not a valid call to
>another module: the callee derives its TOC pointer from r12, which
only
>a PLT-style call stub sets up, and the caller's TOC pointer is never
>restored because the nop following the bl is left alone.

On other platforms, the way this is supposed to work is to use a
set of compiler command-line options that result in code that does
not require PLTs for external calls.  Typically, this means to use
-mcmodel=large.

However, it seems that on PowerPC, while that option exists, it
generates code that still needs PLTs.  There is another option
-mlongcall that should avoid this, however.

I'm wondering if we were to just add -mlongcall to the platform-
specific compiler options for PowerPC, we could fix this issue
without having to reimplement a full PLT solution in GDB ...

Bye,
Ulrich