Re: [PATCH v2] PowerPC: fix external calls from modules built by the compile command

[Ulrich Weigand <Ulrich.Weigand@de.ibm.com>]

Abhay Kandpal <abhay@linux.ibm.com> wrote:

>A module built for the compile command is loaded into inferior memory
>without a linker, so it has no PLT.  On ELFv2 the default code model
>still emits a direct bl for a call to another module, leaving r12
unset
>and the caller's TOC pointer unrestored, and the callee then derives a
>wrong r2 from a stale r12.
>
>gdb.compile/compile-setjmp.exp shows this: the injected code calls
>setjmp, whose global entry point computes r2 from a stale r12, and the
>first TOC-relative load segfaults.
>
>-mlongcall makes the call indirect, but on its own it reaches the
target
>through a PLT entry, giving R_PPC64_PLT16_HA/LO_DS relocations that
BFD's
>generic linker rejects.  Adding -mno-pltseq resolves the call against
the
>module's own TOC instead, via R_PPC64_TOC16_HA/LO_DS, which GDB
already
>handles.  GCC then emits the r2 save and restore around the call
itself.

This is OK.

Thanks,
Ulrich