powerpc/vmlinux.lds: Define RUNTIME_DISCARD_EXIT

commit 4b9880dbf3bdba3a7c56445137c3d0e30aaa0a40 upstream.

The powerpc linker script explicitly includes .exit.text, because
otherwise the link fails due to references from __bug_table and
__ex_table. The code is freed (discarded) at runtime along with
.init.text and data.

That has worked in the past despite powerpc not defining
RUNTIME_DISCARD_EXIT because DISCARDS appears late in the powerpc linker
script (line 410), and the explicit inclusion of .exit.text
earlier (line 280) supersedes the discard.

However commit 99cb0d917ffa ("arch: fix broken BuildID for arm64 and
riscv") introduced an earlier use of DISCARD as part of the RO_DATA
macro (line 136). With binutils < 2.36 that causes the DISCARD
directives later in the script to be applied earlier [1], causing
.exit.text to actually be discarded at link time, leading to build
errors:

  '.exit.text' referenced in section '__bug_table' of crypto/algboss.o: defined in
  discarded section '.exit.text' of crypto/algboss.o
  '.exit.text' referenced in section '__ex_table' of drivers/nvdimm/core.o: defined in
  discarded section '.exit.text' of drivers/nvdimm/core.o

Fix it by defining RUNTIME_DISCARD_EXIT, which causes the generic
DISCARDS macro to not include .exit.text at all.

1: https://lore.kernel.org/lkml/87fscp2v7k.fsf@igel.home/

Fixes: 99cb0d917ffa ("arch: fix broken BuildID for arm64 and riscv")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230105132349.384666-1-mpe@ellerman.id.au
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/kernel/vmlinux.lds.S

@@ -6,6 +6,7 @@
 #endif
 
 #define BSS_FIRST_SECTIONS *(.bss.prominit)
+#define RUNTIME_DISCARD_EXIT
 
 #include <asm/page.h>
 #include <asm-generic/vmlinux.lds.h>