bfd: add AMDGCN architecture

Add support for the AMDGCN architecture to BFD.

This is the bare minimum to get

  $ ./configure --target=amdgcn-hsa-amdhsa --disable-gas
  $ make all-binutils

working later in this series.

The specific AMDGCN models added here are a bit arbitrary, based on
what we intend to initially support in GDB.  This list will need to be
updated in the future anyway.  The complete up-to-date list of existing
AMDGPU models can be found here:

  https://llvm.org/docs/AMDGPUUsage.html#processors

The ELF format for this architecture is documented here:

  https://llvm.org/docs/AMDGPUUsage.html#elf-code-object

The flags for the "HSA" OS ABI are properly versioned and documented on
that page.  But the NONE, PAL and MESA3D OS ABIs are not well documented
nor versioned.  Taking a peek at the LLVM source code, we see that they
encode their flags the same way as HSA v3.  For example, for PAL:

  c8b614cd74/llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUTargetStreamer.cpp (L601)

So at least, we know that all AMDGPU objects (of which AMDGCN objects
are a subset of) at the time of writing encode the specific GPU model in
the EF_AMDGPU_MACH field of e_flags.

bfd/ChangeLog:

	* Makefile.am (ALL_MACHINES, ALL_MACHINES_CFILES):
	Add cpu-amdgcn.c.
	(BFD64_BACKENDS): Add elf64-amdgcn.lo.
	(BFD64_BACKENDS_CFILES): Add elf64-amdgcn.c.
	* Makefile.in: Re-generate.
	* cpu-amdgcn.c: New.
	* elf64-amdgcn.c: New.
	* archures.c (bfd_architecture): Add bfd_arch_amdgcn and related
	mach defines.
	(bfd_amdgcn_arch): New.
	(bfd_archures_list): Add bfd_amdgcn_arch.
	* bfd-in2.h: Re-generate.
	* config.bfd: Handle amdgcn* target.
	* configure.ac: Handle amdgcn_elf64_le_vec.
	* configure: Re-generate.
	* elf-bfd.h (elf_target_id): Add AMDGCN_ELF_DATA.
	* targets.c (amdgcn_elf64_le_vec): New.
	(_bfd_target_vector): Add amdgcn_elf64_le_vec.

include/ChangeLog:

	* elf/amdgpu.h: New.
	* elf/common.h (ELFOSABI_AMDGPU_HSA): Add.

Change-Id: I969f7b14960797e88891c308749a6e341eece5b2

include/elf/amdgpu.h

@@ -0,0 +1,36 @@
+/* AMDGPU ELF support for BFD.
+
+   Copyright (C) 2019-2021 Free Software Foundation, Inc.
+
+   This file is part of BFD, the Binary File Descriptor library.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef _ELF_AMDGPU_H
+#define _ELF_AMDGPU_H
+
+/* e_ident[EI_ABIVERSION] values, when e_ident[EI_OSABI] is
+   ELFOSABI_AMDGPU_HSA.  */
+
+#define ELFABIVERSION_AMDGPU_HSA_V2 0
+#define ELFABIVERSION_AMDGPU_HSA_V3 1
+#define ELFABIVERSION_AMDGPU_HSA_V4 2
+#define ELFABIVERSION_AMDGPU_HSA_V5 3
+
+/* Processor selection mask for EF_AMDGPU_MACH_* values.  */
+
+#define EF_AMDGPU_MACH 0x0ff
+#define EF_AMDGPU_MACH_AMDGCN_MIN 0x020
+
+#endif /* _ELF_AMDGPU_H */

include/elf/common.h

@@ -77,6 +77,7 @@
 #define ELFOSABI_OPENVOS     18 /* Stratus Technologies OpenVOS */
 
 #define ELFOSABI_C6000_ELFABI 64 /* Bare-metal TMS320C6000 */
+#define ELFOSABI_AMDGPU_HSA  64 /* AMD HSA Runtime */
 #define ELFOSABI_C6000_LINUX 65 /* Linux TMS320C6000 */
 #define ELFOSABI_ARM_FDPIC   65 /* ARM FDPIC */
 #define ELFOSABI_ARM	     97	/* ARM */