x86,pm: Force out-of-line memcpy()

x86,pm: Force out-of-line memcpy()

GCC fancies inlining memcpy(), and because it cannot prove the
destination is page-aligned (it is) it ends up generating atrocious
code like:

 19e:   48 8b 15 00 00 00 00    mov    0x0(%rip),%rdx        # 1a5 <relocate_restore_code+0x25> 1a1: R_X86_64_PC32      core_restore_code-0x4
 1a5:   48 8d 78 08             lea    0x8(%rax),%rdi
 1a9:   48 89 c1                mov    %rax,%rcx
 1ac:   48 c7 c6 00 00 00 00    mov    $0x0,%rsi        1af: R_X86_64_32S       core_restore_code
 1b3:   48 83 e7 f8             and    $0xfffffffffffffff8,%rdi
 1b7:   48 29 f9                sub    %rdi,%rcx
 1ba:   48 89 10                mov    %rdx,(%rax)
 1bd:   48 8b 15 00 00 00 00    mov    0x0(%rip),%rdx        # 1c4 <relocate_restore_code+0x44> 1c0: R_X86_64_PC32      core_restore_code+0xff4
 1c4:   48 29 ce                sub    %rcx,%rsi
 1c7:   81 c1 00 10 00 00       add    $0x1000,%ecx
 1cd:   48 89 90 f8 0f 00 00    mov    %rdx,0xff8(%rax)
 1d4:   c1 e9 03                shr    $0x3,%ecx
 1d7:   f3 48 a5                rep movsq %ds:(%rsi),%es:(%rdi)

Notably the alignment code generates a text reference to
code_restore_code+0xff8, for which objtool raises the objection:

  vmlinux.o: warning: objtool: relocate_restore_code+0x3d: relocation to !ENDBR: next_arg+0x18

Applying some __assume_aligned(PAGE_SIZE) improve code-gen to:

 19e:   48 89 c7                mov    %rax,%rdi
 1a1:   48 c7 c6 00 00 00 00    mov    $0x0,%rsi        1a4: R_X86_64_32S       core_restore_code
 1a8:   b9 00 02 00 00          mov    $0x200,%ecx
 1ad:   f3 48 a5                rep movsq %ds:(%rsi),%es:(%rdi)

And resolve the problem, however, none of this is important code and
a much simpler solution still is to force a memcpy() call:

 1a1:   ba 00 10 00 00          mov    $0x1000,%edx
 1a6:   48 c7 c6 00 00 00 00    mov    $0x0,%rsi        1a9: R_X86_64_32S       core_restore_code
 1ad:   e8 00 00 00 00          call   1b2 <relocate_restore_code+0x32> 1ae: R_X86_64_PLT32     __memcpy-0x4

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>