x86/asm/64: Open-code register save/restore in trace_hardirqs*() thunks

This is a preparatory patch for change in "struct pt_regs"
handling in entry_64.S.

trace_hardirqs*() thunks were (ab)using a part of the
'pt_regs' handling code, namely the SAVE_ARGS/RESTORE_ARGS
macros, to save/restore registers across C function calls.

Since SAVE_ARGS is going to be changed, open-code
register saving/restoring here.

Incidentally, this removes a bit of dead code:
one SAVE_ARGS was used just to emit a CFI annotation,
but it also generated unreachable assembly instructions.

Take a page from thunk_32.S and use push/pop instructions
instead of movq, they are far shorter:
1 or 2 bytes versus 5, and no need for instructions to adjust %rsp:

   text	   data	    bss	    dec	    hex	filename
    333	     40	      0	    373	    175	thunk_64_movq.o
    104	     40	      0	    144	     90	thunk_64_push_pop.o

[ This is ugly as sin, but we'll fix up the ugliness in the next
  patch. I see no point in reordering patches just to avoid an
  ugly intermediate state.  --Andy ]

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1420927210-19738-4-git-send-email-dvlasenk@redhat.com
Link: http://lkml.kernel.org/r/4c979ad604f0f02c5ade3b3da308b53eabd5e198.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/lib/thunk_64.S

@@ -17,9 +17,27 @@
 	CFI_STARTPROC
 
 	/* this one pushes 9 elems, the next one would be %rIP */
-	SAVE_ARGS
+	pushq_cfi %rdi
+	CFI_REL_OFFSET rdi, 0
+	pushq_cfi %rsi
+	CFI_REL_OFFSET rsi, 0
+	pushq_cfi %rdx
+	CFI_REL_OFFSET rdx, 0
+	pushq_cfi %rcx
+	CFI_REL_OFFSET rcx, 0
+	pushq_cfi %rax
+	CFI_REL_OFFSET rax, 0
+	pushq_cfi %r8
+	CFI_REL_OFFSET r8, 0
+	pushq_cfi %r9
+	CFI_REL_OFFSET r9, 0
+	pushq_cfi %r10
+	CFI_REL_OFFSET r10, 0
+	pushq_cfi %r11
+	CFI_REL_OFFSET r11, 0
 
 	.if \put_ret_addr_in_rdi
+	/* 9*8(%rsp) is return addr on stack */
 	movq_cfi_restore 9*8, rdi
 	.endif
 
@@ -45,11 +63,31 @@
 #endif
 #endif
 
-	/* SAVE_ARGS below is used only for the .cfi directives it contains. */
+#if defined(CONFIG_TRACE_IRQFLAGS) \
+ || defined(CONFIG_DEBUG_LOCK_ALLOC) \
+ || defined(CONFIG_PREEMPT)
 	CFI_STARTPROC
-	SAVE_ARGS
+	CFI_ADJUST_CFA_OFFSET 9*8
 restore:
-	RESTORE_ARGS
+	popq_cfi %r11
+	CFI_RESTORE r11
+	popq_cfi %r10
+	CFI_RESTORE r10
+	popq_cfi %r9
+	CFI_RESTORE r9
+	popq_cfi %r8
+	CFI_RESTORE r8
+	popq_cfi %rax
+	CFI_RESTORE rax
+	popq_cfi %rcx
+	CFI_RESTORE rcx
+	popq_cfi %rdx
+	CFI_RESTORE rdx
+	popq_cfi %rsi
+	CFI_RESTORE rsi
+	popq_cfi %rdi
+	CFI_RESTORE rdi
 	ret
 	CFI_ENDPROC
 	_ASM_NOKPROBE(restore)
+#endif