[PATCH 3/4] x86: open-code register save/restore in trace_hardirqs thunks

[Denys Vlasenko]

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 pt_regs
handling code, namely 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 insns.

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

Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Borislav Petkov <bp@xxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: X86 ML <x86@xxxxxxxxxx>
CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
CC: Will Drewry <wad@xxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/lib/thunk_64.S | 46 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S
index b30b5eb..8ec443a 100644
--- a/arch/x86/lib/thunk_64.S
+++ b/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
-- 
1.8.1.4

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