[tip:x86/asm] x86/asm/entry/64: Use more readable constants

[tip-bot for Denys Vlasenko]

Commit-ID:  911d2bb5ccaab102abbab2bb58438c75bc342ca9
Gitweb:     http://git.kernel.org/tip/911d2bb5ccaab102abbab2bb58438c75bc342ca9
Author:     Denys Vlasenko <dvlasenk@xxxxxxxxxx>
AuthorDate: Thu, 26 Feb 2015 14:40:36 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 4 Mar 2015 22:50:52 +0100

x86/asm/entry/64: Use more readable constants

Constants such as SS+8 or SS+8-RIP are mysterious.
In most cases, SS+8 is just meant to be SIZEOF_PTREGS,
SS+8-RIP is RIP's offset in the iret frame.

This patch changes some of these constants to be less
mysterious.

No code changes (verified with objdump).

Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1d20491384773bd606e23a382fac23ddb49b5178.1424989793.git.luto@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/calling.h |  2 ++
 arch/x86/kernel/entry_64.S     | 28 ++++++++++++++++------------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 4a7ceb9..3374235 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -88,6 +88,8 @@ For 32-bit we have the following conventions - kernel is built with
 #define RSP		19*8
 #define SS		20*8
 
+#define SIZEOF_PTREGS	21*8
+
 	.macro ALLOC_PT_GPREGS_ON_STACK addskip=0
 	subq	$15*8+\addskip, %rsp
 	CFI_ADJUST_CFA_OFFSET 15*8+\addskip
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 4669477..858e94e 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -164,12 +164,12 @@ ENDPROC(native_usergs_sysret64)
  * initial frame state for interrupts (and exceptions without error code)
  */
 	.macro INTR_FRAME start=1 offset=0
-	EMPTY_FRAME \start, SS+8+\offset-RIP
-	/*CFI_REL_OFFSET ss, SS+\offset-RIP*/
-	CFI_REL_OFFSET rsp, RSP+\offset-RIP
-	/*CFI_REL_OFFSET rflags, EFLAGS+\offset-RIP*/
-	/*CFI_REL_OFFSET cs, CS+\offset-RIP*/
-	CFI_REL_OFFSET rip, RIP+\offset-RIP
+	EMPTY_FRAME \start, 5*8+\offset
+	/*CFI_REL_OFFSET ss, 4*8+\offset*/
+	CFI_REL_OFFSET rsp, 3*8+\offset
+	/*CFI_REL_OFFSET rflags, 2*8+\offset*/
+	/*CFI_REL_OFFSET cs, 1*8+\offset*/
+	CFI_REL_OFFSET rip, 0*8+\offset
 	.endm
 
 /*
@@ -177,7 +177,7 @@ ENDPROC(native_usergs_sysret64)
  * with vector already pushed)
  */
 	.macro XCPT_FRAME start=1 offset=0
-	INTR_FRAME \start, RIP+\offset-ORIG_RAX
+	INTR_FRAME \start, 1*8+\offset
 	.endm
 
 /*
@@ -645,10 +645,14 @@ END(interrupt)
 	cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
 	CFI_DEF_CFA_REGISTER	rsi
 	pushq %rsi
+	/*
+	 * For debugger:
+	 * "CFA (Current Frame Address) is the value on stack + offset"
+	 */
 	CFI_ESCAPE	0x0f /* DW_CFA_def_cfa_expression */, 6, \
-			0x77 /* DW_OP_breg7 */, 0, \
+			0x77 /* DW_OP_breg7 (rsp) */, 0, \
 			0x06 /* DW_OP_deref */, \
-			0x08 /* DW_OP_const1u */, SS+8-RBP, \
+			0x08 /* DW_OP_const1u */, SIZEOF_PTREGS-RBP, \
 			0x22 /* DW_OP_plus */
 	/* We entered an interrupt context - irqs are off: */
 	TRACE_IRQS_OFF
@@ -674,7 +678,7 @@ ret_from_intr:
 
 	/* Restore saved previous stack */
 	popq %rsi
-	CFI_DEF_CFA rsi,SS+8-RBP	/* reg/off reset after def_cfa_expr */
+	CFI_DEF_CFA rsi,SIZEOF_PTREGS-RBP /* reg/off reset after def_cfa_expr */
 	/* return code expects complete pt_regs - adjust rsp accordingly: */
 	leaq -RBP(%rsi),%rsp
 	CFI_DEF_CFA_REGISTER	rsp
@@ -1549,7 +1553,7 @@ first_nmi:
 	.rept 5
 	pushq_cfi 11*8(%rsp)
 	.endr
-	CFI_DEF_CFA_OFFSET SS+8-RIP
+	CFI_DEF_CFA_OFFSET 5*8
 
 	/* Everything up to here is safe from nested NMIs */
 
@@ -1577,7 +1581,7 @@ repeat_nmi:
 	pushq_cfi -6*8(%rsp)
 	.endr
 	subq $(5*8), %rsp
-	CFI_DEF_CFA_OFFSET SS+8-RIP
+	CFI_DEF_CFA_OFFSET 5*8
 end_repeat_nmi:
 
 	/*
--
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