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Subject[PATCH 11/11] x86: entry_64.S: use more understandable constants
Date
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 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@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: X86 ML <x86@kernel.org>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: linux-kernel@vger.kernel.org
---
arch/x86/kernel/entry_64.S | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 279af0e..d84c7c7 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -163,12 +163,12 @@ 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

/*
@@ -176,7 +176,7 @@ 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

/*
@@ -685,10 +685,14 @@ 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
@@ -714,7 +718,7 @@ 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
@@ -1525,7 +1529,7 @@ 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 */

@@ -1553,7 +1557,7 @@ 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:

/*
--
1.8.1.4


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