[PATCH v2 6/8] x86/entry: add unwind hint annotations

From: Josh Poimboeuf
Date: Wed Jun 28 2017 - 11:13:26 EST

Add unwind hint annotations to entry_64.S. This will enable the undwarf
unwinder to unwind through any location in the entry code including
syscalls, interrupts, and exceptions.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
arch/x86/entry/Makefile | 1 -
arch/x86/entry/calling.h | 6 +++++
arch/x86/entry/entry_64.S | 56 ++++++++++++++++++++++++++++++++++++++++++-----
3 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index 9976fce..af28a8a 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -2,7 +2,6 @@
# Makefile for the x86 low level entry code
#

-OBJECT_FILES_NON_STANDARD_entry_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_entry_64_compat.o := y

CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,)
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 05ed3d3..4050b73 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -1,4 +1,6 @@
#include <linux/jump_label.h>
+#include <asm/undwarf.h>
+

/*

@@ -112,6 +114,7 @@ For 32-bit we have the following conventions - kernel is built with
movq %rdx, 12*8+\offset(%rsp)
movq %rsi, 13*8+\offset(%rsp)
movq %rdi, 14*8+\offset(%rsp)
+ UNWIND_HINT_REGS offset=\offset extra=0
.endm
.macro SAVE_C_REGS offset=0
SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1
@@ -136,6 +139,7 @@ For 32-bit we have the following conventions - kernel is built with
movq %r12, 3*8+\offset(%rsp)
movq %rbp, 4*8+\offset(%rsp)
movq %rbx, 5*8+\offset(%rsp)
+ UNWIND_HINT_REGS offset=\offset
.endm

.macro RESTORE_EXTRA_REGS offset=0
@@ -145,6 +149,7 @@ For 32-bit we have the following conventions - kernel is built with
movq 3*8+\offset(%rsp), %r12
movq 4*8+\offset(%rsp), %rbp
movq 5*8+\offset(%rsp), %rbx
+ UNWIND_HINT_REGS offset=\offset extra=0
.endm

.macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1
@@ -167,6 +172,7 @@ For 32-bit we have the following conventions - kernel is built with
.endif
movq 13*8(%rsp), %rsi
movq 14*8(%rsp), %rdi
+ UNWIND_HINT_IRET_REGS offset=16*8
.endm
.macro RESTORE_C_REGS
RESTORE_C_REGS_HELPER 1,1,1,1,1
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index a9a8027..9075a6c 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -36,6 +36,7 @@
#include <asm/smap.h>
#include <asm/pgtable_types.h>
#include <asm/export.h>
+#include <asm/frame.h>
#include <linux/err.h>

.code64
@@ -43,9 +44,10 @@

#ifdef CONFIG_PARAVIRT
ENTRY(native_usergs_sysret64)
+ UNWIND_HINT_EMPTY
swapgs
sysretq
-ENDPROC(native_usergs_sysret64)
+END(native_usergs_sysret64)
#endif /* CONFIG_PARAVIRT */

.macro TRACE_IRQS_IRETQ
@@ -134,6 +136,7 @@ ENDPROC(native_usergs_sysret64)
*/

ENTRY(entry_SYSCALL_64)
+ UNWIND_HINT_EMPTY
/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
@@ -169,6 +172,7 @@ GLOBAL(entry_SYSCALL_64_after_swapgs)
pushq %r10 /* pt_regs->r10 */
pushq %r11 /* pt_regs->r11 */
sub $(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */
+ UNWIND_HINT_REGS extra=0

/*
* If we need to do entry work or if we guess we'll need to do
@@ -223,6 +227,7 @@ entry_SYSCALL_64_fastpath:
movq EFLAGS(%rsp), %r11
RESTORE_C_REGS_EXCEPT_RCX_R11
movq RSP(%rsp), %rsp
+ UNWIND_HINT_EMPTY
USERGS_SYSRET64

1:
@@ -316,6 +321,7 @@ syscall_return_via_sysret:
/* rcx and r11 are already restored (see code above) */
RESTORE_C_REGS_EXCEPT_RCX_R11
movq RSP(%rsp), %rsp
+ UNWIND_HINT_EMPTY
USERGS_SYSRET64

opportunistic_sysret_failed:
@@ -343,6 +349,7 @@ ENTRY(stub_ptregs_64)
DISABLE_INTERRUPTS(CLBR_ANY)
TRACE_IRQS_OFF
popq %rax
+ UNWIND_HINT_REGS extra=0
jmp entry_SYSCALL64_slow_path

1:
@@ -351,6 +358,7 @@ END(stub_ptregs_64)

.macro ptregs_stub func
ENTRY(ptregs_\func)
+ UNWIND_HINT_FUNC
leaq \func(%rip), %rax
jmp stub_ptregs_64
END(ptregs_\func)
@@ -367,6 +375,7 @@ END(ptregs_\func)
* %rsi: next task
*/
ENTRY(__switch_to_asm)
+ UNWIND_HINT_FUNC
/*
* Save callee-saved registers
* This must match the order in inactive_task_frame
@@ -406,6 +415,7 @@ END(__switch_to_asm)
* r12: kernel thread arg
*/
ENTRY(ret_from_fork)
+ UNWIND_HINT_EMPTY
movq %rax, %rdi
call schedule_tail /* rdi: 'prev' task parameter */

@@ -413,6 +423,7 @@ ENTRY(ret_from_fork)
jnz 1f /* kernel threads are uncommon */

2:
+ UNWIND_HINT_REGS
movq %rsp, %rdi
call syscall_return_slowpath /* returns with IRQs disabled */
TRACE_IRQS_ON /* user mode is traced as IRQS on */
@@ -440,10 +451,11 @@ END(ret_from_fork)
ENTRY(irq_entries_start)
vector=FIRST_EXTERNAL_VECTOR
.rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
+ UNWIND_HINT_IRET_REGS
pushq $(~vector+0x80) /* Note: always in signed byte range */
- vector=vector+1
jmp common_interrupt
.align 8
+ vector=vector+1
.endr
END(irq_entries_start)

@@ -495,7 +507,9 @@ END(irq_entries_start)
movq %rsp, %rdi
incl PER_CPU_VAR(irq_count)
cmovzq PER_CPU_VAR(irq_stack_ptr), %rsp
+ UNWIND_HINT_REGS base=rdi
pushq %rdi
+ UNWIND_HINT_REGS indirect=1
/* We entered an interrupt context - irqs are off: */
TRACE_IRQS_OFF

@@ -519,6 +533,7 @@ ret_from_intr:

/* Restore saved previous stack */
popq %rsp
+ UNWIND_HINT_REGS

testb $3, CS(%rsp)
jz retint_kernel
@@ -561,6 +576,7 @@ restore_c_regs_and_iret:
INTERRUPT_RETURN

ENTRY(native_iret)
+ UNWIND_HINT_IRET_REGS
/*
* Are we returning to a stack segment from the LDT? Note: in
* 64-bit mode SS:RSP on the exception stack is always valid.
@@ -633,6 +649,7 @@ native_irq_return_ldt:
orq PER_CPU_VAR(espfix_stack), %rax
SWAPGS
movq %rax, %rsp
+ UNWIND_HINT_IRET_REGS offset=8

/*
* At this point, we cannot write to the stack any more, but we can
@@ -654,6 +671,7 @@ END(common_interrupt)
*/
.macro apicinterrupt3 num sym do_sym
ENTRY(\sym)
+ UNWIND_HINT_IRET_REGS
ASM_CLAC
pushq $~(\num)
.Lcommon_\sym:
@@ -739,6 +757,8 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt

.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
ENTRY(\sym)
+ UNWIND_HINT_IRET_REGS offset=8
+
/* Sanity check */
.if \shift_ist != -1 && \paranoid == 0
.error "using shift_ist requires paranoid=1"
@@ -762,6 +782,7 @@ ENTRY(\sym)
.else
call error_entry
.endif
+ UNWIND_HINT_REGS
/* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */

.if \paranoid
@@ -859,6 +880,7 @@ idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0
* edi: new selector
*/
ENTRY(native_load_gs_index)
+ FRAME_BEGIN
pushfq
DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
SWAPGS
@@ -867,8 +889,9 @@ ENTRY(native_load_gs_index)
2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
SWAPGS
popfq
+ FRAME_END
ret
-END(native_load_gs_index)
+ENDPROC(native_load_gs_index)
EXPORT_SYMBOL(native_load_gs_index)

_ASM_EXTABLE(.Lgs_change, bad_gs)
@@ -898,7 +921,7 @@ ENTRY(do_softirq_own_stack)
leaveq
decl PER_CPU_VAR(irq_count)
ret
-END(do_softirq_own_stack)
+ENDPROC(do_softirq_own_stack)

#ifdef CONFIG_XEN
idtentry xen_hypervisor_callback xen_do_hypervisor_callback has_error_code=0
@@ -922,13 +945,18 @@ ENTRY(xen_do_hypervisor_callback) /* do_hypervisor_callback(struct *pt_regs) */
* Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
* see the correct pointer to the pt_regs
*/
+ UNWIND_HINT_FUNC
movq %rdi, %rsp /* we don't return, adjust the stack frame */
+ UNWIND_HINT_REGS
11: incl PER_CPU_VAR(irq_count)
movq %rsp, %rbp
cmovzq PER_CPU_VAR(irq_stack_ptr), %rsp
+ UNWIND_HINT_REGS base=rbp
pushq %rbp /* frame pointer backlink */
+ UNWIND_HINT_REGS indirect=1
call xen_evtchn_do_upcall
popq %rsp
+ UNWIND_HINT_REGS
decl PER_CPU_VAR(irq_count)
#ifndef CONFIG_PREEMPT
call xen_maybe_preempt_hcall
@@ -950,6 +978,7 @@ END(xen_do_hypervisor_callback)
* with its current contents: any discrepancy means we in category 1.
*/
ENTRY(xen_failsafe_callback)
+ UNWIND_HINT_EMPTY
movl %ds, %ecx
cmpw %cx, 0x10(%rsp)
jne 1f
@@ -969,11 +998,13 @@ ENTRY(xen_failsafe_callback)
pushq $0 /* RIP */
pushq %r11
pushq %rcx
+ UNWIND_HINT_IRET_REGS offset=8
jmp general_protection
1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
movq (%rsp), %rcx
movq 8(%rsp), %r11
addq $0x30, %rsp
+ UNWIND_HINT_IRET_REGS
pushq $-1 /* orig_ax = -1 => not a system call */
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
@@ -1019,6 +1050,7 @@ idtentry machine_check has_error_code=0 paranoid=1 do_sym=*machine_check_vec
* Return: ebx=0: need swapgs on exit, ebx=1: otherwise
*/
ENTRY(paranoid_entry)
+ UNWIND_HINT_FUNC
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
@@ -1046,6 +1078,7 @@ END(paranoid_entry)
* On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
*/
ENTRY(paranoid_exit)
+ UNWIND_HINT_REGS
DISABLE_INTERRUPTS(CLBR_ANY)
TRACE_IRQS_OFF_DEBUG
testl %ebx, %ebx /* swapgs needed? */
@@ -1067,6 +1100,7 @@ END(paranoid_exit)
* Return: EBX=0: came from user mode; EBX=1: otherwise
*/
ENTRY(error_entry)
+ UNWIND_HINT_FUNC
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
@@ -1151,6 +1185,7 @@ END(error_entry)
* 0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode
*/
ENTRY(error_exit)
+ UNWIND_HINT_REGS
DISABLE_INTERRUPTS(CLBR_ANY)
TRACE_IRQS_OFF
testl %ebx, %ebx
@@ -1160,6 +1195,7 @@ END(error_exit)

/* Runs on exception stack */
ENTRY(nmi)
+ UNWIND_HINT_IRET_REGS
/*
* Fix up the exception frame if we're on Xen.
* PARAVIRT_ADJUST_EXCEPTION_FRAME is guaranteed to push at most
@@ -1231,11 +1267,13 @@ ENTRY(nmi)
cld
movq %rsp, %rdx
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
+ UNWIND_HINT_IRET_REGS base=rdx offset=8
pushq 5*8(%rdx) /* pt_regs->ss */
pushq 4*8(%rdx) /* pt_regs->rsp */
pushq 3*8(%rdx) /* pt_regs->flags */
pushq 2*8(%rdx) /* pt_regs->cs */
pushq 1*8(%rdx) /* pt_regs->rip */
+ UNWIND_HINT_IRET_REGS
pushq $-1 /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
@@ -1252,6 +1290,7 @@ ENTRY(nmi)
pushq %r13 /* pt_regs->r13 */
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
+ UNWIND_HINT_REGS
ENCODE_FRAME_POINTER

/*
@@ -1406,6 +1445,7 @@ first_nmi:
.rept 5
pushq 11*8(%rsp)
.endr
+ UNWIND_HINT_IRET_REGS

/* Everything up to here is safe from nested NMIs */

@@ -1421,6 +1461,7 @@ first_nmi:
pushq $__KERNEL_CS /* CS */
pushq $1f /* RIP */
INTERRUPT_RETURN /* continues at repeat_nmi below */
+ UNWIND_HINT_IRET_REGS
1:
#endif

@@ -1470,6 +1511,7 @@ end_repeat_nmi:
* exceptions might do.
*/
call paranoid_entry
+ UNWIND_HINT_REGS

/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
movq %rsp, %rdi
@@ -1507,17 +1549,19 @@ nmi_restore:
END(nmi)

ENTRY(ignore_sysret)
+ UNWIND_HINT_EMPTY
mov $-ENOSYS, %eax
sysret
END(ignore_sysret)

ENTRY(rewind_stack_do_exit)
+ UNWIND_HINT_FUNC
/* Prevent any naive code from trying to unwind to our caller. */
xorl %ebp, %ebp

movq PER_CPU_VAR(cpu_current_top_of_stack), %rax
- leaq -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%rax), %rsp
+ leaq -PTREGS_SIZE(%rax), %rsp
+ UNWIND_HINT_FUNC cfa_offset=PTREGS_SIZE

call do_exit
-1: jmp 1b
END(rewind_stack_do_exit)
--
2.7.5