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x86/asm: Fix inline asm call constraints for Clang 

For inline asm statements which have a CALL instruction, we list the
stack pointer as a constraint to convince GCC to ensure the frame
pointer is set up first:

  static inline void foo()
  {
	register void *__sp asm(_ASM_SP);
	asm("call bar" : "+r" (__sp))
  }

Unfortunately, that pattern causes Clang to corrupt the stack pointer.

The fix is easy: convert the stack pointer register variable to a global
variable.

It should be noted that the end result is different based on the GCC
version.  With GCC 6.4, this patch has exactly the same result as
before:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9820389		9491555		8816046		8516940
 after	9820389		9491555		8816046		8516940

With GCC 7.2, however, GCC's behavior has changed.  It now changes its
behavior based on the conversion of the register variable to a global.
That somehow convinces it to *always* set up the frame pointer before
inserting *any* inline asm.  (Therefore, listing the variable as an
output constraint is a no-op and is no longer necessary.)  It's a bit
overkill, but the performance impact should be negligible.  And in fact,
there's a nice improvement with frame pointers disabled:

	defconfig	defconfig-nofp	distro		distro-nofp
 before	9796316		9468236		9076191		8790305
 after	9796957		9464267		9076381		8785949

So in summary, while listing the stack pointer as an output constraint
is no longer necessary for newer versions of GCC, it's still needed for
older versions.

Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
zero-colors
Josh Poimboeuf 2017-09-20 16:24:33 -05:00 committed by Ingo Molnar
parent 0d0970eef3
commit f5caf621ee
13 changed files with 42 additions and 45 deletions
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3
arch/x86/include/asm/alternative.h
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@ -218,10 +218,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
output, input...) \
{ \
register void *__sp asm(_ASM_SP); \
asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
"call %P[new2]", feature2) \
: output, "+r" (__sp) \
: output, ASM_CALL_CONSTRAINT \
: [old] "i" (oldfunc), [new1] "i" (newfunc1), \
[new2] "i" (newfunc2), ## input); \
}

11
arch/x86/include/asm/asm.h
View File

@ -132,4 +132,15 @@
/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif
#ifndef __ASSEMBLY__
/*
* This output constraint should be used for any inline asm which has a "call"
* instruction. Otherwise the asm may be inserted before the frame pointer
* gets set up by the containing function. If you forget to do this, objtool
* may print a "call without frame pointer save/setup" warning.
*/
register unsigned int __asm_call_sp asm("esp");
#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)
#endif
#endif /* _ASM_X86_ASM_H */

10
arch/x86/include/asm/mshyperv.h
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@ -179,7 +179,6 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
u64 input_address = input ? virt_to_phys(input) : 0;
u64 output_address = output ? virt_to_phys(output) : 0;
u64 hv_status;
register void *__sp asm(_ASM_SP);
#ifdef CONFIG_X86_64
if (!hv_hypercall_pg)
@ -187,7 +186,7 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
__asm__ __volatile__("mov %4, %%r8\n"
"call *%5"
: "=a" (hv_status), "+r" (__sp),
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input_address)
: "r" (output_address), "m" (hv_hypercall_pg)
: "cc", "memory", "r8", "r9", "r10", "r11");
@ -202,7 +201,7 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
__asm__ __volatile__("call *%7"
: "=A" (hv_status),
"+c" (input_address_lo), "+r" (__sp)
"+c" (input_address_lo), ASM_CALL_CONSTRAINT
: "A" (control),
"b" (input_address_hi),
"D"(output_address_hi), "S"(output_address_lo),
@ -224,12 +223,11 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
{
u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
register void *__sp asm(_ASM_SP);
#ifdef CONFIG_X86_64
{
__asm__ __volatile__("call *%4"
: "=a" (hv_status), "+r" (__sp),
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input1)
: "m" (hv_hypercall_pg)
: "cc", "r8", "r9", "r10", "r11");
@ -242,7 +240,7 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
__asm__ __volatile__ ("call *%5"
: "=A"(hv_status),
"+c"(input1_lo),
"+r"(__sp)
ASM_CALL_CONSTRAINT
: "A" (control),
"b" (input1_hi),
"m" (hv_hypercall_pg)

14
arch/x86/include/asm/paravirt_types.h
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@ -459,8 +459,8 @@ int paravirt_disable_iospace(void);
*/
#ifdef CONFIG_X86_32
#define PVOP_VCALL_ARGS \
unsigned long __eax = __eax, __edx = __edx, __ecx = __ecx; \
register void *__sp asm("esp")
unsigned long __eax = __eax, __edx = __edx, __ecx = __ecx;
#define PVOP_CALL_ARGS PVOP_VCALL_ARGS
#define PVOP_CALL_ARG1(x) "a" ((unsigned long)(x))
@ -480,8 +480,8 @@ int paravirt_disable_iospace(void);
/* [re]ax isn't an arg, but the return val */
#define PVOP_VCALL_ARGS \
unsigned long __edi = __edi, __esi = __esi, \
__edx = __edx, __ecx = __ecx, __eax = __eax; \
register void *__sp asm("rsp")
__edx = __edx, __ecx = __ecx, __eax = __eax;
#define PVOP_CALL_ARGS PVOP_VCALL_ARGS
#define PVOP_CALL_ARG1(x) "D" ((unsigned long)(x))
@ -532,7 +532,7 @@ int paravirt_disable_iospace(void);
asm volatile(pre \
paravirt_alt(PARAVIRT_CALL) \
post \
: call_clbr, "+r" (__sp) \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
paravirt_clobber(clbr), \
##__VA_ARGS__ \
@ -542,7 +542,7 @@ int paravirt_disable_iospace(void);
asm volatile(pre \
paravirt_alt(PARAVIRT_CALL) \
post \
: call_clbr, "+r" (__sp) \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
paravirt_clobber(clbr), \
##__VA_ARGS__ \
@ -569,7 +569,7 @@ int paravirt_disable_iospace(void);
asm volatile(pre \
paravirt_alt(PARAVIRT_CALL) \
post \
: call_clbr, "+r" (__sp) \
: call_clbr, ASM_CALL_CONSTRAINT \
: paravirt_type(op), \
paravirt_clobber(clbr), \
##__VA_ARGS__ \

15
arch/x86/include/asm/preempt.h
View File

@ -100,19 +100,14 @@ static __always_inline bool should_resched(int preempt_offset)
#ifdef CONFIG_PREEMPT
extern asmlinkage void ___preempt_schedule(void);
# define __preempt_schedule() \
({ \
register void *__sp asm(_ASM_SP); \
asm volatile ("call ___preempt_schedule" : "+r"(__sp)); \
})
# define __preempt_schedule() \
asm volatile ("call ___preempt_schedule" : ASM_CALL_CONSTRAINT)
extern asmlinkage void preempt_schedule(void);
extern asmlinkage void ___preempt_schedule_notrace(void);
# define __preempt_schedule_notrace() \
({ \
register void *__sp asm(_ASM_SP); \
asm volatile ("call ___preempt_schedule_notrace" : "+r"(__sp)); \
})
# define __preempt_schedule_notrace() \
asm volatile ("call ___preempt_schedule_notrace" : ASM_CALL_CONSTRAINT)
extern asmlinkage void preempt_schedule_notrace(void);
#endif

6
arch/x86/include/asm/processor.h
View File

@ -677,8 +677,6 @@ static inline void sync_core(void)
* Like all of Linux's memory ordering operations, this is a
* compiler barrier as well.
*/
register void *__sp asm(_ASM_SP);
#ifdef CONFIG_X86_32
asm volatile (
"pushfl\n\t"
@ -686,7 +684,7 @@ static inline void sync_core(void)
"pushl $1f\n\t"
"iret\n\t"
"1:"
: "+r" (__sp) : : "memory");
: ASM_CALL_CONSTRAINT : : "memory");
#else
unsigned int tmp;
@ -703,7 +701,7 @@ static inline void sync_core(void)
"iretq\n\t"
UNWIND_HINT_RESTORE
"1:"
: "=&r" (tmp), "+r" (__sp) : : "cc", "memory");
: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
#endif
}

4
arch/x86/include/asm/rwsem.h
View File

@ -103,7 +103,6 @@ static inline bool __down_read_trylock(struct rw_semaphore *sem)
({ \
long tmp; \
struct rw_semaphore* ret; \
register void *__sp asm(_ASM_SP); \
\
asm volatile("# beginning down_write\n\t" \
LOCK_PREFIX " xadd %1,(%4)\n\t" \
@ -114,7 +113,8 @@ static inline bool __down_read_trylock(struct rw_semaphore *sem)
" call " slow_path "\n" \
"1:\n" \
"# ending down_write" \
: "+m" (sem->count), "=d" (tmp), "=a" (ret), "+r" (__sp) \
: "+m" (sem->count), "=d" (tmp), \
"=a" (ret), ASM_CALL_CONSTRAINT \
: "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \
: "memory", "cc"); \
ret; \

4
arch/x86/include/asm/uaccess.h
View File

@ -166,11 +166,11 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
({ \
int __ret_gu; \
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
register void *__sp asm(_ASM_SP); \
__chk_user_ptr(ptr); \
might_fault(); \
asm volatile("call __get_user_%P4" \
: "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \
: "=a" (__ret_gu), "=r" (__val_gu), \
ASM_CALL_CONSTRAINT \
: "0" (ptr), "i" (sizeof(*(ptr)))); \
(x) = (__force __typeof__(*(ptr))) __val_gu; \
__builtin_expect(__ret_gu, 0); \

5
arch/x86/include/asm/xen/hypercall.h
View File

@ -113,10 +113,9 @@ extern struct { char _entry[32]; } hypercall_page[];
register unsigned long __arg2 asm(__HYPERCALL_ARG2REG) = __arg2; \
register unsigned long __arg3 asm(__HYPERCALL_ARG3REG) = __arg3; \
register unsigned long __arg4 asm(__HYPERCALL_ARG4REG) = __arg4; \
register unsigned long __arg5 asm(__HYPERCALL_ARG5REG) = __arg5; \
register void *__sp asm(_ASM_SP);
register unsigned long __arg5 asm(__HYPERCALL_ARG5REG) = __arg5;
#define __HYPERCALL_0PARAM "=r" (__res), "+r" (__sp)
#define __HYPERCALL_0PARAM "=r" (__res), ASM_CALL_CONSTRAINT
#define __HYPERCALL_1PARAM __HYPERCALL_0PARAM, "+r" (__arg1)
#define __HYPERCALL_2PARAM __HYPERCALL_1PARAM, "+r" (__arg2)
#define __HYPERCALL_3PARAM __HYPERCALL_2PARAM, "+r" (__arg3)

3
arch/x86/kvm/emulate.c
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@ -5296,7 +5296,6 @@ static void fetch_possible_mmx_operand(struct x86_emulate_ctxt *ctxt,
static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
{
register void *__sp asm(_ASM_SP);
ulong flags = (ctxt->eflags & EFLAGS_MASK) | X86_EFLAGS_IF;
if (!(ctxt->d & ByteOp))
@ -5304,7 +5303,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
: "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
[fastop]"+S"(fop), "+r"(__sp)
[fastop]"+S"(fop), ASM_CALL_CONSTRAINT
: "c"(ctxt->src2.val));
ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) | (flags & EFLAGS_MASK);

3
arch/x86/kvm/vmx.c
View File

@ -9036,7 +9036,6 @@ static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
{
u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
register void *__sp asm(_ASM_SP);
if ((exit_intr_info & (INTR_INFO_VALID_MASK | INTR_INFO_INTR_TYPE_MASK))
== (INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR)) {
@ -9065,7 +9064,7 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
#ifdef CONFIG_X86_64
[sp]"=&r"(tmp),
#endif
"+r"(__sp)
ASM_CALL_CONSTRAINT
:
[entry]"r"(entry),
[ss]"i"(__KERNEL_DS),

3
arch/x86/mm/fault.c
View File

@ -806,7 +806,6 @@ no_context(struct pt_regs *regs, unsigned long error_code,
if (is_vmalloc_addr((void *)address) &&
(((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
register void *__sp asm("rsp");
unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *);
/*
* We're likely to be running with very little stack space
@ -821,7 +820,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
asm volatile ("movq %[stack], %%rsp\n\t"
"call handle_stack_overflow\n\t"
"1: jmp 1b"
: "+r" (__sp)
: ASM_CALL_CONSTRAINT
: "D" ("kernel stack overflow (page fault)"),
"S" (regs), "d" (address),
[stack] "rm" (stack));

6
tools/objtool/Documentation/stack-validation.txt
View File

@ -194,10 +194,10 @@ they mean, and suggestions for how to fix them.
If it's a GCC-compiled .c file, the error may be because the function
uses an inline asm() statement which has a "call" instruction. An
asm() statement with a call instruction must declare the use of the
stack pointer in its output operand. For example, on x86_64:
stack pointer in its output operand. On x86_64, this means adding
the ASM_CALL_CONSTRAINT as an output constraint:
register void *__sp asm("rsp");
asm volatile("call func" : "+r" (__sp));
asm volatile("call func" : ASM_CALL_CONSTRAINT);
Otherwise the stack frame may not get created before the call.