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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>
147 lines
3.8 KiB
C
147 lines
3.8 KiB
C
#ifndef _ASM_X86_ASM_H
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#define _ASM_X86_ASM_H
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#ifdef __ASSEMBLY__
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# define __ASM_FORM(x) x
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# define __ASM_FORM_RAW(x) x
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# define __ASM_FORM_COMMA(x) x,
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#else
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# define __ASM_FORM(x) " " #x " "
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# define __ASM_FORM_RAW(x) #x
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# define __ASM_FORM_COMMA(x) " " #x ","
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#endif
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#ifdef CONFIG_X86_32
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# define __ASM_SEL(a,b) __ASM_FORM(a)
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# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(a)
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#else
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# define __ASM_SEL(a,b) __ASM_FORM(b)
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# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(b)
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#endif
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#define __ASM_SIZE(inst, ...) __ASM_SEL(inst##l##__VA_ARGS__, \
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inst##q##__VA_ARGS__)
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#define __ASM_REG(reg) __ASM_SEL_RAW(e##reg, r##reg)
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#define _ASM_PTR __ASM_SEL(.long, .quad)
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#define _ASM_ALIGN __ASM_SEL(.balign 4, .balign 8)
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#define _ASM_MOV __ASM_SIZE(mov)
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#define _ASM_INC __ASM_SIZE(inc)
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#define _ASM_DEC __ASM_SIZE(dec)
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#define _ASM_ADD __ASM_SIZE(add)
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#define _ASM_SUB __ASM_SIZE(sub)
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#define _ASM_XADD __ASM_SIZE(xadd)
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#define _ASM_MUL __ASM_SIZE(mul)
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#define _ASM_AX __ASM_REG(ax)
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#define _ASM_BX __ASM_REG(bx)
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#define _ASM_CX __ASM_REG(cx)
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#define _ASM_DX __ASM_REG(dx)
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#define _ASM_SP __ASM_REG(sp)
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#define _ASM_BP __ASM_REG(bp)
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#define _ASM_SI __ASM_REG(si)
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#define _ASM_DI __ASM_REG(di)
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/*
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* Macros to generate condition code outputs from inline assembly,
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* The output operand must be type "bool".
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*/
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#ifdef __GCC_ASM_FLAG_OUTPUTS__
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# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
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# define CC_OUT(c) "=@cc" #c
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#else
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# define CC_SET(c) "\n\tset" #c " %[_cc_" #c "]\n"
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# define CC_OUT(c) [_cc_ ## c] "=qm"
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#endif
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/* Exception table entry */
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#ifdef __ASSEMBLY__
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# define _ASM_EXTABLE_HANDLE(from, to, handler) \
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.pushsection "__ex_table","a" ; \
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.balign 4 ; \
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.long (from) - . ; \
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.long (to) - . ; \
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.long (handler) - . ; \
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.popsection
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# define _ASM_EXTABLE(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
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# define _ASM_EXTABLE_FAULT(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
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# define _ASM_EXTABLE_EX(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
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# define _ASM_EXTABLE_REFCOUNT(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
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# define _ASM_NOKPROBE(entry) \
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.pushsection "_kprobe_blacklist","aw" ; \
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_ASM_ALIGN ; \
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_ASM_PTR (entry); \
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.popsection
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.macro ALIGN_DESTINATION
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/* check for bad alignment of destination */
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movl %edi,%ecx
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andl $7,%ecx
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jz 102f /* already aligned */
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subl $8,%ecx
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negl %ecx
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subl %ecx,%edx
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100: movb (%rsi),%al
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101: movb %al,(%rdi)
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incq %rsi
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incq %rdi
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decl %ecx
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jnz 100b
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102:
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.section .fixup,"ax"
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103: addl %ecx,%edx /* ecx is zerorest also */
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jmp copy_user_handle_tail
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.previous
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_ASM_EXTABLE(100b,103b)
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_ASM_EXTABLE(101b,103b)
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.endm
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#else
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# define _EXPAND_EXTABLE_HANDLE(x) #x
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# define _ASM_EXTABLE_HANDLE(from, to, handler) \
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" .pushsection \"__ex_table\",\"a\"\n" \
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" .balign 4\n" \
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" .long (" #from ") - .\n" \
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" .long (" #to ") - .\n" \
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" .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n" \
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" .popsection\n"
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# define _ASM_EXTABLE(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
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# define _ASM_EXTABLE_FAULT(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
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# define _ASM_EXTABLE_EX(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
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# define _ASM_EXTABLE_REFCOUNT(from, to) \
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_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
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/* For C file, we already have NOKPROBE_SYMBOL macro */
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#endif
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#ifndef __ASSEMBLY__
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/*
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* This output constraint should be used for any inline asm which has a "call"
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* instruction. Otherwise the asm may be inserted before the frame pointer
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* gets set up by the containing function. If you forget to do this, objtool
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* may print a "call without frame pointer save/setup" warning.
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*/
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register unsigned int __asm_call_sp asm("esp");
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#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)
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#endif
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#endif /* _ASM_X86_ASM_H */
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