9e1725b410
As described in:
77b0bf55bc: ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs")
GCC's inlining heuristics are broken with common asm() patterns used in
kernel code, resulting in the effective disabling of inlining.
The workaround is to set an assembly macro and call it from the inline
assembly block. As a result GCC considers the inline assembly block as
a single instruction. (Which it isn't, but that's the best we can get.)
This patch allows GCC to inline simple functions such as __get_seccomp_filter().
To no-one's surprise the result is that GCC performs more aggressive (read: correct)
inlining decisions in these senarios, which reduces the kernel size and presumably
also speeds it up:
text data bss dec hex filename
18140970 10225412 2957312 31323694 1ddf62e ./vmlinux before
18140140 10225284 2957312 31322736 1ddf270 ./vmlinux after (-958)
16 fewer static text symbols:
Before: 40302
After: 40286 (-16)
these got inlined instead.
Functions such as kref_get(), free_user(), fuse_file_get() now get inlined. Hurray!
[ mingo: Rewrote the changelog. ]
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181003213100.189959-5-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
127 lines
3.1 KiB
C
127 lines
3.1 KiB
C
#ifndef __ASM_X86_REFCOUNT_H
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#define __ASM_X86_REFCOUNT_H
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/*
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* x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
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* PaX/grsecurity.
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*/
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#ifdef __ASSEMBLY__
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#include <asm/asm.h>
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#include <asm/bug.h>
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.macro REFCOUNT_EXCEPTION counter:req
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.pushsection .text..refcount
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111: lea \counter, %_ASM_CX
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112: ud2
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ASM_UNREACHABLE
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.popsection
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113: _ASM_EXTABLE_REFCOUNT(112b, 113b)
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.endm
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/* Trigger refcount exception if refcount result is negative. */
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.macro REFCOUNT_CHECK_LT_ZERO counter:req
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js 111f
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REFCOUNT_EXCEPTION counter="\counter"
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.endm
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/* Trigger refcount exception if refcount result is zero or negative. */
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.macro REFCOUNT_CHECK_LE_ZERO counter:req
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jz 111f
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REFCOUNT_CHECK_LT_ZERO counter="\counter"
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.endm
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/* Trigger refcount exception unconditionally. */
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.macro REFCOUNT_ERROR counter:req
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jmp 111f
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REFCOUNT_EXCEPTION counter="\counter"
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.endm
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#else /* __ASSEMBLY__ */
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#include <linux/refcount.h>
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#include <asm/bug.h>
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/*
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* This is the first portion of the refcount error handling, which lives in
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* .text.unlikely, and is jumped to from the CPU flag check (in the
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* following macros). This saves the refcount value location into CX for
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* the exception handler to use (in mm/extable.c), and then triggers the
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* central refcount exception. The fixup address for the exception points
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* back to the regular execution flow in .text.
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*/
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static __always_inline void refcount_add(unsigned int i, refcount_t *r)
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{
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asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
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"REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
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: [counter] "+m" (r->refs.counter)
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: "ir" (i)
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: "cc", "cx");
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}
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static __always_inline void refcount_inc(refcount_t *r)
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{
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asm volatile(LOCK_PREFIX "incl %0\n\t"
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"REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
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: [counter] "+m" (r->refs.counter)
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: : "cc", "cx");
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}
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static __always_inline void refcount_dec(refcount_t *r)
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{
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asm volatile(LOCK_PREFIX "decl %0\n\t"
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"REFCOUNT_CHECK_LE_ZERO counter=\"%[counter]\""
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: [counter] "+m" (r->refs.counter)
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: : "cc", "cx");
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}
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static __always_inline __must_check
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bool refcount_sub_and_test(unsigned int i, refcount_t *r)
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{
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GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl",
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"REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
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r->refs.counter, "er", i, "%0", e, "cx");
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}
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static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
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{
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GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl",
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"REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
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r->refs.counter, "%0", e, "cx");
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}
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static __always_inline __must_check
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bool refcount_add_not_zero(unsigned int i, refcount_t *r)
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{
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int c, result;
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c = atomic_read(&(r->refs));
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do {
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if (unlikely(c == 0))
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return false;
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result = c + i;
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/* Did we try to increment from/to an undesirable state? */
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if (unlikely(c < 0 || c == INT_MAX || result < c)) {
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asm volatile("REFCOUNT_ERROR counter=\"%[counter]\""
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: : [counter] "m" (r->refs.counter)
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: "cc", "cx");
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break;
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}
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} while (!atomic_try_cmpxchg(&(r->refs), &c, result));
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return c != 0;
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}
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static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
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{
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return refcount_add_not_zero(1, r);
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}
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#endif /* __ASSEMBLY__ */
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#endif
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