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77f48ec28e
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 - i.e. to macrify the affected block.
As a result GCC considers the inline assembly block as a single instruction.
This patch handles the LOCK prefix, allowing more aggresive inlining:
text data bss dec hex filename
18140140 10225284 2957312 31322736 1ddf270 ./vmlinux before
18146889 10225380 2957312 31329581 1de0d2d ./vmlinux after (+6845)
This is the reduction in non-inlined functions:
Before: 40286
After: 40218 (-68)
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: 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/20181003213100.189959-6-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
235 lines
8.2 KiB
C
235 lines
8.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_ALTERNATIVE_H
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#define _ASM_X86_ALTERNATIVE_H
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#ifndef __ASSEMBLY__
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#include <linux/types.h>
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#include <linux/stddef.h>
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#include <linux/stringify.h>
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#include <asm/asm.h>
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/*
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* Alternative inline assembly for SMP.
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*
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* The LOCK_PREFIX macro defined here replaces the LOCK and
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* LOCK_PREFIX macros used everywhere in the source tree.
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*
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* SMP alternatives use the same data structures as the other
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* alternatives and the X86_FEATURE_UP flag to indicate the case of a
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* UP system running a SMP kernel. The existing apply_alternatives()
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* works fine for patching a SMP kernel for UP.
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*
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* The SMP alternative tables can be kept after boot and contain both
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* UP and SMP versions of the instructions to allow switching back to
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* SMP at runtime, when hotplugging in a new CPU, which is especially
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* useful in virtualized environments.
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*
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* The very common lock prefix is handled as special case in a
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* separate table which is a pure address list without replacement ptr
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* and size information. That keeps the table sizes small.
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*/
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#ifdef CONFIG_SMP
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#define LOCK_PREFIX_HERE "LOCK_PREFIX_HERE\n\t"
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#define LOCK_PREFIX "LOCK_PREFIX "
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#else /* ! CONFIG_SMP */
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#define LOCK_PREFIX_HERE ""
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#define LOCK_PREFIX ""
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#endif
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struct alt_instr {
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s32 instr_offset; /* original instruction */
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s32 repl_offset; /* offset to replacement instruction */
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u16 cpuid; /* cpuid bit set for replacement */
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u8 instrlen; /* length of original instruction */
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u8 replacementlen; /* length of new instruction */
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u8 padlen; /* length of build-time padding */
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} __packed;
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/*
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* Debug flag that can be tested to see whether alternative
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* instructions were patched in already:
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*/
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extern int alternatives_patched;
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extern void alternative_instructions(void);
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extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
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struct module;
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#ifdef CONFIG_SMP
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extern void alternatives_smp_module_add(struct module *mod, char *name,
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void *locks, void *locks_end,
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void *text, void *text_end);
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extern void alternatives_smp_module_del(struct module *mod);
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extern void alternatives_enable_smp(void);
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extern int alternatives_text_reserved(void *start, void *end);
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extern bool skip_smp_alternatives;
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#else
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static inline void alternatives_smp_module_add(struct module *mod, char *name,
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void *locks, void *locks_end,
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void *text, void *text_end) {}
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static inline void alternatives_smp_module_del(struct module *mod) {}
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static inline void alternatives_enable_smp(void) {}
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static inline int alternatives_text_reserved(void *start, void *end)
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{
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return 0;
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}
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#endif /* CONFIG_SMP */
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#define b_replacement(num) "664"#num
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#define e_replacement(num) "665"#num
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#define alt_end_marker "663"
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#define alt_slen "662b-661b"
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#define alt_pad_len alt_end_marker"b-662b"
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#define alt_total_slen alt_end_marker"b-661b"
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#define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f"
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#define __OLDINSTR(oldinstr, num) \
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"661:\n\t" oldinstr "\n662:\n" \
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".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \
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"((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
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#define OLDINSTR(oldinstr, num) \
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__OLDINSTR(oldinstr, num) \
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alt_end_marker ":\n"
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/*
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* gas compatible max based on the idea from:
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* http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
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*
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* The additional "-" is needed because gas uses a "true" value of -1.
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*/
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#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
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/*
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* Pad the second replacement alternative with additional NOPs if it is
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* additionally longer than the first replacement alternative.
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*/
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#define OLDINSTR_2(oldinstr, num1, num2) \
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"661:\n\t" oldinstr "\n662:\n" \
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".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
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"(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
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alt_end_marker ":\n"
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#define ALTINSTR_ENTRY(feature, num) \
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" .long 661b - .\n" /* label */ \
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" .long " b_replacement(num)"f - .\n" /* new instruction */ \
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" .word " __stringify(feature) "\n" /* feature bit */ \
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" .byte " alt_total_slen "\n" /* source len */ \
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" .byte " alt_rlen(num) "\n" /* replacement len */ \
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" .byte " alt_pad_len "\n" /* pad len */
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#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \
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b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
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/* alternative assembly primitive: */
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#define ALTERNATIVE(oldinstr, newinstr, feature) \
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OLDINSTR(oldinstr, 1) \
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".pushsection .altinstructions,\"a\"\n" \
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ALTINSTR_ENTRY(feature, 1) \
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".popsection\n" \
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".pushsection .altinstr_replacement, \"ax\"\n" \
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ALTINSTR_REPLACEMENT(newinstr, feature, 1) \
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".popsection\n"
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#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
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OLDINSTR_2(oldinstr, 1, 2) \
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".pushsection .altinstructions,\"a\"\n" \
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ALTINSTR_ENTRY(feature1, 1) \
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ALTINSTR_ENTRY(feature2, 2) \
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".popsection\n" \
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".pushsection .altinstr_replacement, \"ax\"\n" \
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ALTINSTR_REPLACEMENT(newinstr1, feature1, 1) \
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ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
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".popsection\n"
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/*
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* Alternative instructions for different CPU types or capabilities.
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*
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* This allows to use optimized instructions even on generic binary
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* kernels.
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*
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* length of oldinstr must be longer or equal the length of newinstr
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* It can be padded with nops as needed.
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*
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* For non barrier like inlines please define new variants
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* without volatile and memory clobber.
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*/
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#define alternative(oldinstr, newinstr, feature) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
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#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
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asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
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/*
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* Alternative inline assembly with input.
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*
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* Pecularities:
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* No memory clobber here.
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* Argument numbers start with 1.
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* Best is to use constraints that are fixed size (like (%1) ... "r")
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* If you use variable sized constraints like "m" or "g" in the
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* replacement make sure to pad to the worst case length.
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* Leaving an unused argument 0 to keep API compatibility.
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*/
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#define alternative_input(oldinstr, newinstr, feature, input...) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
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: : "i" (0), ## input)
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/*
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* This is similar to alternative_input. But it has two features and
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* respective instructions.
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*
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* If CPU has feature2, newinstr2 is used.
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* Otherwise, if CPU has feature1, newinstr1 is used.
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* Otherwise, oldinstr is used.
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*/
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#define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2, \
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feature2, input...) \
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asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, \
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newinstr2, feature2) \
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: : "i" (0), ## input)
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/* Like alternative_input, but with a single output argument */
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#define alternative_io(oldinstr, newinstr, feature, output, input...) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
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: output : "i" (0), ## input)
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/* Like alternative_io, but for replacing a direct call with another one. */
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#define alternative_call(oldfunc, newfunc, feature, output, input...) \
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asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
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: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
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/*
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* Like alternative_call, but there are two features and respective functions.
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* If CPU has feature2, function2 is used.
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* Otherwise, if CPU has feature1, function1 is used.
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* Otherwise, old function is used.
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*/
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#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
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output, input...) \
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asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
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"call %P[new2]", feature2) \
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: output, ASM_CALL_CONSTRAINT \
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: [old] "i" (oldfunc), [new1] "i" (newfunc1), \
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[new2] "i" (newfunc2), ## input)
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/*
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* use this macro(s) if you need more than one output parameter
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* in alternative_io
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*/
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#define ASM_OUTPUT2(a...) a
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/*
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* use this macro if you need clobbers but no inputs in
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* alternative_{input,io,call}()
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*/
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#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_X86_ALTERNATIVE_H */
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