3rd-party/linux-kernel-module-cheat
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x86 asm: move cmp from x86-assembly-cheat

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Ciro Santilli 六四事件 法轮功
2019-06-12 00:00:01 +00:00
parent 0028ff0ebd
commit cefb1a823d
3 changed files with 36 additions and 0 deletions
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1
README.adoc
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@@ -12364,6 +12364,7 @@ Bibliography:
** link:userland/arch/x86_64/div_overflow.S[DIV overflow] ** link:userland/arch/x86_64/div_overflow.S[DIV overflow]
** link:userland/arch/x86_64/div_zero.S[DIV zero] ** link:userland/arch/x86_64/div_zero.S[DIV zero]
** link:userland/arch/x86_64/idiv.S[IDIV] ** link:userland/arch/x86_64/idiv.S[IDIV]
* link:userland/arch/x86_64/cmp.S[CMP]
=== x86 SIMD === x86 SIMD

14
userland/arch/x86_64/add.S
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@@ -42,4 +42,18 @@ LKMC_PROLOGUE
*/ */
addq memory_immediate, memory_register addq memory_immediate, memory_register
#endif #endif
/* ADD and many other instructions automatically update the status flags
* which controls branches.
*/
/* Equals 0. */
mov $1, %rax
add $-1, %rax
LKMC_ASSERT(je)
/* Not equals 0. */
mov $2, %rax
add $-1, %rax
LKMC_ASSERT(jne)
LKMC_EPILOGUE LKMC_EPILOGUE

21
userland/arch/x86_64/cmp.S Normal file
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@@ -0,0 +1,21 @@
/* https://github.com/cirosantilli/linux-kernel-module-cheat#userland-assembly
*
* Compare two numbers and set the flags register.
*
* `cmp X, Y` does `X - Y` and ignores the exact result, but sets
* all flags that would be set on the subtraction, just like SUB does.
*/
#include <lkmc.h>
LKMC_PROLOGUE
/* 2 == 2 */
mov $2, %rax
cmp $2, %rax
LKMC_ASSERT(je)
/* 2 > 1 */
mov $2, %rax
cmp $1, %rax
LKMC_ASSERT(ja)
LKMC_EPILOGUE