3rd-party/linux-kernel-module-cheat
1
0
Fork 0
mirror of https://github.com/cirosantilli/linux-kernel-module-cheat.git synced 2026-01-23 02:05:57 +01:00
Code Issues Releases Wiki Activity

x86 asm: move jcc from x86-assembly-cheat

Browse Source
This commit is contained in:
Ciro Santilli 六四事件 法轮功
2019-06-15 00:00:00 +00:00
parent 647eacf13a
commit 58418b2a8d
2 changed files with 87 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
README.adoc
View File

@@ -12382,6 +12382,31 @@ Bibliography:
* link:userland/arch/x86_64/jmp.S[JMP] * link:userland/arch/x86_64/jmp.S[JMP]
** link:userland/arch/x86_64/jmp_indirect.S[JMP indirect] ** link:userland/arch/x86_64/jmp_indirect.S[JMP indirect]
==== x86 Jcc instructions
link:userland/arch/x86_64/jcc.S[Jcc]
Jump if certain conditions of the flags register are met.
Jcc includes the instructions:
* JZ, JNZ
** JE, JNE: same as JZ, with two separate manual entries that say almost the same thing, lol: https://stackoverflow.com/questions/14267081/difference-between-je-jne-and-jz-jnz/14267662#14267662
* JG: greater than, signed
** JA: Above: greater than, unsigned
* JL: less than, signed
** JB below: less than, unsigned
* JC: carry
* JO: overflow
* JP: parity. Why it exists: https://stackoverflow.com/questions/25707130/what-is-the-purpose-of-the-parity-flag-on-a-cpu
* JPE: parity even
* JPO: parity odd
JG vs JA and JL vs JB:
* https://stackoverflow.com/questions/20906639/difference-between-ja-and-jg-in-assembly
* https://stackoverflow.com/questions/9617877/assembly-jg-jnle-jl-jnge-after-cmp
=== x86 SIMD === x86 SIMD
History: History:

62
userland/arch/x86_64/jcc.S Normal file
View File

@@ -0,0 +1,62 @@
/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-jcc-instructions */
#include <lkmc.h>
LKMC_PROLOGUE
/* JZ, JE */
mov $1, %r12
cmp $1, %r12
LKMC_ASSERT(jz)
cmp $2, %r12
LKMC_ASSERT(jnz)
/* JA, JB, JG, JL */
/* 0x0 ==
*
* * 0 in 2's complement signed
* * 0 in 2's complement unsigned
*/
mov $0, %al
/* 0xFF ==
*
* * -1 in 2's complement signed
* * 255 in 2's complement unsigned
*/
mov $0xFF, %bl
/* Do the operation. */
cmp %bl, %al
/* We push and pop flags with PUSHF and POPF because
* our assert function might change them. All comparisons
* are done with the flags of the original cmp operation.
*
* We push twice to keep the stack aligned to 16 bits
* when calling our C asset function.
*/
pushf
pushf
/* 0 < 255 */
LKMC_ASSERT(jb)
popf
pushf
/* ! 0 > 255 */
LKMC_ASSERT(jna)
popf
pushf
/* ! 0 < -1 */
LKMC_ASSERT(jnl)
popf
pushf
/* 0 > -1 */
LKMC_ASSERT(jg)
/* Restore stack. */
add $16, %rsp
LKMC_EPILOGUE