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[PowerPC64LE] Add LOAD_LR_NIA and RETURN_TO_NATIVE_ENDIAN defines.

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* Add LOAD_LR_NIA define. This is preferred to "bl 1f; 1:" because it
doesn't pollute the branch predictor.

* Add magic sequence to return the CPU to the correct endianness after
jumping to cross-endian code, similar to the sequence from Linux.

Sponsored by:	Tag1 Consulting, Inc.
This commit is contained in:
Brandon Bergren 2020-09-10 18:41:15 +00:00
parent 9f917148e0
commit 691b35f344
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=365607
1 changed files with 37 additions and 0 deletions
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37
sys/powerpc/include/asm.h
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@ -194,6 +194,43 @@ name: \
#define ASENTRY_NOPROF(y) _ENTRY(ASMNAME(y))
#define ENTRY_NOPROF(y) _ENTRY(CNAME(y))
/* Load NIA without affecting branch prediction */
#define LOAD_LR_NIA bcl 20, 31, .+4
/*
* Magic sequence to return to native endian.
* Overwrites r0 and r11.
*
* The encoding of the instruction "tdi 0, %r0, 0x48" in opposite endian
* happens to be "b . + 8". This is useful because we can write a sequence
* of instructions that can execute in either endian.
*
* Use a sequence of handcoded instructions that switches contexts to the
* instruction following the sequence, but with the correct PSL_LE bit.
*
* The same sequence works for both BE and LE because the xori will flip
* the bit to the other state, and the code only runs when running in the
* wrong endian.
*
* This sequence is NMI-reentrant.
*/
#define RETURN_TO_NATIVE_ENDIAN \
tdi 0, %r0, 0x48; /* Endian swapped: b . + 8 */\
b 1f; /* Will fall through to here if correct */\
.long 0xa600607d; /* mfmsr %r11 */\
.long 0x00000038; /* li %r0, 0 */\
.long 0x6401617d; /* mtmsrd %r0, 1 (L=1 EE,RI bits only) */\
.long 0x01006b69; /* xori %r11, %r11, 0x1 (PSL_LE) */\
.long 0xa602087c; /* mflr %r0 */\
.long 0x05009f42; /* LOAD_LR_NIA */\
.long 0xa6037b7d; /* 0: mtsrr1 %r11 */\
.long 0xa602687d; /* mflr %r11 */\
.long 0x18006b39; /* addi %r11, %r11, (1f - 0b) */\
.long 0xa6037a7d; /* mtsrr0 %r11 */\
.long 0xa603087c; /* mtlr %r0 */\
.long 0x2400004c; /* rfid */\
1: /* RETURN_TO_NATIVE_ENDIAN */
#define ASMSTR .asciz
#define RCSID(x) .text; .asciz x