Author: bdragon Date: Thu Sep 10 18:41:15 2020 New Revision: 365607 URL: https://svnweb.freebsd.org/changeset/base/365607
Log: [PowerPC64LE] Add LOAD_LR_NIA and RETURN_TO_NATIVE_ENDIAN defines. * 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. Modified: head/sys/powerpc/include/asm.h Modified: head/sys/powerpc/include/asm.h ============================================================================== --- head/sys/powerpc/include/asm.h Thu Sep 10 18:27:52 2020 (r365606) +++ head/sys/powerpc/include/asm.h Thu Sep 10 18:41:15 2020 (r365607) @@ -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 _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
