diff options
Diffstat (limited to 'bfd/elf32-ppc.c')
| -rw-r--r-- | bfd/elf32-ppc.c | 67 |
1 files changed, 48 insertions, 19 deletions
diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c index 868fe50..61e94a0 100644 --- a/bfd/elf32-ppc.c +++ b/bfd/elf32-ppc.c @@ -9279,27 +9279,56 @@ ppc_elf_relocate_section (bfd *output_bfd, if (is_data) continue; - /* Some instructions can be left alone too. In this - category are most insns that unconditionally change - control flow, and isync. Of these, some *must* be left - alone, for example, the "bcl 20, 31, label" used in pic - sequences to give the address of the next insn. twui - and twu apparently are not safe. */ + /* Some instructions can be left alone too. Unconditional + branches, except for bcctr with BO=0x14 (bctr, bctrl), + avoid the icache failure. + + The problem occurs due to prefetch across a page boundary + where stale instructions can be fetched from the next + page, and the mechanism for flushing these bad + instructions fails under certain circumstances. The + unconditional branches: + 1) Branch: b, bl, ba, bla, + 2) Branch Conditional: bc, bca, bcl, bcla, + 3) Branch Conditional to Link Register: bclr, bclrl, + where (2) and (3) have BO=0x14 making them unconditional, + prevent the bad prefetch because the prefetch itself is + affected by these instructions. This happens even if the + instruction is not executed. + + A bctr example: + . + . lis 9,new_page@ha + . addi 9,9,new_page@l + . mtctr 9 + . bctr + . nop + . nop + . new_page: + . + The bctr is not predicted taken due to ctr not being + ready, so prefetch continues on past the bctr into the + new page which might have stale instructions. If they + fail to be flushed, then they will be executed after the + bctr executes. Either of the following modifications + prevent the bad prefetch from happening in the first + place: + . + . lis 9,new_page@ha lis 9,new_page@ha + . addi 9,9,new_page@l addi 9,9,new_page@l + . mtctr 9 mtctr 9 + . bctr bctr + . nop b somewhere_else + . b somewhere_else nop + . new_page: new_page: + . */ insn = bfd_get_32 (input_bfd, contents + offset); - if (insn == 0 - || (insn & (0x3f << 26)) == (18u << 26) /* b */ - || ((insn & (0x3f << 26)) == (16u << 26) /* bc always */ - && (insn & (0x14 << 21)) == (0x14 << 21)) - || ((insn & (0x3f << 26)) == (19u << 26) /* blr, bctr */ - && (insn & (0x14 << 21)) == (0x14 << 21) - && (insn & (0x1ff << 1)) == (16u << 1)) - || (insn & (0x3f << 26)) == (17u << 26) /* sc */ + if ((insn & (0x3f << 26)) == (18u << 26) /* b,bl,ba,bla */ + || ((insn & (0x3f << 26)) == (16u << 26) /* bc,bcl,bca,bcla*/ + && (insn & (0x14 << 21)) == (0x14 << 21)) /* with BO=0x14 */ || ((insn & (0x3f << 26)) == (19u << 26) - && ((insn & (0x3ff << 1)) == (38u << 1) /* rfmci */ - || (insn & (0x3ff << 1)) == (50u << 1) /* rfi */ - || (insn & (0x3ff << 1)) == (51u << 1) /* rfci */ - || (insn & (0x3ff << 1)) == (82u << 1) /* rfsvc */ - || (insn & (0x3ff << 1)) == (150u << 1))) /* isync */) + && (insn & (0x3ff << 1)) == (16u << 1) /* bclr,bclrl */ + && (insn & (0x14 << 21)) == (0x14 << 21)))/* with BO=0x14 */ continue; patch_addr = (start_addr + input_section->size |