diff options
Diffstat (limited to 'arch/powerpc/lib/code-patching.c')
| -rw-r--r-- | arch/powerpc/lib/code-patching.c | 45 |
1 files changed, 44 insertions, 1 deletions
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index c1746df0f88e..0899315e1434 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -32,6 +32,49 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags) return patch_instruction(addr, create_branch(addr, target, flags)); } +bool is_offset_in_branch_range(long offset) +{ + /* + * Powerpc branch instruction is : + * + * 0 6 30 31 + * +---------+----------------+---+---+ + * | opcode | LI |AA |LK | + * +---------+----------------+---+---+ + * Where AA = 0 and LK = 0 + * + * LI is a signed 24 bits integer. The real branch offset is computed + * by: imm32 = SignExtend(LI:'0b00', 32); + * + * So the maximum forward branch should be: + * (0x007fffff << 2) = 0x01fffffc = 0x1fffffc + * The maximum backward branch should be: + * (0xff800000 << 2) = 0xfe000000 = -0x2000000 + */ + return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3)); +} + +/* + * Helper to check if a given instruction is a conditional branch + * Derived from the conditional checks in analyse_instr() + */ +bool __kprobes is_conditional_branch(unsigned int instr) +{ + unsigned int opcode = instr >> 26; + + if (opcode == 16) /* bc, bca, bcl, bcla */ + return true; + if (opcode == 19) { + switch ((instr >> 1) & 0x3ff) { + case 16: /* bclr, bclrl */ + case 528: /* bcctr, bcctrl */ + case 560: /* bctar, bctarl */ + return true; + } + } + return false; +} + unsigned int create_branch(const unsigned int *addr, unsigned long target, int flags) { @@ -43,7 +86,7 @@ unsigned int create_branch(const unsigned int *addr, offset = offset - (unsigned long)addr; /* Check we can represent the target in the instruction format */ - if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3) + if (!is_offset_in_branch_range(offset)) return 0; /* Mask out the flags and target, so they don't step on each other. */ |