arm64: alternative: Add support for patching adrp instructions

[cascardo/linux.git] / arch / arm64 / kernel / alternative.c

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index 992918d..06d650f 100644 (file)
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -58,6 +58,8 @@ static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
        BUG();
 }
 
+#define align_down(x, a)       ((unsigned long)(x) & ~(((unsigned long)(a)) - 1))
+
 static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr)
 {
        u32 insn;
@@ -79,6 +81,19 @@ static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr)
                        offset = target - (unsigned long)insnptr;
                        insn = aarch64_set_branch_offset(insn, offset);
                }
+       } else if (aarch64_insn_is_adrp(insn)) {
+               s32 orig_offset, new_offset;
+               unsigned long target;
+
+               /*
+                * If we're replacing an adrp instruction, which uses PC-relative
+                * immediate addressing, adjust the offset to reflect the new
+                * PC. adrp operates on 4K aligned addresses.
+                */
+               orig_offset  = aarch64_insn_adrp_get_offset(insn);
+               target = align_down(altinsnptr, SZ_4K) + orig_offset;
+               new_offset = target - align_down(insnptr, SZ_4K);
+               insn = aarch64_insn_adrp_set_offset(insn, new_offset);
        } else if (aarch64_insn_uses_literal(insn)) {
                /*
                 * Disallow patching unhandled instructions using PC relative