The BLX instruction is encoded differently than the BL, because why not? In
particular, the immediate has 20-bits of value instead of 21. And bit 0 is '0'
always. Going through the BL fixup encoding was trashing the "bit 0 is '0'"
invariant.
Attempt to get the encoding at slightly more correct with this.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121336 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMAsmBackend.cpp b/lib/Target/ARM/ARMAsmBackend.cpp
index 00cd4e7..8e809f0 100644
--- a/lib/Target/ARM/ARMAsmBackend.cpp
+++ b/lib/Target/ARM/ARMAsmBackend.cpp
@@ -146,13 +146,33 @@
// The value doesn't encode the low bit (always zero) and is offset by
// four. The value is encoded into disjoint bit positions in the destination
// opcode. x = unchanged, I = immediate value bit, S = sign extension bit
- // xxxxxSIIIIIIIIII xxxxxIIIIIIIIIII
+ //
+ // BL: xxxxxSIIIIIIIIII xxxxxIIIIIIIIIII
+ //
// Note that the halfwords are stored high first, low second; so we need
// to transpose the fixup value here to map properly.
- // FIXME: Something isn't quite right with this. Some, but not all, BLX
- // instructions are getting the encoded value off by one.
+ unsigned isNeg = (int64_t(Value) < 0) ? 1 : 0;
uint32_t Binary = 0x3fffff & ((Value - 4) >> 1);
- Binary = ((Binary & 0x7ff) << 16) | (Binary >> 11);
+ Binary = (Binary & 0x7ff) << 16; // Low imm11 value.
+ Binary |= (Binary & 0x1ffc00) >> 11; // High imm10 value.
+ Binary |= isNeg << 10; // Sign bit.
+ return Binary;
+ }
+ case ARM::fixup_arm_thumb_blx: {
+ // The value doesn't encode the low two bits (always zero) and is offset by
+ // four (see fixup_arm_thumb_cp). The value is encoded into disjoint bit
+ // positions in the destination opcode. x = unchanged, I = immediate value
+ // bit, S = sign extension bit, 0 = zero.
+ //
+ // BLX: xxxxxSIIIIIIIIII xxxxxIIIIIIIIII0
+ //
+ // Note that the halfwords are stored high first, low second; so we need
+ // to transpose the fixup value here to map properly.
+ unsigned isNeg = (int64_t(Value) < 0) ? 1 : 0;
+ uint32_t Binary = 0xfffff & ((Value - 2) >> 2);
+ Binary = (Binary & 0x3ff) << 17; // Low imm10L value.
+ Binary |= (Binary & 0xffc00) >> 10; // High imm10H value.
+ Binary |= isNeg << 10; // Sign bit.
return Binary;
}
case ARM::fixup_arm_thumb_cp:
@@ -291,6 +311,7 @@
case ARM::fixup_t2_branch:
case ARM::fixup_t2_pcrel_10:
case ARM::fixup_arm_thumb_bl:
+ case ARM::fixup_arm_thumb_blx:
return 4;
}
}