All instructionsArm64 · AArch64Control flow

BLR

Call through a register

Save the next instruction address in X30 and branch to the original value of Xn.

Armv8-A

Instruction forms

1 in this sample
FormBitsRequiresEncoding
BLR Xn64Armv8-A1101011000111111000000xxxxx00000
64 bits

Operation

Pseudo-C · selected form
target = Xn
X30 = PC + 4
PC = target

Simplified pseudocode for the selected form.

What to watch for

  • The target is read before X30 is overwritten, including when Xn is X30. SP is not accepted.
  • Target fetches can fault; authentication and guarded-page behavior are outside this simplified operation.

Architectural details

Flags
NZCV unchanged.
Destination
Writes X30 and PC; does not allocate a stack frame.
Encoding
1101011000111111000000xxxxx00000
Operands
  • Xnread · 64 bits
  • X30write · 64 bits
  • PCwrite · 64 bits
Coverage
Selected baseline A64 scalar register forms.
Exception information & execution requirements

    Complete exception conditions have not been imported.

    MRS supplies encoding and availability conditions, not an exhaustive exception model.

    Feature availability alone does not guarantee execution: OS state and execution-level controls also apply. Use the linked architecture documentation for the full exception conditions.

    Performance measurements are not included in this preview. Latency and throughput depend on the exact form and microarchitecture.

    Sources & provenance

    Technical fields are imported from pinned upstream files. Explanations and explorer behavior are maintained separately.

    Architectural references for this form

    These references support the original explanation. Arm MRS supplies encoding patterns (bit 31 first; x means variable) and architectural conditions, but omits execution pseudocode. ACLE supplies intrinsic mappings. Operand restrictions apply separately.

    Arm · aarchmrs
    Revision
    2026-03_rel
    SHA-256
    bf355d263eed08ef6b3e4e680e6bba3642fa7c3dd0be77ffb4783420041a0860
    Terms
    BSD-3-Clause
    View pinned upstream file ↗

    Intel sources are a documentation preview. Arm ACLE mappings are adapted under CC BY-SA 4.0 with an additional patent license. Arm MRS encoding data is distributed under BSD-3-Clause. © Arm Limited and contributors. Coverage and attribution.