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Register Guide

RISC-V t4 / x29 Register: Temporary

Temporary register 4 (x29). The standard psABI marks t4 as not preserved across calls.

ABI name: t4; physical register: x29.
Save rule: Not preserved across calls.
Read it through its psABI role first, then inspect how each instruction reads or writes it.
Related Search Terms
t4 registerx29 registerRISC-V t4t4 temporary registercaller-saved t4t4 not preservedt4 save across calls
Physical Name x29ABI Name t4Save Rule Not preserved across calls
Role
Temporary
Convention
Not preserved across calls
Remember This First
t4 is a standard-psABI temporary register and is not preserved across calls.
psABI Reference

Temporary register

The psABI marks t0-t6 as temporary registers. They are not callee-saved; callers must save any value that needs to survive a call.

Preserved across calls: No
RISC-V psABI integer register convention
Quick Understanding & Search Notes

t4 / x29 belongs to the t0-t6 temporary-register group. The psABI marks it not preserved across calls; callers must save any value that needs to survive a call.

t0-t6 are temporary registers and are not preserved across calls.
If a t4 value is still needed across a call, the caller must save it explicitly.
RISC-V psABI v1.0: Integer register convention

When It Fits Best

  • - Recognize t4 as a temporary register not preserved across calls in the standard psABI.
  • - On procedure exit, contents not specified as return values or callee-saved are unspecified.
  • - The temporary-register classification does not prescribe a particular call sequence or save location.

When Not To Use It This Way

  • - Do not assume a pre-call t4 value remains available after a call.
  • - Do not describe the psABI temporary classification as special hardware behavior.

What Happens Around A Call

1

t4 is a standard-psABI temporary register and is not preserved across calls.

2

Contents not specified as return values or callee-saved are unspecified on procedure exit.

3

This rule applies to the standard calling convention.

Standard psABI Rule For t4

Examples explain the rule, not a complete program
# t4: temporary register, not preserved across calls
# Scope: standard psABI calling convention

FAQ

Is t4 / x29 preserved across calls?

No. t0-t6 are temporary registers and are not preserved across calls.

What if a t4 value is needed after a call?

The caller must save it before the call, usually to the stack or another suitable location, and restore it afterward.