Why is s2 / x18 suitable for values that survive calls?
s0-s11 are preserved across calls; a callee that modifies them must restore them, so callers can rely on their values after return.
Register Guide
RISC-V s2 / x18 Register: Saved register
Saved register 2 in the standard psABI; a function that modifies it must restore its entry value before returning.
ABI name: s2; physical register: x18.
Save rule: Callee, if modified.
Read it through its psABI role first, then inspect how each instruction reads or writes it.
Physical Name x18ABI Name s2Save Rule Callee, if modified
Role
Saved register
Convention
Standard psABI: preserved across calls
Remember This First
The standard psABI marks s0-s11 as preserved across calls.
psABI Reference
Saved register
The psABI marks s0-s11 as preserved across calls. A callee that modifies them must restore their entry values before returning. s2 has no frame-pointer alias; the optional frame-pointer rule applies only to x8/s0.
Preserved across calls: Yes
RISC-V psABI integer register conventionQuick Understanding & Search Notes
s2 / x18 belongs to the s0-s11 saved-register group. The psABI marks it preserved across calls; a callee that modifies it must restore it before returning.
s0-s11 are saved registers preserved across calls.
A callee that modifies s2 must restore its original value before returning.
When It Fits Best
- - Recognize it as a register preserved across calls in the standard psABI.
- - Restore its entry value before returning when a procedure modifies it.
- - s2 is a saved register; the frame-pointer alias belongs only to x8/s0.
When Not To Use It This Way
- - Do not modify s* and return without restoring it.
- - Do not describe s2 as a frame pointer; that optional role belongs only to x8/s0.
What Happens Around A Call
1
The standard psABI marks s0-s11 as preserved across calls.
2
A callee that modifies s* must restore its entry value before returning.
3
s2 has no frame-pointer alias.
Standard psABI Preservation Rule
Examples explain the rule, not a complete program# s2 is a register preserved across calls
# A procedure that modifies s2 must restore its entry value before returningFAQ
Who restores s2 if a function modifies it?
The callee restores it before returning.