Why is s11 / x27 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 s11 / x27 Register: Saved register
Saved register 11 (x27). Under the standard psABI, a procedure that modifies it restores its entry value before returning.
ABI name: s11; physical register: x27.
Save rule: Preserved across calls.
Read it through its psABI role first, then inspect how each instruction reads or writes it.
Physical Name x27ABI Name s11Save Rule Preserved across calls
Role
Saved register
Convention
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. s11 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
s11 / x27 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 s11 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.
- - s11 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 s11 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
s11 has no frame-pointer alias.
Standard psABI Preservation Rule
Examples explain the rule, not a complete program# s11 is a register preserved across calls
# A procedure that modifies s11 must restore its entry value before returningFAQ
Who restores s11 if a function modifies it?
The callee restores it before returning.