How is C.EBREAK related to EBREAK?
C.EBREAK performs the same environment-break semantics as EBREAK, encoded as a 16-bit compressed form.
C.EBREAK
RISC-V C.EBREAK Instruction Details
Instruction ManualCCompressed breakpoint instruction that performs the same environment-break operation as EBREAK.
Instruction Syntax
c.ebreak
Operand Breakdown
C.EBREAK has no explicit operands and does not read or write GPRs.
The CR rd/rs1 and rs2 fields are fixed zero; there is no immediate.
CCompressed Instruction
Instruction Behavior
C.EBREAK is the 16-bit CR-format breakpoint instruction in the C extension and performs the same operation as EBREAK. Unless an external debug environment overrides it, it raises a synchronous Breakpoint exception and performs no other operation. It has no operands and does not read or write GPRs.
C.EBREAK Decode And Trap Animation
Restore fixed compressed fields, calculate the exception address, then commit receiving-mode EPC/cause.
no explicit operands
c.ebreakc.ebreak
Execution Context
0x9002 (C.EBREAK) -> Breakpoint
PC=0x0000000000002000 -> EPC=0x0000000000002000; unless an external debug environment overrides it, this raises a synchronous Breakpoint exception.
15..12
11..2
1..0
1001
funct4
0000000000
fixed zero
10
C2
instruction
0x9002 (16-bit)
opcode
10 -> C2 quadrant
CR fixed bits
funct4=1001; bits 11..2=0
fixed
CR format: rd/rs1=0 and rs2=0
context
mode=M, pc=0x0000000000002000
exception
PC=0x0000000000002000 -> EPC=0x0000000000002000; Breakpoint (code 3)
state
EPC/cause not recorded
next EPC
example only: PC + 2 = 0x0000000000002000 + 2 = 0x0000000000002002
Assumes successful fetch, IALIGN=16 (16-bit instruction alignment), no H-extension virtualization, and no external-debug override of EBREAK. Only receiving-mode EPC/cause are illustrated; delegation, trap target address, and handler policy are outside this example.
This animation shows only ISA-visible synchronous exception and state recording; syscall ABI, debugger action, trap-handler policy, and timing are execution-environment or privileged-architecture matters.
Quick Understanding & Search Notes
C.EBREAK is the compressed encoding form of EBREAK for breakpoint/debug entry; it is not an ignorable hint.
C.EBREAK uses the 16-bit CR format: funct4=1001, bits[11:2]=0, and bits[1:0]=10; the shared CR rd/rs1 and rs2 fields are both x0.
It performs the same operation as EBREAK: unless an external debug environment overrides it, it raises a synchronous Breakpoint exception and performs no other operation.
The receiving privilege mode EPC records the C.EBREAK address itself; this synchronous exception does not retire and should not increment minstret.
Common Usage Scenarios
Debug & Monitoring
Understand this scenario with real code like «c.ebreak # Breakpoint unless overridden by external debug».
System & Privilege
Understand this scenario with real code like «c.ebreak # Breakpoint unless overridden by external debug».
Pre-Use Checklist
Syntax Check
- Confirm C or Zca support for the 16-bit C.EBREAK encoding.
- Confirm C.EBREAK has no explicit operands and its shared CR rd/rs1 and rs2 fields are both x0.
Semantic Check
- Unless overridden by an external debug environment, this instruction raises a synchronous Breakpoint exception and performs no ordinary register operation.
- Confirm the receiving privilege mode EPC records this instruction's own address.
Pitfalls / Common Confusions
C.EBREAK is not an ordinary NOP; executing it causes breakpoint/debug-related control transfer.
It has no rd/rs operands; do not interpret it using C.ADD register semantics.
Unless an external debug environment overrides it, C.EBREAK raises a synchronous Breakpoint exception; the receiving privilege mode EPC records this instruction's address, not the following address.
FAQ
Can C.EBREAK be used as NOP?
No. It is a breakpoint instruction.