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RISC-V Topic Guide

System Call

RISC-V system calls are defined by the execution environment or OS ABI; in common Unix/Linux environments, U-mode ECALL raises an environment-call-from-U-mode exception that may be delegated to S-mode via medeleg, with the syscall number in a7 and up to six arguments typically in a0-a5.

ECALLa7a0-a5sepcmepcscausemcausemedelegSRETenvironment call

Core Concepts

ECALL

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a7

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a0-a5

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sepc

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mepc

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scause

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mcause

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medeleg

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SRET

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environment call

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Related Entries

exception-handlingtrap-handlingprivilege-levelscalling-conventionfunction-callcsr-access

Official References

RISC-V behavior on this topic should be checked against the official specifications; content additions should only use facts verifiable in these documents.

RISC-V Unprivileged ISA ManualRISC-V Privileged Architecture ManualRISC-V Assembly Programmer's ManualRISC-V psABI Specification