Date: Tue, 30 Jan 2024 22:00:15 +0800 From: Lin Lee <leelin2602@gmail.com> To: freebsd-riscv@freebsd.org Subject: A little bit wondering about how a syscall works Message-ID: <8f66f3ed-2a49-4ebc-89eb-66c53e6d22bb@Spark> In-Reply-To: <9204b5c5-63bc-4c29-af19-1f1bb85f74e8@Spark>
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[-- Attachment #1 --] I am wondering about the function ecall_handler(https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L195), which later executing syscallenter, where &td->td_sa Is used. I have no idea where the value of td->td_sa is being set. It is a little bit confusing. Someone asks me to read cpu_fetch_syscall_args(https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L99), and it indeed explains how td->td_sa is being set. But however, I still have no idea how it works. It is called as a function member in elf64_freebsd_sysvec(https://github.com/freebsd/freebsd-src/blob/7aa4e4eb36171d349c7f3948e16c09ff7540c241/sys/riscv/riscv/elf_machdep.c#L61C25-L61C45), and I think there is nothing to do with syscall here. Could somebody please figure it out? How does a system call works? Where the value of td->td_sa is being set. Thank you very much. Best Regards, Lin Lee [-- Attachment #2 --] <html xmlns="http://www.w3.org/1999/xhtml">; <head> <title></title> </head> <body> <div name="messageBodySection"> <div dir="auto">I am wondering about the function ecall_handler(<a href="https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L195" target="_blank">https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L195</a>), which later executing syscallenter, where <span style="color:#000000;font-family:Helvetica Neue;font-size: 13px">&td->td_sa</span><span style="font-size: 13px"><br /></span> Is used. I have no idea where the value of <span style="color:#000000;font-family:Helvetica Neue;font-size: 13px">td->td_sa is </span><span style="color:#000000;font-family:Helvetica Neue;font-size: small">being set. It is a little bit confusing.</span><span style="font-size: small"><br /></span><span style="font-size: small"><br /></span><span style="color:#000000;font-family:Helvetica Neue;font-size: small">Someone asks me to read </span>cpu_fetch_syscall_args(<a href="https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L99" target="_blank">https://github.com/freebsd/freebsd-src/blob/main/sys/riscv/riscv/trap.c#L99</a>), and it indeed explains how <span style="color:#000000;font-family:Helvetica Neue;font-size: small">td->td_sa is being set. But however, I still have no idea how it works.</span><span style="font-size: small"><br /></span><span style="font-size: small"><br /></span><span style="color:#000000;font-family:Helvetica Neue;font-size: small">It is called as a function member in </span>elf64_freebsd_sysvec<span style="color:#000000;font-family:Helvetica Neue;font-size: small">(</span><a href="https://github.com/freebsd/freebsd-src/blob/7aa4e4eb36171d349c7f3948e16c09ff7540c241/sys/riscv/riscv/elf_machdep.c#L61C25-L61C45" target="_blank">https://github.com/freebsd/freebsd-src/blob/7aa4e4eb36171d349c7f3948e16c09ff7540c241/sys/riscv/riscv/elf_machdep.c#L61C25-L61C45</a>), and I think there is nothing to do with syscall here.<br /> <br /> Could somebody please figure it out?<br /> How does a system call works? Where the value of <span style="color:#000000;font-family:Helvetica Neue;font-size: 13px">td->td_sa is </span><span style="color:#000000;font-family:Helvetica Neue;font-size: small">being set.</span><span style="font-size: small"><br /></span><span style="font-size: small"><br /></span><span style="font-size: small"><br /></span><span style="color:#000000;font-family:Helvetica Neue;font-size: small">Thank you very much.</span></div> </div> <div name="messageSignatureSection"><br /> <div class="matchFont">Best Regards, <div dir="auto">Lin Lee</div> </div> </div> </body> </html>home | help
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