Date: Fri, 2 Feb 2024 13:49:16 +0800 From: Lin Lee <leelin2602@gmail.com> To: freebsd-riscv@freebsd.org, Mitchell Horne <mhorne@freebsd.org> Subject: Re: A little bit wondering about how a syscall works Message-ID: <bd2bd011-be87-4f87-825b-dd533198bcc9@Spark> In-Reply-To: <51285fdf-dbcf-4d71-82cb-f49353db95cd@freebsd.org> References: <9204b5c5-63bc-4c29-af19-1f1bb85f74e8@Spark> <8f66f3ed-2a49-4ebc-89eb-66c53e6d22bb@Spark> <9bfbdbe2-ff30-4c2f-abf3-2763aa433107@freebsd.org> <f2213278-0807-4a36-ab90-6d2a9555fc8c@Spark> <b4e54e75-fcfd-475c-b0f7-6be7a6cf5e84@freebsd.org> <8867a483-7e92-4579-9236-32b4a704713e@Spark> <51285fdf-dbcf-4d71-82cb-f49353db95cd@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
--65bc826a_5236e554_c55 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Hi, But what I see in=C2=A0https://github.com/freebsd/freebsd-src/blob/main/s= ys/kern/subr=5Fsyscall.c=C2=A0is(after removing some condition branching)= : 77 error =3D (p->p=5Fsysent->sv=5Ffetch=5Fsyscall=5Fargs)(td); 78 se =3D sa->callp; 156=C2=A0=C2=A0error =3D (se->sy=5Fcall)(td, sa->args); It seems that =60sv=5Fset=5Fsyscall=5Fretval hook=60 is called earlier th= an syscall is executed. Thank you so much for your replying. Best Regards, Lin Lee On =46eb 2, 2024 at 12:19 AM +0800, Mitchell Horne <mhorne=40freebsd.org>= , wrote: > On 2/1/24 00:47, Lin Lee wrote: > > Hi, > > > > So, if I understand correctly, > > > > Each thread's sv=5Ffetch=5Fsyscall=5Fargs hook function is initialize= d as > > cpu=5Ffetch=5Fsyscall=5Fargs(), > > > > And when it enter syscallenter, it first use =60error =3D > > (p->p=5Fsysent->sv=5Ffetch=5Fsyscall=5Fargs)(td);=60 to read the syst= em call > > number, then use =60error =3D (se->sy=5Fcall)(td, sa->args)=60 to exe= cute the > > system call. > > > > Do I understand corrected=3F > > > > That's right. > > > Thank you very much. > > > > Best Regards, > > Lin Lee > > On =46eb 1, 2024 at 12:27 AM +0800, Mitchell Horne <mhorne=40freebsd.= org>, > > wrote: > > > On 1/31/24 01:03, Lin Lee wrote: > > > > Hello Mitchell, > > > > > > > > Thank you for your kindly responding. > > > > > > > > Now I have still a question, when does the function > > > > cpu=5Ffetch=5Fsyscall=5Fargs be called=3F > > > > > > > > As the previous letter mentions, I traced the code and entered th= e > > > > elf=5Fmachdep.c. > > > > > > > > I have no idea if there are something to do between elf=5Fmachdep= .c and > > > > system calll. > > > > > > > > > > The short answer is yes, it is related. In syscallenter() we have: > > > > > > error =3D (p->p=5Fsysent->sv=5Ffetch=5Fsyscall=5Fargs)(td); > > > > > > And as you saw, the sv=5Ffetch=5Fsyscall=5Fargs hook is set to > > > cpu=5Ffetch=5Fsyscall=5Fargs() for elf64=5Ffreebsd=5Fsysvec. Simila= rly, there is > > > an sv=5Fset=5Fsyscall=5Fretval hook, called by syscallret() when we= are done > > > executing the system call. > > > > > One correction: the sv=5Fset=5Fsyscall=5Fretval hook is actually called= at the > very end of syscallenter(), after the execution of the syscall has > completed. > > > > Each process 'p' has a corresponding sysentvec (p=5Fsysent). On the= > > > riscv architecture there is currently only one registered systentve= c, > > > elf64=5Ffreebsd=5Fsysvec, because we can only execute 64-bit =46ree= BSD EL=46 > > > binaries on this platform. > > > > > > By contrast, on amd64 there are several registered sysentvecs. This= > > > allows it to execute, for example, 32-bit =46reeBSD EL=46 binaries,= or > > > 64-bit Linux EL=46 binaries. The sysentvec enables different handli= ng > > > for these different types of executables, e.g. the system call tabl= e > > > is different for Linux processes (.sv=5Ftable =3D linux=5Fsysent). > > > > > > You will see also that Linux processes have a different function fo= r > > > sv=5Ffetch=5Fsyscall=5Fargs, take a look in sys/amd64/linux/linux=5F= sysvec.c. > > > > > > Mitchell > > > > > > > If not, when(how) the cpu=5Ffetch=5Fsyscall=5Fargs is called=3F > > > > > > > > Thank you very much. > > > > > > > > Best Regards, > > > > Lin Lee > > > > On Jan 31, 2024 at 1:17 AM +0800, Mitchell Horne <mhorne=40freebs= d.org>, > > > > wrote: > > > > > > > > > > Mitchell > > > > --65bc826a_5236e554_c55 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline <html xmlns=3D=22http://www.w3.org/1999/xhtml=22>; <head> <title></title> </head> <body> <div name=3D=22messageBodySection=22> <div dir=3D=22auto=22>Hi,<br /> <br /> But what I see in&=23160;<a href=3D=22https://github.com/freebsd/freebsd-= src/blob/main/sys/kern/subr=5Fsyscall.c=22 target=3D=22=5Fblank=22>https:= //github.com/freebsd/freebsd-src/blob/main/sys/kern/subr=5Fsyscall.c</a>&= =23160;is(after removing some condition branching):<br /> <br /> <span style=3D=22white-space:pre=22>77 error =3D (p->p=5Fsysent->s= v=5Ffetch=5Fsyscall=5Fargs)(td);</span><br /> <span style=3D=22white-space:pre=22>78 se =3D sa->callp;</span><br /> 156&=23160;&=23160;error =3D (se->sy=5Fcall)(td, sa->args);<br /> <br /> It seems that =60sv=5Fset=5Fsyscall=5Fretval hook=60 is called earlier th= an syscall is executed.<br /> <br /> Thank you so much for your replying.&=23160;</div> </div> <div name=3D=22messageSignatureSection=22><br /> <div class=3D=22match=46ont=22>Best Regards, <div dir=3D=22auto=22>Lin Lee</div> </div> </div> <div name=3D=22messageReplySection=22>On =46eb 2, 2024 at 12:19 AM +0800,= Mitchell Horne <mhorne=40freebsd.org>, wrote:<br /> <blockquote type=3D=22cite=22 style=3D=22border-left-color: grey; border-= left-width: thin; border-left-style: solid; margin: 5px 5px;padding-left:= 10px;=22>On 2/1/24 00:47, Lin Lee wrote:<br /> <blockquote type=3D=22cite=22>Hi,<br /> <br /> So, if I understand correctly,<br /> <br /> Each thread's sv=5Ffetch=5Fsyscall=5Fargs hook function is initialized as= <br /> cpu=5Ffetch=5Fsyscall=5Fargs(),<br /> <br /> And when it enter syscallenter, it first use =60error =3D<br /> (p->p=5Fsysent->sv=5Ffetch=5Fsyscall=5Fargs)(td);=60 to read the sy= stem call<br /> number, then use =60error =3D (se->sy=5Fcall)(td, sa->args)=60 to e= xecute the<br /> system call.<br /> <br /> Do I understand corrected=3F<br /> <br /></blockquote> <br /> That's right.<br /> <br /> <blockquote type=3D=22cite=22>Thank you very much.<br /> <br /> Best Regards,<br /> Lin Lee<br /> On =46eb 1, 2024 at 12:27 AM +0800, Mitchell Horne <mhorne=40freebsd.o= rg>,<br /> wrote:<br /> <blockquote type=3D=22cite=22>On 1/31/24 01:03, Lin Lee wrote:<br /> <blockquote type=3D=22cite=22>Hello Mitchell,<br /> <br /> Thank you for your kindly responding.<br /> <br /> Now I have still a question, when does the function<br /> cpu=5Ffetch=5Fsyscall=5Fargs be called=3F<br /> <br /> As the previous letter mentions, I traced the code and entered the<br /> elf=5Fmachdep.c.<br /> <br /> I have no idea if there are something to do between elf=5Fmachdep.c and<b= r /> system calll.<br /> <br /></blockquote> <br /> The short answer is yes, it is related. In syscallenter() we have:<br /> <br /> error =3D (p->p=5Fsysent->sv=5Ffetch=5Fsyscall=5Fargs)(td);<br /> <br /> And as you saw, the sv=5Ffetch=5Fsyscall=5Fargs hook is set to<br /> cpu=5Ffetch=5Fsyscall=5Fargs() for elf64=5Ffreebsd=5Fsysvec. Similarly, t= here is<br /> an sv=5Fset=5Fsyscall=5Fretval hook, called by syscallret() when we are d= one<br /> executing the system call.<br /> <br /></blockquote> </blockquote> <br /> One correction: the sv=5Fset=5Fsyscall=5Fretval hook is actually called a= t the<br /> very end of syscallenter(), after the execution of the syscall has<br /> completed.<br /> <br /> <blockquote type=3D=22cite=22> <blockquote type=3D=22cite=22>Each process 'p' has a corresponding sysent= vec (p=5Fsysent). On the<br /> riscv architecture there is currently only one registered systentvec,<br = /> elf64=5Ffreebsd=5Fsysvec, because we can only execute 64-bit =46reeBSD EL= =46<br /> binaries on this platform.<br /> <br /> By contrast, on amd64 there are several registered sysentvecs. This<br />= allows it to execute, for example, 32-bit =46reeBSD EL=46 binaries, or<br= /> 64-bit Linux EL=46 binaries. The sysentvec enables different handling<br = /> for these different types of executables, e.g. the system call table<br /= > is different for Linux processes (.sv=5Ftable =3D linux=5Fsysent).<br /> <br /> You will see also that Linux processes have a different function for<br /= > sv=5Ffetch=5Fsyscall=5Fargs, take a look in sys/amd64/linux/linux=5Fsysve= c.c.<br /> <br /> Mitchell<br /> <br /> <blockquote type=3D=22cite=22>If not, when(how) the cpu=5Ffetch=5Fsyscall= =5Fargs is called=3F<br /> <br /> Thank you very much.<br /> <br /> Best Regards,<br /> Lin Lee<br /> On Jan 31, 2024 at 1:17 AM +0800, Mitchell Horne <mhorne=40freebsd.org= >,<br /> wrote:<br /> <blockquote type=3D=22cite=22><br /> Mitchell<br /></blockquote> </blockquote> <br /></blockquote> </blockquote> <br /></blockquote> </div> </body> </html> --65bc826a_5236e554_c55--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bd2bd011-be87-4f87-825b-dd533198bcc9>