Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On Fri, Jun 22, 2018 at 8:06 AM wrote: > > On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski wrote: > >On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel > > wrote: > >> > >> From: "H. Peter Anvin" > >> > >> Provide ptrace/regset access to the LDT, if one exists. This > >> interface provides both read and write access. The write code is > >> unified with modify_ldt(); the read code doesn't have enough > >> similarity so it has been kept made separate. > > > >For this and for the GDT, you've chosen to use struct user_desc as > >your format instead of using a native hardware descriptor format. Any > >particular reason why? If nothing else, it will bloat core files a > >bit more than needed. > > I did because REGSET_TLS was implemented that way, and that is simply a > subset of the GDT (which made the same code trivially applicable to both.) > modify_ldt() does it *both* ways for extra fun (one for reading, and one for > writing.) > > ->active is defined as "beyond this point the regset contains only the > default value", which seemed appropriate in this case. I saw that definition too. But I'm still very unclear as to what, if anything, the code actually does :) --Andy
Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On Fri, Jun 22, 2018 at 8:06 AM wrote: > > On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski wrote: > >On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel > > wrote: > >> > >> From: "H. Peter Anvin" > >> > >> Provide ptrace/regset access to the LDT, if one exists. This > >> interface provides both read and write access. The write code is > >> unified with modify_ldt(); the read code doesn't have enough > >> similarity so it has been kept made separate. > > > >For this and for the GDT, you've chosen to use struct user_desc as > >your format instead of using a native hardware descriptor format. Any > >particular reason why? If nothing else, it will bloat core files a > >bit more than needed. > > I did because REGSET_TLS was implemented that way, and that is simply a > subset of the GDT (which made the same code trivially applicable to both.) > modify_ldt() does it *both* ways for extra fun (one for reading, and one for > writing.) > > ->active is defined as "beyond this point the regset contains only the > default value", which seemed appropriate in this case. I saw that definition too. But I'm still very unclear as to what, if anything, the code actually does :) --Andy
Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski wrote: >On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel > wrote: >> >> From: "H. Peter Anvin" >> >> Provide ptrace/regset access to the LDT, if one exists. This >> interface provides both read and write access. The write code is >> unified with modify_ldt(); the read code doesn't have enough >> similarity so it has been kept made separate. > >For this and for the GDT, you've chosen to use struct user_desc as >your format instead of using a native hardware descriptor format. Any >particular reason why? If nothing else, it will bloat core files a >bit more than needed. I did because REGSET_TLS was implemented that way, and that is simply a subset of the GDT (which made the same code trivially applicable to both.) modify_ldt() does it *both* ways for extra fun (one for reading, and one for writing.) ->active is defined as "beyond this point the regset contains only the default value", which seemed appropriate in this case. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On June 22, 2018 7:49:13 AM PDT, Andy Lutomirski wrote: >On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel > wrote: >> >> From: "H. Peter Anvin" >> >> Provide ptrace/regset access to the LDT, if one exists. This >> interface provides both read and write access. The write code is >> unified with modify_ldt(); the read code doesn't have enough >> similarity so it has been kept made separate. > >For this and for the GDT, you've chosen to use struct user_desc as >your format instead of using a native hardware descriptor format. Any >particular reason why? If nothing else, it will bloat core files a >bit more than needed. I did because REGSET_TLS was implemented that way, and that is simply a subset of the GDT (which made the same code trivially applicable to both.) modify_ldt() does it *both* ways for extra fun (one for reading, and one for writing.) ->active is defined as "beyond this point the regset contains only the default value", which seemed appropriate in this case. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel wrote: > > From: "H. Peter Anvin" > > Provide ptrace/regset access to the LDT, if one exists. This > interface provides both read and write access. The write code is > unified with modify_ldt(); the read code doesn't have enough > similarity so it has been kept made separate. For this and for the GDT, you've chosen to use struct user_desc as your format instead of using a native hardware descriptor format. Any particular reason why? If nothing else, it will bloat core files a bit more than needed.
Re: [PATCH v3 7/7] x86/ldt,ptrace: provide regset access to the LDT
On Thu, Jun 21, 2018 at 2:18 PM H. Peter Anvin, Intel wrote: > > From: "H. Peter Anvin" > > Provide ptrace/regset access to the LDT, if one exists. This > interface provides both read and write access. The write code is > unified with modify_ldt(); the read code doesn't have enough > similarity so it has been kept made separate. For this and for the GDT, you've chosen to use struct user_desc as your format instead of using a native hardware descriptor format. Any particular reason why? If nothing else, it will bloat core files a bit more than needed.
