From: Nicholas Piggin <npiggin@gmail.com> To: "Dmitry V. Levin" <ldv@altlinux.org>, Michael Ellerman <mpe@ellerman.id.au> Cc: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>, libc-alpha@sourceware.org, libc-dev@lists.llvm.org, linux-api@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Matheus Castanho <msc@linux.ibm.com>, musl@lists.openwall.com Subject: Re: Linux powerpc new system call instruction and ABI Date: Thu, 20 May 2021 08:51:53 +1000 [thread overview] Message-ID: <1621464056.o9t21cquw8.astroid@bobo.none> (raw) In-Reply-To: <20210519132656.GA17204@altlinux.org> Excerpts from Dmitry V. Levin's message of May 19, 2021 11:26 pm: > On Wed, May 19, 2021 at 08:59:05PM +1000, Nicholas Piggin wrote: >> Excerpts from Dmitry V. Levin's message of May 19, 2021 8:24 pm: >> > On Wed, May 19, 2021 at 12:50:24PM +1000, Nicholas Piggin wrote: >> > [...] >> >> With this patch, I think the ptrace ABI should mostly be fixed. I think >> >> a problem remains with applications that look at system call return >> >> registers directly and have powerpc specific error cases. Those probably >> >> will just need to be updated unfortunately. Michael thought it might be >> >> possible to return an indication via ptrace somehow that the syscall is >> >> using a new ABI, so such apps can be updated to test for it. I don't >> >> know how that would be done. >> > >> > Is there any sane way for these applications to handle the scv case? >> > How can they tell that the scv semantics is being used for the given >> > syscall invocation? Can this information be obtained e.g. from struct >> > pt_regs? >> >> Not that I know of. Michael suggested there might be a way to add >> something. ptrace_syscall_info has some pad bytes, could >> we use one for flags bits and set a bit for "new system call ABI"? > > PTRACE_GET_SYSCALL_INFO is an architecture-agnostic API, it hides all > architecture-specific details behind struct ptrace_syscall_info which has > the same meaning on all architectures. ptrace_syscall_info.exit contains > both rval and is_error fields to support every architecture regardless of > its syscall ABI. > > ptrace_syscall_info.exit is extensible, but every architecture would have > to define a method of telling whether the system call follows the "new > system call ABI" conventions to export this bit of information. It's already architecture speicfic if you look at registers of syscall exit state so I don't see a problem with a flag that ppc can use for ABI. > > This essentially means implementing something like > static inline long syscall_get_error_abi(struct task_struct *task, struct pt_regs *regs) > for every architecture, and using it along with syscall_get_error > in ptrace_get_syscall_info_exit to initialize the new field in > ptrace_syscall_info.exit structure. Yes this could work. Other architectures can just use a generic implementation if they don't define their own so that's easy. And in userspace they can continue to ignore the flag. > >> As a more hacky thing you could make a syscall with -1 and see how >> the error looks, and then assume all syscalls will be the same. > > This would be very unreliable because sc and scv are allowed to intermingle, > so every syscall invocation can follow any of these two error handling > conventions. > >> Or... is it possible at syscall entry to peek the address of >> the instruction which caused the call and see if that was a >> scv instruction? That would be about as reliable as possible >> without having that new flag bit. > > No other architecture requires peeking into tracee memory just to find out > the syscall ABI. This would make powerpc the most ugly architecture for > ptracing. > > I wonder why can't this information be just exported to the tracer via > struct pt_regs? It might be able to, I don't see why that would be superior though. Where could you put it... I guess it could go in the trap field in a high bit. But could that break things that just test for syscall trap number (and don't care about register ABI)? I'm not sure. Thanks, Nick
WARNING: multiple messages have this Message-ID (diff)
From: Nicholas Piggin <npiggin@gmail.com> To: "Dmitry V. Levin" <ldv@altlinux.org>, Michael Ellerman <mpe@ellerman.id.au> Cc: libc-alpha@sourceware.org, Matheus Castanho <msc@linux.ibm.com>, linux-api@vger.kernel.org, musl@lists.openwall.com, libc-dev@lists.llvm.org, linuxppc-dev@lists.ozlabs.org Subject: Re: Linux powerpc new system call instruction and ABI Date: Thu, 20 May 2021 08:51:53 +1000 [thread overview] Message-ID: <1621464056.o9t21cquw8.astroid@bobo.none> (raw) In-Reply-To: <20210519132656.GA17204@altlinux.org> Excerpts from Dmitry V. Levin's message of May 19, 2021 11:26 pm: > On Wed, May 19, 2021 at 08:59:05PM +1000, Nicholas Piggin wrote: >> Excerpts from Dmitry V. Levin's message of May 19, 2021 8:24 pm: >> > On Wed, May 19, 2021 at 12:50:24PM +1000, Nicholas Piggin wrote: >> > [...] >> >> With this patch, I think the ptrace ABI should mostly be fixed. I think >> >> a problem remains with applications that look at system call return >> >> registers directly and have powerpc specific error cases. Those probably >> >> will just need to be updated unfortunately. Michael thought it might be >> >> possible to return an indication via ptrace somehow that the syscall is >> >> using a new ABI, so such apps can be updated to test for it. I don't >> >> know how that would be done. >> > >> > Is there any sane way for these applications to handle the scv case? >> > How can they tell that the scv semantics is being used for the given >> > syscall invocation? Can this information be obtained e.g. from struct >> > pt_regs? >> >> Not that I know of. Michael suggested there might be a way to add >> something. ptrace_syscall_info has some pad bytes, could >> we use one for flags bits and set a bit for "new system call ABI"? > > PTRACE_GET_SYSCALL_INFO is an architecture-agnostic API, it hides all > architecture-specific details behind struct ptrace_syscall_info which has > the same meaning on all architectures. ptrace_syscall_info.exit contains > both rval and is_error fields to support every architecture regardless of > its syscall ABI. > > ptrace_syscall_info.exit is extensible, but every architecture would have > to define a method of telling whether the system call follows the "new > system call ABI" conventions to export this bit of information. It's already architecture speicfic if you look at registers of syscall exit state so I don't see a problem with a flag that ppc can use for ABI. > > This essentially means implementing something like > static inline long syscall_get_error_abi(struct task_struct *task, struct pt_regs *regs) > for every architecture, and using it along with syscall_get_error > in ptrace_get_syscall_info_exit to initialize the new field in > ptrace_syscall_info.exit structure. Yes this could work. Other architectures can just use a generic implementation if they don't define their own so that's easy. And in userspace they can continue to ignore the flag. > >> As a more hacky thing you could make a syscall with -1 and see how >> the error looks, and then assume all syscalls will be the same. > > This would be very unreliable because sc and scv are allowed to intermingle, > so every syscall invocation can follow any of these two error handling > conventions. > >> Or... is it possible at syscall entry to peek the address of >> the instruction which caused the call and see if that was a >> scv instruction? That would be about as reliable as possible >> without having that new flag bit. > > No other architecture requires peeking into tracee memory just to find out > the syscall ABI. This would make powerpc the most ugly architecture for > ptracing. > > I wonder why can't this information be just exported to the tracer via > struct pt_regs? It might be able to, I don't see why that would be superior though. Where could you put it... I guess it could go in the trap field in a high bit. But could that break things that just test for syscall trap number (and don't care about register ABI)? I'm not sure. Thanks, Nick
next prev parent reply other threads:[~2021-05-19 22:52 UTC|newest] Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-11 8:12 Linux powerpc new system call instruction and ABI Nicholas Piggin 2020-06-11 8:12 ` Nicholas Piggin 2020-06-11 8:12 ` [PATCH 1/2] powerpc/64s/exception: treat NIA below __end_interrupts as soft-masked Nicholas Piggin 2020-06-11 8:12 ` Nicholas Piggin 2020-07-24 13:25 ` Michael Ellerman 2020-07-24 13:25 ` Michael Ellerman 2020-06-11 8:12 ` [PATCH 2/2] powerpc/64s: system call support for scv/rfscv instructions Nicholas Piggin 2020-06-11 8:12 ` Nicholas Piggin 2020-07-23 6:47 ` Michael Ellerman 2020-07-23 16:48 ` Christophe Leroy 2020-07-23 16:48 ` Christophe Leroy 2020-07-24 10:45 ` Michael Ellerman 2020-07-24 10:45 ` Michael Ellerman 2020-06-11 21:02 ` Linux powerpc new system call instruction and ABI Segher Boessenkool 2020-06-11 21:02 ` Segher Boessenkool 2020-06-14 9:26 ` Nicholas Piggin 2020-06-14 9:26 ` Nicholas Piggin 2021-05-18 23:13 ` Dmitry V. Levin 2021-05-18 23:13 ` Dmitry V. Levin 2021-05-19 2:50 ` Nicholas Piggin 2021-05-19 2:50 ` Nicholas Piggin 2021-05-19 5:01 ` Nicholas Piggin 2021-05-19 5:01 ` Nicholas Piggin 2021-05-21 19:40 ` Matheus Castanho 2021-05-21 19:40 ` Matheus Castanho 2021-05-21 19:52 ` Florian Weimer 2021-05-21 19:52 ` Florian Weimer 2021-05-21 20:00 ` Matheus Castanho 2021-05-21 20:00 ` Matheus Castanho 2021-05-21 20:52 ` Dmitry V. Levin 2021-05-21 20:52 ` Dmitry V. Levin 2021-05-24 12:11 ` Matheus Castanho 2021-05-24 12:11 ` Matheus Castanho 2021-05-24 20:33 ` Matheus Castanho 2021-05-24 20:33 ` Matheus Castanho 2021-05-19 10:24 ` Dmitry V. Levin 2021-05-19 10:24 ` Dmitry V. Levin 2021-05-19 10:59 ` Nicholas Piggin 2021-05-19 10:59 ` Nicholas Piggin 2021-05-19 12:39 ` Tulio Magno Quites Machado Filho 2021-05-19 12:39 ` Tulio Magno Quites Machado Filho 2021-05-19 13:26 ` Dmitry V. Levin 2021-05-19 13:26 ` Dmitry V. Levin 2021-05-19 22:51 ` Nicholas Piggin [this message] 2021-05-19 22:51 ` Nicholas Piggin 2021-05-19 23:27 ` Dmitry V. Levin 2021-05-19 23:27 ` Dmitry V. Levin 2021-05-20 2:40 ` Nicholas Piggin 2021-05-20 2:40 ` Nicholas Piggin 2021-05-20 3:06 ` Dmitry V. Levin 2021-05-20 3:06 ` Dmitry V. Levin 2021-05-20 5:12 ` Nicholas Piggin 2021-05-20 5:12 ` Nicholas Piggin 2021-05-19 7:33 ` Joakim Tjernlund 2021-05-19 7:33 ` Joakim Tjernlund 2021-05-19 7:55 ` Nicholas Piggin 2021-05-19 7:55 ` Nicholas Piggin 2021-05-19 8:08 ` Joakim Tjernlund 2021-05-19 8:08 ` Joakim Tjernlund 2021-05-19 8:42 ` Nicholas Piggin 2021-05-19 8:42 ` Nicholas Piggin 2021-05-19 11:12 ` Nicholas Piggin 2021-05-19 11:12 ` Nicholas Piggin 2021-05-19 14:38 ` Segher Boessenkool 2021-05-19 14:38 ` Segher Boessenkool 2021-05-19 15:06 ` Joakim Tjernlund 2021-05-19 15:06 ` Joakim Tjernlund 2021-05-19 15:22 ` Segher Boessenkool 2021-05-19 15:22 ` Segher Boessenkool 2021-05-19 15:36 ` [musl] " Rich Felker 2021-05-19 15:36 ` Rich Felker 2021-05-19 18:09 ` Joakim Tjernlund 2021-05-19 18:09 ` Joakim Tjernlund 2021-05-19 23:48 ` [musl] " Rich Felker 2021-05-19 23:48 ` Rich Felker 2021-05-20 1:06 ` Dmitry V. Levin 2021-05-20 1:06 ` Dmitry V. Levin 2021-05-20 2:45 ` Nicholas Piggin 2021-05-20 2:45 ` Nicholas Piggin 2021-05-20 2:59 ` Dmitry V. Levin 2021-05-20 2:59 ` Dmitry V. Levin 2021-05-20 7:20 ` Nicholas Piggin 2021-05-20 7:20 ` Nicholas Piggin
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