From: Segher Boessenkool <segher@kernel.crashing.org> To: Nicholas Piggin <npiggin@gmail.com> Cc: linuxppc-dev@lists.ozlabs.org, libc-dev@lists.llvm.org, musl@lists.openwall.com, linux-api@vger.kernel.org Subject: Re: Linux powerpc new system call instruction and ABI Date: Thu, 11 Jun 2020 16:02:30 -0500 [thread overview] Message-ID: <20200611210230.GH31009@gate.crashing.org> (raw) In-Reply-To: <20200611081203.995112-1-npiggin@gmail.com> Hi! On Thu, Jun 11, 2020 at 06:12:01PM +1000, Nicholas Piggin wrote: > Calling convention > ------------------ > The proposal is for scv 0 to provide the standard Linux system call ABI > with the following differences from sc convention[1]: > > - lr is to be volatile across scv calls. This is necessary because the > scv instruction clobbers lr. From previous discussion, this should be > possible to deal with in GCC clobbers and CFI. > > - cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow the > kernel system call exit to avoid restoring the volatile cr registers > (although we probably still would anyway to avoid information leaks). > > - Error handling: The consensus among kernel, glibc, and musl is to move to > using negative return values in r3 rather than CR0[SO]=1 to indicate error, > which matches most other architectures, and is closer to a function call. What about cr0 then? Will it be volatile as well (exactly like for function calls)? > Notes > ----- > - r0,r4-r8 are documented as volatile in the ABI, but the kernel patch as > submitted currently preserves them. This is to leave room for deciding > which way to go with these. The kernel has to set it to *something* that doesn't leak information ;-) Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org> To: Nicholas Piggin <npiggin@gmail.com> Cc: libc-dev@lists.llvm.org, linux-api@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, musl@lists.openwall.com Subject: Re: Linux powerpc new system call instruction and ABI Date: Thu, 11 Jun 2020 16:02:30 -0500 [thread overview] Message-ID: <20200611210230.GH31009@gate.crashing.org> (raw) In-Reply-To: <20200611081203.995112-1-npiggin@gmail.com> Hi! On Thu, Jun 11, 2020 at 06:12:01PM +1000, Nicholas Piggin wrote: > Calling convention > ------------------ > The proposal is for scv 0 to provide the standard Linux system call ABI > with the following differences from sc convention[1]: > > - lr is to be volatile across scv calls. This is necessary because the > scv instruction clobbers lr. From previous discussion, this should be > possible to deal with in GCC clobbers and CFI. > > - cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow the > kernel system call exit to avoid restoring the volatile cr registers > (although we probably still would anyway to avoid information leaks). > > - Error handling: The consensus among kernel, glibc, and musl is to move to > using negative return values in r3 rather than CR0[SO]=1 to indicate error, > which matches most other architectures, and is closer to a function call. What about cr0 then? Will it be volatile as well (exactly like for function calls)? > Notes > ----- > - r0,r4-r8 are documented as volatile in the ABI, but the kernel patch as > submitted currently preserves them. This is to leave room for deciding > which way to go with these. The kernel has to set it to *something* that doesn't leak information ;-) Segher
next prev parent reply other threads:[~2020-06-11 21:02 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 ` Segher Boessenkool [this message] 2020-06-11 21:02 ` Linux powerpc new system call instruction and ABI 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 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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