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Message-Id: <1621400263.gf0mbqhkrf.astroid@bobo.none>
Date: Wed, 19 May 2021 15:01:12 +1000
From: Nicholas Piggin <npiggin@...il.com>
To: "Dmitry V. Levin" <ldv@...linux.org>, Michael Ellerman
<mpe@...erman.id.au>
Cc: libc-alpha@...rceware.org, libc-dev@...ts.llvm.org,
linux-api@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, Matheus Castanho
<msc@...ux.ibm.com>, musl@...ts.openwall.com
Subject: Re: Linux powerpc new system call instruction and ABI
Excerpts from Nicholas Piggin's message of May 19, 2021 12:50 pm:
> Excerpts from Dmitry V. Levin's message of May 19, 2021 9:13 am:
>> Hi,
>>
>> On Thu, Jun 11, 2020 at 06:12:01PM +1000, Nicholas Piggin wrote:
>> [...]
>>> - 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.
>>
>> Apparently, the patchset merged by commit v5.9-rc1~100^2~164 was
>> incomplete: all functions defined in arch/powerpc/include/asm/ptrace.h and
>> arch/powerpc/include/asm/syscall.h that use ccr are broken when scv is used.
>> This includes syscall_get_error() and all its users including
>> PTRACE_GET_SYSCALL_INFO API, which in turn makes strace unusable
>> when scv is used.
>>
>> See also https://bugzilla.redhat.com/1929836
>
> I see, thanks. Using latest strace from github.com, the attached kernel
> patch makes strace -k check results a lot greener.
>
> Some of the remaining failing tests look like this (I didn't look at all
> of them yet):
>
> signal(SIGUSR1, 0xfacefeeddeadbeef) = 0 (SIG_DFL)
> write(1, "signal(SIGUSR1, 0xfacefeeddeadbe"..., 50signal(SIGUSR1, 0xfacefeeddeadbeef) = 0 (SIG_DFL)
> ) = 50
> signal(SIGUSR1, SIG_IGN) = 0xfacefeeddeadbeef
> write(2, "errno2name.c:461: unknown errno "..., 41errno2name.c:461: unknown errno 559038737) = 41
> write(2, ": Unknown error 559038737\n", 26: Unknown error 559038737
> ) = 26
> exit_group(1) = ?
>
> I think the problem is glibc testing for -ve, but it should be comparing
> against -4095 (+cc Matheus)
>
> #define RET_SCV \
> cmpdi r3,0; \
> bgelr+; \
> neg r3,r3;
This glibc patch at least gets that signal test working. Haven't run the
full suite yet because of trouble making it work with a local glibc
install...
Thanks,
Nick
---
diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
index c57bb1c05d..1ea4c3b917 100644
--- a/sysdeps/powerpc/powerpc64/sysdep.h
+++ b/sysdeps/powerpc/powerpc64/sysdep.h
@@ -398,8 +398,9 @@ LT_LABELSUFFIX(name,_name_end): ; \
#endif
#define RET_SCV \
- cmpdi r3,0; \
- bgelr+; \
+ li r9,-4095; \
+ cmpld r3,r9; \
+ bltlr+; \
neg r3,r3;
#define RET_SC \
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