[musl] Re: Linux powerpc new system call instruction and ABI

[Nicholas Piggin <npiggin@gmail.com>]

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 \