Excerpts from Dmitry V. Levin's message of May 19, 2021 9:13 am:
- 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; \
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.