[PATCH v11 5/7] powerpc: define syscall_get_error()

From: Dmitry V. Levin
Date: Fri May 10 2019 - 11:29:47 EST

syscall_get_error() is required to be implemented on this
architecture in addition to already implemented syscall_get_nr(),
syscall_get_arguments(), syscall_get_return_value(), and
syscall_get_arch() functions in order to extend the generic
ptrace API with PTRACE_GET_SYSCALL_INFO request.

Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Elvira Khabirova <lineprinter@xxxxxxxxxxxx>
Cc: Eugene Syromyatnikov <esyr@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Signed-off-by: Dmitry V. Levin <ldv@xxxxxxxxxxxx>

v11: added Acked-by from https://lore.kernel.org/lkml/87woj3wwmf.fsf@xxxxxxxxxxxxxxxxxxxxxxxx/
v10: unchanged
v9: unchanged
v8: unchanged
v7: unchanged
v6: unchanged
v5: initial revision

This change has been tested with
tools/testing/selftests/ptrace/get_syscall_info.c and strace,
so it's correct from PTRACE_GET_SYSCALL_INFO point of view.

This cast doubts on commit v4.3-rc1~86^2~81 that changed
syscall_set_return_value() in a way that doesn't quite match
syscall_get_error(), but syscall_set_return_value() is out
of scope of this series, so I'll just let you know my concerns.

See also https://lore.kernel.org/lkml/874lbbt3k6.fsf@xxxxxxxxxxxxxxxxxxxxxxxx/
and https://lore.kernel.org/lkml/87woj3wwmf.fsf@xxxxxxxxxxxxxxxxxxxxxxxx/
for more details on powerpc syscall_set_return_value() confusion.

arch/powerpc/include/asm/syscall.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index a048fed0722f..bd9663137d57 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -38,6 +38,16 @@ static inline void syscall_rollback(struct task_struct *task,
regs->gpr[3] = regs->orig_gpr3;

+static inline long syscall_get_error(struct task_struct *task,
+ struct pt_regs *regs)
+ /*
+ * If the system call failed,
+ * regs->gpr[3] contains a positive ERRORCODE.
+ */
+ return (regs->ccr & 0x10000000UL) ? -regs->gpr[3] : 0;
static inline long syscall_get_return_value(struct task_struct *task,
struct pt_regs *regs)