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

[Dmitry V. Levin]

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>
---

Notes:
    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)
 {
-- 
ldv