[PATCH v2] Reset errno before PTRACE_PEEKUSER for MIPS DSP_CONTROL

[James Hogan <james.hogan@imgtec.com>]

PTRACE_PEEKUSER can return -1, which is usually used to determine whether
a system call has reported an error, so errno must be used alone to
determine whether an error occurred. However errno isn't modified by a
successful system call so it must be reset to a known value (0) before the
syscall call.

Add the missing errno reset when reading the DSP_CONTROL register in the
native MIPS Linux backend and the MIPS gdbserver backend.

gdb/:
	* mips-linux-nat.c (mips_linux_read_description): Reset errno to 0
	prior to reading DSP_CONTROL with PTRACE_PEEKUSER ptrace call.

gdb/gdbserver/:
	* linux-mips-low.c (mips_read_description): Reset errno to 0 prior
	to reading DSP_CONTROL with PTRACE_PEEKUSER ptrace call.
---
Changes in v2:
 - Wrap ChangeLog entries to 74 columns (Maciej W. Rozycki).
---
 gdb/ChangeLog                  | 5 +++++
 gdb/gdbserver/ChangeLog        | 5 +++++
 gdb/gdbserver/linux-mips-low.c | 1 +
 gdb/mips-linux-nat.c           | 1 +
 4 files changed, 12 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 8963878eb8ca..e9e3f9e734e6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2014-09-01  James Hogan  <james.hogan@imgtec.com>
+
+	* mips-linux-nat.c (mips_linux_read_description): Reset errno to 0
+	prior to reading DSP_CONTROL with PTRACE_PEEKUSER ptrace call.
+
 2014-09-01  Maciej W. Rozycki  <macro@codesourcery.com>
 
 	* varobj.c (_initialize_varobj): Move to the end of file.
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index caa243da5d7d..2fa9ec74c08a 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2014-09-01  James Hogan  <james.hogan@imgtec.com>
+
+	* linux-mips-low.c (mips_read_description): Reset errno to 0 prior
+	to reading DSP_CONTROL with PTRACE_PEEKUSER ptrace call.
+
 2014-08-29  Gary Benson  <gbenson@redhat.com>
 
 	* server.h (setjmp.h): Do not include.
diff --git a/gdb/gdbserver/linux-mips-low.c b/gdb/gdbserver/linux-mips-low.c
index 1b2160b35371..377284be5422 100644
--- a/gdb/gdbserver/linux-mips-low.c
+++ b/gdb/gdbserver/linux-mips-low.c
@@ -128,6 +128,7 @@ mips_read_description (void)
     {
       int pid = lwpid_of (current_inferior);
 
+      errno = 0;
       ptrace (PTRACE_PEEKUSER, pid, DSP_CONTROL, 0);
       switch (errno)
 	{
diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c
index 88faa1edf692..ffc8411ca3bc 100644
--- a/gdb/mips-linux-nat.c
+++ b/gdb/mips-linux-nat.c
@@ -439,6 +439,7 @@ mips_linux_read_description (struct target_ops *ops)
       if (tid == 0)
 	tid = ptid_get_pid (inferior_ptid);
 
+      errno = 0;
       ptrace (PTRACE_PEEKUSER, tid, DSP_CONTROL, 0);
       switch (errno)
 	{
-- 
1.8.5.5