linux-user: Support for restarting system calls for Microblaze targets

Update the Microblaze main loop and sigreturn code:
 * on TARGET_ERESTARTSYS, wind guest PC backwards to repeat syscall insn
 * set all guest CPU state within signal.c code on sigreturn
 * handle TARGET_QEMU_ESIGRETURN in the main loop as the indication
   that the main loop should not touch any guest CPU state

Note that this in passing fixes a bug where we were corrupting
the guest r[3] on sigreturn with the guest's r[10] because
do_sigreturn() was returning env->regs[10] but the register for
syscall return values is env->regs[3].

Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-11-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: Commit message tweaks; drop TARGET_USE_ERESTARTSYS define;
 drop whitespace changes]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/linux-user/main.c b/linux-user/main.c
index c5da418fa4..b2bc6ab2f7 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -2982,7 +2982,12 @@ void cpu_loop(CPUMBState *env)
                              env->regs[9], 
                              env->regs[10],
                              0, 0);
-            env->regs[3] = ret;
+            if (ret == -TARGET_ERESTARTSYS) {
+                /* Wind back to before the syscall. */
+                env->sregs[SR_PC] -= 4;
+            } else if (ret != -TARGET_QEMU_ESIGRETURN) {
+                env->regs[3] = ret;
+            }
             /* All syscall exits result in guest r14 being equal to the
              * PC we return to, because the kernel syscall exit "rtbd" does
              * this. (This is true even for sigreturn(); note that r14 is