linux-user: Make sigaltstack stacks per-thread

The alternate signal stack set up by the sigaltstack syscall is
supposed to be per-thread.  We were incorrectly implementing it as
process-wide.  This causes problems for guest binaries that rely on
this.  Notably the Go runtime does, and so we were seeing crashes
caused by races where two guest threads might incorrectly both
execute on the same stack simultaneously.

Replace the global target_sigaltstack_used with a field
sigaltstack_used in the TaskState, and make all the references to the
old global instead get a pointer to the TaskState and use the field.

Fixes: https://bugs.launchpad.net/qemu/+bug/1696773
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20190725131645.19501-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 0 insertions, 1 deletions

diff --git a/linux-user/signal-common.h b/linux-user/signal-common.h
index 51030a9306..1df1068552 100644
--- a/linux-user/signal-common.h
+++ b/linux-user/signal-common.h
@@ -19,7 +19,6 @@
 
 #ifndef SIGNAL_COMMON_H
 #define SIGNAL_COMMON_H
-extern struct target_sigaltstack target_sigaltstack_used;
 
 int on_sig_stack(unsigned long sp);
 int sas_ss_flags(unsigned long sp);