Martin Storsjö : ntdll: Zero-initialize the syscall_frame used for starting threads on ARM/ARM64.

[Alexandre Julliard]

Module: wine
Branch: stable
Commit: bb8b9899d485fd1912f93d04b172e6b6e7bffec5
URL:    https://gitlab.winehq.org/wine/wine/-/commit/bb8b9899d485fd1912f93d04b172e6b...

Author: Martin Storsjö 
Date:   Fri Mar  4 18:15:56 2022 +0200

ntdll: Zero-initialize the syscall_frame used for starting threads on ARM/ARM64.

This fixes an inconsistency since
fed7e7a78b4bea183d0cbb107953e275f17baa4f (ntdll: Simulate a syscall
return when starting a thread); in that commit, on i386 and
x86_64, the syscall_frame used for starting the thread was
zeroed with a memset, while it wasn't on arm and arm64.

This had a noticable effect on float maths, where the
uninitialized frame->restore_flags field could have the
CONTEXT_FLOATING_POINT bit set. (call_init_thunk only ORs in
CONTEXT_INTEGER into the restore_flags field, on all architectures).
If that bit was set, it would restore uninitialized data into the
fpscr register, possibly setting the FPU in a nondefault rounding
mode.

Signed-off-by: Martin Storsjö 
Signed-off-by: Alexandre Julliard 
(cherry picked from commit 482b6a6dea4f73db84354ff31c5cde20998aaa81)
Signed-off-by: Michael Stefaniuc

---

dlls/ntdll/unix/signal_arm.c   | 1 +
 dlls/ntdll/unix/signal_arm64.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/dlls/ntdll/unix/signal_arm.c b/dlls/ntdll/unix/signal_arm.c
index a1bcb0ddd32..1fea76f6563 100644
--- a/dlls/ntdll/unix/signal_arm.c
+++ b/dlls/ntdll/unix/signal_arm.c
@@ -1105,6 +1105,7 @@ void DECLSPEC_HIDDEN call_init_thunk( LPTHREAD_START_ROUTINE entry, void *arg, B
     ctx = (CONTEXT *)((ULONG_PTR)context.Sp & ~15) - 1;
     *ctx = context;
     ctx->ContextFlags = CONTEXT_FULL;
+    memset( frame, 0, sizeof(*frame) );
     NtSetContextThread( GetCurrentThread(), ctx );

frame->sp = (DWORD)ctx;
diff --git a/dlls/ntdll/unix/signal_arm64.c b/dlls/ntdll/unix/signal_arm64.c
index 94f280e218a..1df97f16f13 100644
--- a/dlls/ntdll/unix/signal_arm64.c
+++ b/dlls/ntdll/unix/signal_arm64.c
@@ -1202,6 +1202,7 @@ void DECLSPEC_HIDDEN call_init_thunk( LPTHREAD_START_ROUTINE entry, void *arg, B
     ctx = (CONTEXT *)((ULONG_PTR)context.Sp & ~15) - 1;
     *ctx = context;
     ctx->ContextFlags = CONTEXT_FULL;
+    memset( frame, 0, sizeof(*frame) );
     NtSetContextThread( GetCurrentThread(), ctx );

frame->sp    = (ULONG64)ctx;