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

This fixes an inconsistency since fed7e7a7 (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 <martin@martin.st> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

ntdll: Zero-initialize the syscall_frame used for starting threads on ARM/ARM64.
482b6a6d · Martin Storsjö · Alexandre Julliard · 9b9d8182 · 482b6a6d · 482b6a6d
Commit 482b6a6d authored Mar 04, 2022 by Martin Storsjö Committed by Alexandre Julliard Mar 04, 2022
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signal_arm.c dlls/ntdll/unix/signal_arm.c +1 -0

signal_arm64.c dlls/ntdll/unix/signal_arm64.c +1 -0

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--- 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;

--- 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;