[PATCH v2 2/2] ntdll: Clear the first ~1MB of stack in signal_start_thread.

[Rémi Bernon]

Instead of the whole stack.

Stack creation in virtual_alloc_thread_stack and RtlCreateUserStack, as
well as Windows rounding logic, enforce a minimum reserved size of 1MB.

There's a few guard and canary pages used on the bottom, plus a few more
on the top for initial context, and we have to keep a bit of space if we
ever need a stack while doing this, so we clear a bit less than 1MB to
be safe.

Signed-off-by: Rémi Bernon <rbernon at codeweavers.com>
---
 dlls/ntdll/signal_i386.c   | 4 ++--
 dlls/ntdll/signal_x86_64.c | 5 ++---
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/dlls/ntdll/signal_i386.c b/dlls/ntdll/signal_i386.c
index 635b8f4de81..7261d398942 100644
--- a/dlls/ntdll/signal_i386.c
+++ b/dlls/ntdll/signal_i386.c
@@ -507,8 +507,8 @@ __ASM_GLOBAL_FUNC( signal_start_thread,
                    "leal -12(%esi),%ecx\n\t"
                    /* clear the thread stack */
                    "andl $~0xfff,%ecx\n\t"   /* round down to page size */
-                   "movl %fs:8,%edi\n\t"     /* NtCurrentTeb()->Tib.StackLimit */
-                   "addl $0x1000,%edi\n\t"
+                   "movl %ecx,%edi\n\t"
+                   "subl $0xf0000,%edi\n\t"
                    "movl %edi,%esp\n\t"
                    "subl %edi,%ecx\n\t"
                    "xorl %eax,%eax\n\t"
diff --git a/dlls/ntdll/signal_x86_64.c b/dlls/ntdll/signal_x86_64.c
index d88f7ae553a..be8d6e22330 100644
--- a/dlls/ntdll/signal_x86_64.c
+++ b/dlls/ntdll/signal_x86_64.c
@@ -1544,9 +1544,8 @@ __ASM_GLOBAL_FUNC( signal_start_thread,
                    "movq %rcx,%rbx\n\t"        /* context */
                    /* clear the thread stack */
                    "andq $~0xfff,%rcx\n\t"     /* round down to page size */
-                   "movq %gs:0x30,%rax\n\t"
-                   "movq 0x10(%rax),%rdi\n\t"  /* NtCurrentTeb()->Tib.StackLimit */
-                   "addq $0x2000,%rdi\n\t"
+                   "movq %rcx,%rdi\n\t"
+                   "subq $0xf0000,%rdi\n\t"
                    "movq %rdi,%rsp\n\t"
                    "subq %rdi,%rcx\n\t"
                    "xorl %eax,%eax\n\t"
-- 
2.30.2