ntdll: Clear the first ~1MB of stack in signal_start_thread.

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@codeweavers.com> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

ntdll: Clear the first ~1MB of stack in signal_start_thread.
96f5968a · Rémi Bernon · Alexandre Julliard · 94dcca8a · 96f5968a · 96f5968a
Commit 96f5968a authored Mar 31, 2021 by Rémi Bernon Committed by Alexandre Julliard Apr 21, 2021
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Showing with 5 additions and 8 deletions

signal_i386.c dlls/ntdll/signal_i386.c +4 -5

signal_x86_64.c dlls/ntdll/signal_x86_64.c +1 -3

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--- a/dlls/ntdll/signal_i386.c
+++ b/dlls/ntdll/signal_i386.c
@@ -504,13 +504,12 @@ USHORT WINAPI RtlCaptureStackBackTrace( ULONG skip, ULONG count, PVOID *buffer, 
 */
 __ASM_GLOBAL_FUNC( signal_start_thread,
                   "movl 4(%esp),%esi\n\t"   /* context */
-                   "leal -12(%esi),%ecx\n\t"
+                   "leal -12(%esi),%edi\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"
+                   "andl $~0xfff,%edi\n\t"   /* round down to page size */
+                   "movl $0xf0000,%ecx\n\t"
+                   "subl %ecx,%edi\n\t"
                   "movl %edi,%esp\n\t"
-                   "subl %edi,%ecx\n\t"
                   "xorl %eax,%eax\n\t"
                   "shrl $2,%ecx\n\t"
                   "rep; stosl\n\t"

--- a/dlls/ntdll/signal_x86_64.c
+++ b/dlls/ntdll/signal_x86_64.c
@@ -1544,9 +1544,7 @@ __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"
+                   "leaq -0xf0000(%rcx),%rdi\n\t"
                   "movq %rdi,%rsp\n\t"
                   "subq %rdi,%rcx\n\t"
                   "xorl %eax,%eax\n\t"