From b8ecbaaac0f9ff9682a310cc78616d421470335e Mon Sep 17 00:00:00 2001
From: Corinna Vinschen <corinna@vinschen.de>
Date: Tue, 7 Apr 2020 17:41:05 +0200
Subject: [PATCH] Cygwin: threads: use extended memory API if available

So far Cygwin was jumping through hoops to restrict memory
allocation to specific regions.  With the advent of VirtualAlloc2
and MapViewOfFile3 (and it's NT counterpart NtMapViewOfSectionEx),
we can skip searching for free space in the specific regions
and just call these functions and let the OS do the job more
efficiently and less racy.

Use VirtualAlloc2 on W10 1803 and later in thread stack allocation.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
---
 winsup/cygwin/miscfuncs.cc | 51 +++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/winsup/cygwin/miscfuncs.cc b/winsup/cygwin/miscfuncs.cc
index b4ab7cd7d..cba2140b6 100644
--- a/winsup/cygwin/miscfuncs.cc
+++ b/winsup/cygwin/miscfuncs.cc
@@ -508,9 +508,45 @@ pthread_wrapper (PVOID arg)
 class thread_allocator
 {
   UINT_PTR current;
-public:
-  thread_allocator () : current (THREAD_STORAGE_HIGH) {}
-  PVOID alloc (SIZE_T size)
+  PVOID (thread_allocator::*alloc_func) (SIZE_T);
+  PVOID _alloc (SIZE_T size)
+  {
+    MEM_ADDRESS_REQUIREMENTS thread_req = {
+      (PVOID) THREAD_STORAGE_LOW,
+      (PVOID) (THREAD_STORAGE_HIGH - 1),
+      THREAD_STACK_SLOT
+    };
+    MEM_EXTENDED_PARAMETER thread_ext = {
+      .Type = MemExtendedParameterAddressRequirements,
+      .Pointer = (PVOID) &thread_req
+    };
+    SIZE_T real_size = roundup2 (size, THREAD_STACK_SLOT);
+    PVOID real_stackaddr = NULL;
+
+    if (real_size <= THREAD_STACK_MAX)
+      real_stackaddr = VirtualAlloc2 (GetCurrentProcess(), NULL, real_size,
+				      MEM_RESERVE | MEM_TOP_DOWN,
+				      PAGE_READWRITE, &thread_ext, 1);
+    /* If the thread area allocation failed, or if the application requests a
+       monster stack, fulfill request from mmap area. */
+    if (!real_stackaddr)
+      {
+	MEM_ADDRESS_REQUIREMENTS mmap_req = {
+	  (PVOID) MMAP_STORAGE_LOW,
+	  (PVOID) (MMAP_STORAGE_HIGH - 1),
+	  THREAD_STACK_SLOT
+	};
+	MEM_EXTENDED_PARAMETER mmap_ext = {
+	  .Type = MemExtendedParameterAddressRequirements,
+	  .Pointer = (PVOID) &mmap_req
+	};
+	real_stackaddr = VirtualAlloc2 (GetCurrentProcess(), NULL, real_size,
+					MEM_RESERVE | MEM_TOP_DOWN,
+					PAGE_READWRITE, &mmap_ext, 1);
+      }
+    return real_stackaddr;
+  }
+  PVOID _alloc_old (SIZE_T size)
   {
     SIZE_T real_size = roundup2 (size, THREAD_STACK_SLOT);
     BOOL overflow = FALSE;
@@ -558,6 +594,15 @@ public:
       set_errno (EAGAIN);
     return real_stackaddr;
   }
+public:
+  thread_allocator () : current (THREAD_STORAGE_HIGH)
+  {
+    alloc_func = wincap.has_extended_mem_api () ? &_alloc : &_alloc_old;
+  }
+  PVOID alloc (SIZE_T size)
+  {
+    return (this->*alloc_func) (size);
+  }
 };
 
 thread_allocator thr_alloc NO_COPY;