Revert "[compiler-rt] [builtins] Remove unused/misnamed x86 chkstk functions"

compiler-rt/lib/builtins/CMakeLists.txt

@@ -389,6 +389,7 @@ if (NOT MSVC)
     set(i386_SOURCES
       ${i386_SOURCES}
       i386/chkstk.S
+      i386/chkstk2.S
     )
   endif()
 else () # MSVC

compiler-rt/lib/builtins/i386/chkstk.S

@@ -4,19 +4,24 @@
 
 #include "../assembly.h"
 
-#ifdef __i386__
-
-// _chkstk (_alloca) routine - probe stack between %esp and (%esp-%eax) in 4k increments,
-// then decrement %esp by %eax.  Preserves all registers except %esp and flags.
+// _chkstk routine
 // This routine is windows specific
 // http://msdn.microsoft.com/en-us/library/ms648426.aspx
+//
+// This function does not decrement %esp at the end.
+
+// GCC after 4.6 generates calls to "___chkstk_ms". For other variants of
+// this function, which do decrement %esp, see chkstk2.S.
+
+#ifdef __i386__
 
 .text
 .balign 4
-DEFINE_COMPILERRT_FUNCTION(_alloca) // _chkstk and _alloca are the same function
+DEFINE_COMPILERRT_FUNCTION(__chkstk_ms)
         push   %ecx
+        push   %eax
         cmp    $0x1000,%eax
-        lea    8(%esp),%ecx     // esp before calling this routine -> ecx
+        lea    12(%esp),%ecx
         jb     1f
 2:
         sub    $0x1000,%ecx
@@ -27,13 +32,9 @@ DEFINE_COMPILERRT_FUNCTION(_alloca) // _chkstk and _alloca are the same function
 1:
         sub    %eax,%ecx
         test   %ecx,(%ecx)
-
-        lea    4(%esp),%eax     // load pointer to the return address into eax
-        mov    %ecx,%esp        // install the new top of stack pointer into esp
-        mov    -4(%eax),%ecx    // restore ecx
-        push   (%eax)           // push return address onto the stack
-        sub    %esp,%eax        // restore the original value in eax
+        pop    %eax
+        pop    %ecx
         ret
-END_COMPILERRT_FUNCTION(_alloca)
+END_COMPILERRT_FUNCTION(__chkstk_ms)
 
 #endif // __i386__

compiler-rt/lib/builtins/i386/chkstk2.S

@@ -0,0 +1,57 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "../assembly.h"
+
+#ifdef __i386__
+
+// _chkstk (_alloca) routine - probe stack between %esp and (%esp-%eax) in 4k increments,
+// then decrement %esp by %eax.  Preserves all registers except %esp and flags.
+// This routine is windows specific
+// http://msdn.microsoft.com/en-us/library/ms648426.aspx
+
+// Clang on i386 mingw generates calls to "_alloca" (which gets decorated to
+// "__alloca").
+//
+// GCC before 4.6 generated calls a symbol which after decoration is named
+// "___chkstk", with three leading underscores. We provide that here as well.
+//
+// MSVC produces calls to the symbol "__chkstk", with two leading underscores.
+// That one has the same signature as this one - but we don't provide that
+// symbol here. (If we'd do that, we should do it in a separate object file
+// to avoid potential symbol collisions - see
+// commit 248aeac1ad2cf4f583490dd1312a5b448d2bb8cc for details.)
+//
+// GCC after 4.6 generates calls to "___chkstk_ms", which does not decrement
+// %esp - that function is defined in chkstk.S.
+
+.text
+.balign 4
+DEFINE_COMPILERRT_FUNCTION(_alloca) // _chkstk and _alloca are the same function
+// This gets decorated into "___chkstk"; GCC < 4.6 references this symbol.
+DEFINE_COMPILERRT_FUNCTION(__chkstk)
+        push   %ecx
+        cmp    $0x1000,%eax
+        lea    8(%esp),%ecx     // esp before calling this routine -> ecx
+        jb     1f
+2:
+        sub    $0x1000,%ecx
+        test   %ecx,(%ecx)
+        sub    $0x1000,%eax
+        cmp    $0x1000,%eax
+        ja     2b
+1:
+        sub    %eax,%ecx
+        test   %ecx,(%ecx)
+
+        lea    4(%esp),%eax     // load pointer to the return address into eax
+        mov    %ecx,%esp        // install the new top of stack pointer into esp
+        mov    -4(%eax),%ecx    // restore ecx
+        push   (%eax)           // push return address onto the stack
+        sub    %esp,%eax        // restore the original value in eax
+        ret
+END_COMPILERRT_FUNCTION(__chkstk)
+END_COMPILERRT_FUNCTION(_alloca)
+
+#endif // __i386__