src/os_cpu/linux_x86/vm/os_linux_x86.cpp

rev 8517 : 8078513: [linux]  Clean up code relevant to LinuxThreads implementation
Reviewed-by: dholmes, sla, coleenp

*** 1,7 ****
  /*
!  * Copyright (c) 1999, 2014, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
--- 1,7 ----
  /*
!  * Copyright (c) 1999, 2015, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
*** 617,673 ****
  ////////////////////////////////////////////////////////////////////////////////
  // thread stack
  
  #ifdef AMD64
  size_t os::Linux::min_stack_allowed  = 64 * K;
- 
- // amd64: pthread on amd64 is always in floating stack mode
- bool os::Linux::supports_variable_stack_size() {  return true; }
  #else
  size_t os::Linux::min_stack_allowed  =  (48 DEBUG_ONLY(+4))*K;
  
! #ifdef __GNUC__
! #define GET_GS() ({int gs; __asm__ volatile("movw %%gs, %w0":"=q"(gs)); gs&0xffff;})
! #endif
! 
! // Test if pthread library can support variable thread stack size. LinuxThreads
! // in fixed stack mode allocates 2M fixed slot for each thread. LinuxThreads
! // in floating stack mode and NPTL support variable stack size.
  bool os::Linux::supports_variable_stack_size() {
-   if (os::Linux::is_NPTL()) {
-      // NPTL, yes
       return true;
- 
-   } else {
-     // Note: We can't control default stack size when creating a thread.
-     // If we use non-default stack size (pthread_attr_setstacksize), both
-     // floating stack and non-floating stack LinuxThreads will return the
-     // same value. This makes it impossible to implement this function by
-     // detecting thread stack size directly.
-     //
-     // An alternative approach is to check %gs. Fixed-stack LinuxThreads
-     // do not use %gs, so its value is 0. Floating-stack LinuxThreads use
-     // %gs (either as LDT selector or GDT selector, depending on kernel)
-     // to access thread specific data.
-     //
-     // Note that %gs is a reserved glibc register since early 2001, so
-     // applications are not allowed to change its value (Ulrich Drepper from
-     // Redhat confirmed that all known offenders have been modified to use
-     // either %fs or TSD). In the worst case scenario, when VM is embedded in
-     // a native application that plays with %gs, we might see non-zero %gs
-     // even LinuxThreads is running in fixed stack mode. As the result, we'll
-     // return true and skip _thread_safety_check(), so we may not be able to
-     // detect stack-heap collisions. But otherwise it's harmless.
-     //
- #ifdef __GNUC__
-     return (GET_GS() != 0);
- #else
-     return false;
- #endif
-   }
  }
- #endif // AMD64
  
  // return default stack size for thr_type
  size_t os::Linux::default_stack_size(os::ThreadType thr_type) {
    // default stack size (compiler thread needs larger stack)
  #ifdef AMD64
--- 617,634 ----
  ////////////////////////////////////////////////////////////////////////////////
  // thread stack
  
  #ifdef AMD64
  size_t os::Linux::min_stack_allowed  = 64 * K;
  #else
  size_t os::Linux::min_stack_allowed  =  (48 DEBUG_ONLY(+4))*K;
+ #endif // AMD64
  
! // Test if pthread library can support variable thread stack size.
  bool os::Linux::supports_variable_stack_size() {
    return true;
  }
  
  // return default stack size for thr_type
  size_t os::Linux::default_stack_size(os::ThreadType thr_type) {
    // default stack size (compiler thread needs larger stack)
  #ifdef AMD64