RFC: Linux/i386: Set TARGET_THREAD_SPLIT_STACK_OFFSET to 0x34

Message ID 20180530121305.GA43637@intel.com
State New
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Series
  • RFC: Linux/i386: Set TARGET_THREAD_SPLIT_STACK_OFFSET to 0x34
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Commit Message

H.J. Lu May 30, 2018, 12:13 p.m.
TARGET_THREAD_SPLIT_STACK_OFFSET has been wrong for Linux/i386 from
the start.  Should we change glibc for GCC's mistake or fix GCC?


H.J.
---
In glibc, sysdeps/i386/nptl/tls.h has

typedef struct
{
  void *tcb;            /* Pointer to the TCB.  Not necessarily the
                           thread descriptor used by libpthread.  */
  dtv_t *dtv;
  void *self;           /* Pointer to the thread descriptor.  */
  int multiple_threads;
  uintptr_t sysinfo;
  uintptr_t stack_guard;
  uintptr_t pointer_guard;
  int gscope_flag;
  int __glibc_reserved1;
  /* Reservation of some values for the TM ABI.  */
  void *__private_tm[4];
  /* GCC split stack support.  */
  void *__private_ss;
} tcbhead_t;

Update i386 TARGET_THREAD_SPLIT_STACK_OFFSET to 0x34 to match the offset
of __private_ss.

	PR target/85990
	* config/i386/gnu-user.h (TARGET_THREAD_SPLIT_STACK_OFFSET): Set
	to 0x34.
	* config/i386/gnu-user64.h (TARGET_THREAD_SPLIT_STACK_OFFSET):
	Set to 0x34 for -m32.
---
 gcc/config/i386/gnu-user.h   | 4 ++--
 gcc/config/i386/gnu-user64.h | 6 ++++--
 2 files changed, 6 insertions(+), 4 deletions(-)

-- 
2.17.0

Patch

diff --git a/gcc/config/i386/gnu-user.h b/gcc/config/i386/gnu-user.h
index d1dad685e72..7d061f392ea 100644
--- a/gcc/config/i386/gnu-user.h
+++ b/gcc/config/i386/gnu-user.h
@@ -134,6 +134,6 @@  along with GCC; see the file COPYING3.  If not see
 /* i386 glibc provides __stack_chk_guard in %gs:0x14.  */
 #define TARGET_THREAD_SSP_OFFSET	0x14
 
-/* We steal the last transactional memory word.  */
-#define TARGET_THREAD_SPLIT_STACK_OFFSET 0x30
+/* i386 glibc provides __private_ss in %gs:0x34.  */
+#define TARGET_THREAD_SPLIT_STACK_OFFSET 0x34
 #endif
diff --git a/gcc/config/i386/gnu-user64.h b/gcc/config/i386/gnu-user64.h
index 491416fec0c..47d6a3bf34c 100644
--- a/gcc/config/i386/gnu-user64.h
+++ b/gcc/config/i386/gnu-user64.h
@@ -86,9 +86,11 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define TARGET_THREAD_SSP_OFFSET \
   (TARGET_64BIT ? (TARGET_X32 ? 0x18 : 0x28) : 0x14)
 
-/* We steal the last transactional memory word.  */
+/* i386 glibc provides __private_ss in %gs:0x34,
+   x32 glibc provides it in %fs:0x40.
+   x86_64 glibc provides it in %fs:0x70.  */
 #define TARGET_THREAD_SPLIT_STACK_OFFSET \
-  (TARGET_64BIT ? (TARGET_X32 ? 0x40 : 0x70) : 0x30)
+  (TARGET_64BIT ? (TARGET_X32 ? 0x40 : 0x70) : 0x34)
 #endif
 
 #undef WCHAR_TYPE