Revert "x86_64: Remove unused padding from tcbhead_t"

This reverts commit 30d3fd7f4f4bc8f767d73ad4e4b005c1bd234310.

The padding is required by Chromium's MaybeUpdateGlibcTidCache
in sandbox/linux/services/namespace_sandbox.cc.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h
index a9c348e6969c0cf63284073b76178e09aacde4c5..551d342d52117131b0b7e0dc4517f108ded07aec 100644 (file)
--- a/sysdeps/x86_64/nptl/tls.h
+++ b/sysdeps/x86_64/nptl/tls.h
@@ -62,16 +62,28 @@ typedef struct
   void *__private_ss;
   /* The marker for the current shadow stack.  */
   unsigned long long int ssp_base;
+  /* Must be kept even if it is no longer used by glibc since programs,
+     like AddressSanitizer, depend on the size of tcbhead_t.  */
+  __128bits __glibc_unused2[8][4] __attribute__ ((aligned (32)));
+
+  void *__padding[8];
 } tcbhead_t;
 
 # ifdef __ILP32__
 /* morestack.S in libgcc uses offset 0x40 to access __private_ss,   */
 _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x40,
                "offset of __private_ss != 0x40");
+/* NB: ssp_base used to be "long int __glibc_reserved2", which was
+   changed from 32 bits to 64 bits.  Make sure that the offset of the
+   next field, __glibc_unused2, is unchanged.  */
+_Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x60,
+               "offset of __glibc_unused2 != 0x60");
 # else
 /* morestack.S in libgcc uses offset 0x70 to access __private_ss,   */
 _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x70,
                "offset of __private_ss != 0x70");
+_Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
+               "offset of __glibc_unused2 != 0x80");
 # endif
 
 #else /* __ASSEMBLER__ */