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Revert "x86_64: Remove unused padding from tcbhead_t"

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This reverts commit 30d3fd7f4f.

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

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Florian Weimer 2025-01-07 08:34:13 +01:00
parent c4ed6a380e
commit a257f201dd
1 changed files with 12 additions and 0 deletions
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12
sysdeps/x86_64/nptl/tls.h
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@ -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__ */