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libcxxrt: add padding in __cxa_allocate_* to fix alignment
The addition of the referenceCount to __cxa_allocate_exception put the unwindHeader at offset 0x58 in __cxa_exception, but it requires 16-byte alignment. In order to avoid changing the current __cxa_exception ABI (and thus breaking its consumers), add explicit padding in the allocation routines (and account for it when freeing). This is intended as a lower-risk change for FreeBSD 11. A "more correct" fix should be prepared for upstream and -CURRENT. Reviewed by: dim MFC after: 3 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D7271
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=303157
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@ -572,6 +572,19 @@ static void free_exception(char *e)
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}
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}
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#ifdef __LP64__
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/**
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* There's an ABI bug in __cxa_exception: unwindHeader requires 16-byte
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* alignment but it was broken by the addition of the referenceCount.
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* The unwindHeader is at offset 0x58 in __cxa_exception. In order to keep
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* compatibility with consumers of the broken __cxa_exception, explicitly add
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* padding on allocation (and account for it on free).
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*/
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static const int exception_alignment_padding = 8;
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#else
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static const int exception_alignment_padding = 0;
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#endif
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/**
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* Allocates an exception structure. Returns a pointer to the space that can
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* be used to store an object of thrown_size bytes. This function will use an
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@ -580,16 +593,19 @@ static void free_exception(char *e)
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*/
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extern "C" void *__cxa_allocate_exception(size_t thrown_size)
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{
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size_t size = thrown_size + sizeof(__cxa_exception);
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size_t size = exception_alignment_padding + sizeof(__cxa_exception) +
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thrown_size;
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char *buffer = alloc_or_die(size);
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return buffer+sizeof(__cxa_exception);
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return buffer + exception_alignment_padding + sizeof(__cxa_exception);
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}
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extern "C" void *__cxa_allocate_dependent_exception(void)
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{
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size_t size = sizeof(__cxa_dependent_exception);
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size_t size = exception_alignment_padding +
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sizeof(__cxa_dependent_exception);
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char *buffer = alloc_or_die(size);
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return buffer+sizeof(__cxa_dependent_exception);
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return buffer + exception_alignment_padding +
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sizeof(__cxa_dependent_exception);
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}
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/**
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@ -617,7 +633,8 @@ extern "C" void __cxa_free_exception(void *thrown_exception)
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}
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}
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free_exception(reinterpret_cast<char*>(ex));
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free_exception(reinterpret_cast<char*>(ex) -
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exception_alignment_padding);
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}
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static void releaseException(__cxa_exception *exception)
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@ -644,7 +661,8 @@ void __cxa_free_dependent_exception(void *thrown_exception)
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{
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releaseException(realExceptionFromException(reinterpret_cast<__cxa_exception*>(ex)));
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}
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free_exception(reinterpret_cast<char*>(ex));
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free_exception(reinterpret_cast<char*>(ex) -
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exception_alignment_padding);
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}
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/**
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