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AK+LibJS: Handle NaN-boxing pointers on AArch64

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JS::Value stores 48 bit pointers to separately allocated objects in its
payload. On x86-64, canonical addresses have their top 16 bits set to
the same value as bit 47, effectively meaning that the value has to be
sign-extended to get the pointer. AArch64, however, expects the topmost
bits to be all zeros.

This commit gates sign extension behind `#if ARCH(X86_64)`, and adds an
`#error` for unsupported architectures, so that we do not forget to
think about pointer handling when porting to a new architecture.

Fixes #15290
Fixes SerenityOS/ladybird#56
This commit is contained in:
Daniel Bertalan 2022-09-20 18:09:33 +02:00 • committed by Andreas Kling
parent 62fed2a31d
commit 2b69af2dfe
4 changed files with 42 additions and 24 deletions
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6
AK/Platform.h
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@ -18,6 +18,12 @@
# define AK_ARCH_AARCH64 1
#endif
#if (defined(__SIZEOF_POINTER__) && __SIZEOF_POINTER__ == 8) || defined(_WIN64)
# define AK_ARCH_64_BIT
#else
# define AK_ARCH_32_BIT
#endif
#if defined(__APPLE__) && defined(__MACH__)
# define AK_OS_MACOS
# define AK_OS_BSD_GENERIC