在2024年9月5日九月 下午10:15，Charlie Jenkins写道： > Some applications rely on placing data in free bits addresses allocated > by mmap. Various architectures (eg. x86, arm64, powerpc) restrict the > address returned by mmap to be less than the 48-bit address space, > unless the hint address uses more than 47 bits (the 48th bit is reserved > for the kernel address space). > > The riscv architecture needs a way to similarly restrict the virtual > address space. On the riscv port of OpenJDK an error is thrown if > attempted to run on the 57-bit address space, called sv57 [1]. golang > has a comment that sv57 support is not complete, but there are some > workarounds to get it to mostly work [2]. > > These applications work on x86 because x86 does an implicit 47-bit > restriction of mmap() address that contain a hint address that is less > than 48 bits. > > Instead of implicitly restricting the address space on riscv (or any > current/future architecture), provide a flag to the personality syscall > that can be used to ensure an application works in any arbitrary VA > space. A similar feature has already been implemented by the personality > syscall in ADDR_LIMIT_32BIT. > > This flag will also allow seemless compatibility between all > architectures, so applications like Go and OpenJDK that use bits in a > virtual address can request the exact number of bits they need in a > generic way. The flag can be checked inside of vm_unmapped_area() so > that this flag does not have to be handled individually by each > architecture. Tested-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> Tested on MIPS VA 48 system, fixed pointer tagging on mozjs! Thanks! [...] -- - Jiaxun
