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Re: [PATCH v5 0/4] linux-user: Fix siginfo_t contents when jumping to no

From: Ilya Leoshkevich
Subject: Re: [PATCH v5 0/4] linux-user: Fix siginfo_t contents when jumping to non-readable pages
Date: Thu, 18 Aug 2022 20:28:39 +0200
User-agent: Evolution 3.42.4 (3.42.4-2.fc35)

On Fri, 2022-08-19 at 00:55 +0800, Vivian Wang wrote:
> Hi,
> Could this be related to issue 1155 [1]? On RISC-V, I'm getting
> incorrect [m|s]tval/[m|s]epc combinations for page faults in system
> emulation and incorrect si_addr and program counter on SIGSEGV in
> user emulation. Since it seems to only affect instructions that cross
> page boundaries, and RISC-V also has variable length instructions, it
> seems that I've run into the same problem as what is fixed here.
> Could this fix be extended be extended to targets/riscv?
> dram
> [1]: https://gitlab.com/qemu-project/qemu/-/issues/1155

Yes, this looks quite similar.
I'm not too familiar with riscv, but I just googled [1].
If the following is correct:

However, the instruction set reserves enough opcode space to make it
possible to differentiate between 16-bit, 32-bit, 48-bit, and 64-bit
instructions.  Instructions that start with binary 11 (in the lowest
bit position of the instruction) are 32-bit sized instructions (but one
pattern is reserved: so they cannot start with 11111).  The compact
instructions use 00, 01, and 10 in that same position.  48-bit
instructions use starting sequence 011111, and 64-bit instructions
start with 0111111.

then we can fix this the same way s390x is being fixed here.


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