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[Bug 1905356] Re: No check for unaligned data access in ARM32 instructio


From: Richard Henderson
Subject: [Bug 1905356] Re: No check for unaligned data access in ARM32 instructions
Date: Wed, 25 Nov 2020 03:18:14 -0000

** Changed in: qemu
     Assignee: (unassigned) => Richard Henderson (rth)

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https://bugs.launchpad.net/bugs/1905356

Title:
  No check for unaligned data access in ARM32 instructions

Status in QEMU:
  Confirmed

Bug description:
  hi

  According to the ARM documentation, there are alignment requirements
  of load/store instructions.  Alignment fault should be raised if the
  alignment check is failed. However, it seems that QEMU doesn't
  implement this, which is against the documentation of ARM. For
  example, the instruction LDRD/STRD/LDREX/STREX must check the address
  is word alignment no matter what value the SCTLR.A is.

  I attached a testcase, which contains an instruction at VA 0x10240:
  ldrd r0,[pc.#1] in the main function. QEMU can successfully load the
  data in the unaligned address. The test is done in QEMU 5.1.0. I can
  provide more testcases for the other instructions if you need. Many
  thanks.

  To patch this, we need a check while we translate the instruction to
  tcg. If the address is unaligned, a signal number (i.e., SIGBUS)
  should be raised.

  Regards
  Muhui

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