[Bug 1918302] Re: qemu-system-arm segfaults while servicing SYS_HEAPINFO

[Simon Tatham]

Oops – naturally, I realised just *after* hitting send that it would
have been a good idea to say exactly which git commit I was testing on.
It was 9e2e9fe3df9f539f8b6941ceb96d25355fdae47e .

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https://bugs.launchpad.net/bugs/1918302

Title:
  qemu-system-arm segfaults while servicing SYS_HEAPINFO

Status in QEMU:
  Fix Committed

Bug description:
  I compiled QEMU version 5.2.0 from source on Ubuntu 18.04, and tried
  to use it to run the attached bare-metal Arm hello-world image, using
  the command line

  qemu-system-arm -M microbit -semihosting -nographic -device
  loader,file=hello.hex

  The result was that qemu-system-arm itself died of a segfault.
  Compiling it for debugging, the location of the segfault was in
  target/arm/arm-semi.c, in the case handler for the semihosting call
  TARGET_SYS_HEAPINFO, on line 1020 which assigns to 'rambase':

              const struct arm_boot_info *info = env->boot_info;
              target_ulong rambase = info->loader_start;

  and the problem seems to be that 'info', aka env->boot_info, is NULL
  in this context.

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