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[Qemu-devel] [Bug 883133] Re: qemu on ARM hosts asserts due to code buff


From: Michael Hope
Subject: [Qemu-devel] [Bug 883133] Re: qemu on ARM hosts asserts due to code buffer/libc heap conflict
Date: Thu, 05 Jan 2012 00:58:18 -0000

** Changed in: qemu-linaro
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/883133

Title:
  qemu on ARM hosts asserts due to code buffer/libc heap conflict

Status in QEMU:
  Fix Committed
Status in Linaro QEMU:
  Fix Committed

Bug description:
  On ARM hosts qemu (about half the time) asserts on startup:

  qemu-system-i386: malloc.c:3096: sYSMALLOc: Assertion `(old_top == 
(((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) -
  __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || 
((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct 
malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * 
(sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end 
& pagemask) == 0)' failed.

  This turns out to be because code_gen_alloc() is using mmap(MAP_FIXED)
  to map the code buffer at address 0x01000000UL, which is in the area
  glibc happens to be using for its heap. This tends to make the next
  malloc() abort, although occasionally the stars align and we pass that
  and fail weirdly later on.

  I suspect we need to drop the MAP_FIXED requirement and fix the TCG code to 
cope with emitting code for longer-range
  branches for calls to host fns etc (calls/branches within the generated code 
should be ok to keep using the short-range
  branch insn I think). There is already no guarantee that the generated code 
and the host C code are within short
  branch range of each other...

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