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[Bug 1878501] Re: qemu-i386 does not define AT_SYSINFO


From: Launchpad Bug Tracker
Subject: [Bug 1878501] Re: qemu-i386 does not define AT_SYSINFO
Date: Sun, 11 Jul 2021 04:17:15 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1878501

Title:
  qemu-i386 does not define AT_SYSINFO

Status in QEMU:
  Expired

Bug description:
  qemu-i386 does not define the AT_SYSINFO auxval when running i386
  Linux binaries.

  On most libcs, this is properly handled, but this is mandatory for the
  i686 Bionic (Android) libc or it will segfault.

  This is due to a blind assumption that getauxval(AT_SYSINFO) will
  return a valid function pointer:

  The code varies from version to version, but it looks like this:

  void *__libc_sysinfo;
  // mangled as _Z19__libc_init_sysinfov
  void __libc_init_sysinfo() {
    bool dummy;
    // __bionic_getauxval = getauxval
    __libc_sysinfo = reinterpret_cast<void *>(__bionic_getauxval(AT_SYSINFO, 
dummy));
  }

  A simple way to reproduce is to compile a basic C program against the
  NDK:

  int main(void) { return 0; }

  $ i686-linux-android-clang -static empty.c -o empty
  $ qemu-i386 -cpu max ./empty
  qemu: uncaught target signal 11 (Segmentation fault) - core dumped
  Segmentation fault

  The place where it segfaults is misleading: It will, at least on the
  current NDK, crash on __set_thread_area, this is due to it calling a
  function pointer to __libc_sysinfo returned by __kernel_syscall.

  QEMU 4.1.1 (aarch64)
  Pixel 2 XL via Termux

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