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[Bug 1878501] Re: qemu-i386 does not define AT_SYSINFO
From: |
Richard Henderson |
Subject: |
[Bug 1878501] Re: qemu-i386 does not define AT_SYSINFO |
Date: |
Thu, 14 May 2020 15:31:49 -0000 |
We do not define AT_SYSINFO because we do not implement the vdso.
All we have so far is the vsyscall page, which is not the same thing.
I've had patches for the vdso for a number of years; perhaps it's
time to update and re-send that...
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https://bugs.launchpad.net/bugs/1878501
Title:
qemu-i386 does not define AT_SYSINFO
Status in QEMU:
New
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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