Re: [Qemu-discuss] How to run cross-compiled binaries using Qemuuser space emulation?

[Libo Zhou]

Hi Peter,


Thanks for your reply. Creating a dummy ld.so.cache in ${sysroot}/etc/ did the 
trick for me. It was missing.


Cheers,
Libo





------------------ Original message ------------------
From: "Peter Maydell"; 
Sendtime: Tuesday, Sep 3, 2019 4:17 PM
To: "Libo Zhou"; 
Cc: "qemu-discuss"; 
Subject: Re: [Qemu-discuss] How to run cross-compiled binaries using Qemuuser 
space emulation?



On Mon, 2 Sep 2019 at 11:34, Libo Zhou <address@hidden> wrote:
>
> I am trying to run C programs compiled for MIPS32 big-endian architecture on 
> an x86_64 host. And I am using Ubuntu 18.04 LTS.
> Then I got a segmentation fault, and here is the strace log:
>
>
> 10255 brk(NULL) = 0x00412000
> 10255 mmap2(NULL,8192,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS,-1,0) = 
> 0x7f7c8000
> 10255 uname(0x7fffe8c8) = 0
> 10255 access("/etc/ld.so.nohwcap",F_OK) = -1 errno=2 (No such file or 
> directory)
> 10255 access("/etc/ld.so.preload",R_OK) = -1 errno=2 (No such file or 
> directory)
> 10255 openat(AT_FDCWD,"/etc/ld.so.cache",O_RDONLY|O_CLOEXEC) = 3
> 10255 fstat64(3,0x7fffe518) = 0
> 10255 mmap2(NULL,106802,PROT_READ,MAP_PRIVATE,3,0) = 0x7f7ad000
> 10255 close(3) = 0
> --- SIGSEGV {si_signo=SIGSEGV, si_code=1, si_addr=0x2392d008} ---
> qemu: uncaught target signal 11 (Segmentation fault) - core dumped
> [1]    10255 segmentation fault (core dumped)  ./qemu-mips -strace test

You're running into a bug in the guest ld.so (dynamic linker).
Here it is reading the host's /etc/ld.so.cache, but the problem
is that the guest ld.so can't cope with finding a ld.so.cache
for the "wrong" endianness, and it segfaults.

You can work around this by:
 * using QEMU inside a chroot which provides a complete
   guest-binary filesystem
 * ensuring that there is at least a dummy /etc/ld.so.cache in
   the 'sysroot' where QEMU looks first for files for the guest
   (I think an empty file will do.) Usually the sysroot
   directory is specified via the -L option to QEMU (you seem
   to be specifying it via configure, but the configure
   --interp-prefix option is just setting the default value
   for the runtime -L option, so you don't have to do that.)

thanks
-- PMM