[Qemu-discuss] How to run cross-compiled binaries using Qemu user space emulation

[Libo Zhou]

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.


I installed the prebuilt cross compiler using the following command:


$ sudo apt install gcc-mips-linux-gnu


Then, I built Qemu from source with the commands below:


$ cd qemu-4.1.0
$ mkdir build
$ cd build
$ ../configure --interp-prefiix=/usr/mips-linux-gnu 
--target-list=mips-linux-user # if I don't set up the prefix then I will get a 
/lib/ld.so.1 not found error later

$ make -j4 # my machine has 4 cpu's



After that, I went into the qemu binary directory, and created a very simple C 
program:

 
$ cd mips-linux-user
$ echo "int main(void) { return 0; }" > test.c

$ mips-linux-gnu-gcc test.c -o test # cross-compile MIPS on x86_64


I checked the filetype of my MIPS ELF using the command:


$ file test
test: ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1 (SYSV), 
dynamically linked, interpreter /lib/ld., for GNU/Linux 3.2.0, 
BuildID[sha1]=02eaa87216ede002d62050f205d5764b68fabdf6, not stripped



After running with the command:


$ ./qemu-mips -strace test


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



I am sorry if my question sounds too rookie, but I am having trouble getting 
things to work. Any help would be appreciated.


Thanks,
Libo

[Qemu-discuss] How to run cross-compiled binaries using Qemu user space emulation?

[Libo Zhou]

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.


I installed the prebuilt cross compiler using the following command:


$ sudo apt install gcc-mips-linux-gnu


Then, I built Qemu from source with the commands below:


$ cd qemu-4.1.0
$ mkdir build
$ cd build
$ ../configure --interp-prefiix=/usr/mips-linux-gnu 
--target-list=mips-linux-user # if I don't set up the prefix then I will get a 
/lib/ld.so.1 not found error later

$ make -j4 # my machine has 4 cpu's



After that, I went into the qemu binary directory, and created a very simple C 
program:

 
$ cd mips-linux-user
$ echo "int main(void) { return 0; }" > test.c

$ mips-linux-gnu-gcc test.c -o test # cross-compile MIPS on x86_64


I checked the filetype of my MIPS ELF using the command:


$ file test
test: ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1 (SYSV), 
dynamically linked, interpreter /lib/ld., for GNU/Linux 3.2.0, 
BuildID[sha1]=02eaa87216ede002d62050f205d5764b68fabdf6, not stripped



After running with the command:


$ ./qemu-mips -strace test


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



I am sorry if my question sounds too rookie, but I am having trouble getting 
things to work. Any help would be appreciated.


Thanks,
Libo

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

[Libo Zhou]

The solution is:


$ cd /usr/mips-linux-gnu
$ sudo mkdir etc
$ sudo ldconfig -C etc/ld.so.cache -r .


(Credit: Aleksandar Markovic at Qemu-devel)



-- Original --
From:  "Libo Zhou";;
Send time: Monday, Sep 2, 2019 6:21 PM
To: "qemu-discuss"; 

Subject:  How to run cross-compiled binaries using Qemu user space emulation



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.


I installed the prebuilt cross compiler using the following command:


$ sudo apt install gcc-mips-linux-gnu


Then, I built Qemu from source with the commands below:


$ cd qemu-4.1.0
$ mkdir build
$ cd build
$ ../configure --interp-prefiix=/usr/mips-linux-gnu 
--target-list=mips-linux-user # if I don't set up the prefix then I will get a 
/lib/ld.so.1 not found error later

$ make -j4 # my machine has 4 cpu's



After that, I went into the qemu binary directory, and created a very simple C 
program:

 
$ cd mips-linux-user
$ echo "int main(void) { return 0; }" > test.c

$ mips-linux-gnu-gcc test.c -o test # cross-compile MIPS on x86_64


I checked the filetype of my MIPS ELF using the command:


$ file test
test: ELF 32-bit MSB executable, MIPS, MIPS32 rel2 version 1 (SYSV), 
dynamically linked, interpreter /lib/ld., for GNU/Linux 3.2.0, 
BuildID[sha1]=02eaa87216ede002d62050f205d5764b68fabdf6, not stripped



After running with the command:


$ ./qemu-mips -strace test


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



I am sorry if my question sounds too rookie, but I am having trouble getting 
things to work. Any help would be appreciated.


Thanks,
Libo

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  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

[Qemu-discuss] What is inside in_asm log exactly

[Libo Zhou]

I have noticed that I can log some useful information using the "-d" switch. I 
tried logging in_asm out of curiosity and found out that there is a massive 
amount of assembly in the log (10,000+ lines). The assembly generated by gcc 
doesn't have so many lines (10+ lines).

[Qemu-discuss] Why my mails are not sent to the list sometimes

[Libo Zhou]

This happens very rarely, but it is now becoming problematic. I've been waiting 
for some responses for days, only to finally realize my mails were not sent to 
the list. What would be the possible reason for that? I can still receive the 
list emails.


Well, what if this one can't go to the list? -_-|||

Initialize data memory in user space emulation

[Libo Zhou]

Hi all,

I need a way to manipulate data saved in a reserved memory region in linux user 
space emulation. I found the -B option very promising.  Documentation says it 
is useful when the address region required by guest applications is reserved on 
the host.

But how can I initialize that memory with data?