wxGTK sample app compiled by llvm crashes on arm

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1

Hello,

I am using llvm-2.7 to run a native(executable) on a arm processor.

I have built my wxGtk sample app with llvm-gcc as frontend .

I am using llvm-2.7 and llvm-gcc-4.2.

I built llvm-2.7 with:

…/llvm-2.7/configure --prefix=/home/install-llvm --enable-optimized --enable-assertions

and llvm gcc with:

…/llvm-gcc-4.2-2.7.source/configure --prefix=/home//gcc-disable-shared --enable-languages=c++,c --enable-checking --enable-llvm=/home/ llvm-objects --disable-bootstrap --disable-multilib

Now from Samples, I am compiling minimal.cpp by llvm-gcc (binary for x86) using the following commands:

Step 1. llvm-gcc -O3 -emit-llvm minimal.cpp -c -o minimal.bc wxconfig –cxxflags

Step 2. llc minimal.bc –march=arm –o minimal.s (for generating arm assembly code)

Step 3 arm_v7_vfp_le-gcc minimal.s –o minimal.native wxconfig –libs (arm compiler to compile this assembly code into native executable)

Now when I am running this native executable on my target it is crashing in g_object new(). However, if I build my application(wxGTK application) with a memory allocation using new in the very start, the same exe now would run successfully.

For your reference I am posting both the codes:

Case 1: Crash at a point when it tries to allocate memory in making an object of MyFrame in the code below.
bool MyApp::OnInit()
{
if ( !wxApp::OnInit() )
return false;
// create the main application window
MyFrame *frame = new MyFrame(_T(“Minimal wxWidgets App”));
frame->Show(true);
return true;
}

Case 2: The code below is same as above except the first line in the function body and it runs fine .
bool MyApp::OnInit()
{
char *ptr = new char[10000];
if ( !wxApp::OnInit() )
return false;
// create the main application window
MyFrame *frame = new MyFrame(_T(“Minimal wxWidgets App”));
frame->Show(true);
return true;
}

Can anybody give us an explanation for this??

How does using new in the start makes a difference??

Thanks & Regards,

Ankur Jain

Senior Software Engineer

2

I am using llvm-2.7 to run a native(executable) on a arm processor.

ARM was pretty much broken in 2.7. Consider using at least 2.8

../llvm-gcc-4.2-2.7.source/configure --prefix=/home//gcc-disable-shared --enable-languages=c++,c --enable-checking --enable-llvm=/home/ llvm-objects --disable-bootstrap --disable-multilib

You have to configure llvm-gcc as cross-arm compiler.

Step 1. llvm-gcc -O3 -emit-llvm minimal.cpp -c -o minimal.bc `wxconfig –cxxflags`
Step 2. llc minimal.bc –march=arm –o minimal.s (for generating arm assembly code)

This won't work. You're trying to codegen x86 IR for ARM.

3

Thanx for a prompt reply.

I will definitely try llvm 2.8 as per your suggestion.

However Step 1 and Step 2 are working for me in case of a simple hello world program on arm processor . Similarly I am able to run a GTK application on arm. However while running wxGTKwidget app it crashes while allocation of memory. As I mentioned earlier, If I explicitly allocate memory using new operation then everything works fine. Please let me know why do we actually fail without using new, that to a arbitrary pointer which is never used in the program.

4

memory. As I mentioned earlier, If I explicitly allocate memory using new
operation then everything works fine. Please let me know why do we actually
fail without using new, that to a arbitrary pointer which is never used in
the program.

x86 and ARM have different ABIs, so you was just lucky. You can read
e.g. http://llvm.org/docs/FAQ.html#platformindependent for more
information.

5

Thanx again …
By the way I wanted to tell you that we have the same platform(linux) on host and target.

6

You said that, You have to configure llvm-gcc as cross-arm compiler.
I am not clear what does it actually mean ??
For us , intel is the host machine and arm is the target machine .

For this you need the cross-compiler (same as for normal gcc). So,
basically configure llvm-gcc as a cross-compiler
for your target platform the same way as you're doing this with the
ordinary gcc.

7

Hello,

I still have a query. Using llvm-gcc as cross-arm compiler will generate
bytecode specific to arm.
These bytecodes will work only on arm based platforms.Is it so ??

Yes, as you already checked for x86 bytecode on ARM :slight_smile:

This would
mean that we cannot have platform independent bytecodes as found in case of
java. We would be grateful to you for any comment on this.

That's correct. C/C++ are not target neutral languages. You can read
http://llvm.org/docs/FAQ.html#platformindependent for some more info.