[LLVMdev] Invalid call generated on 64-bit linux when calling native C function from IR

[Jan Rehders]

Hi,

when I try to generate LLVM-IR which calls back to native C functions the
jit compiler generates invalid code on 64-bit linux. The same code works
fine on 32-bit linux, 32-bit OS X and 64-bit OS X. A reproduction case is
attached to this mail. It is a simple modification of the "How to use jit"
example adding a call to a native function.

I am currently using EE->addGlobalMapping to register the native functions.
This appears to be nessecary because the native functions will be part of a
.so/.dylib so the jit will not find them using dlsym on linux and we would
prefer to stripp all symbols.

I'm using LLVM 2.4, which I compiled using EXTRA_OPTIONS="-m64/-m32 -fPIC".

Below you can see the code generated by the jit on different platforms. On
64-bit linux the 'call' instruction uses a completely wrong address. This
invalid address appears to be related to the address of the call instruction
itself (e.g. it is always a 'close' address). To my knowledge the call
instruction's address argument is a relative address and thus needs to be
within 2^24 bytes of the instruction. It looks like the code generator
should generate a jump using a function pointer in this situation and fails
to handle this.

Am I doing something wrong in my code or is this an LLVM bug?

Jan

Linux 64-bit:
(gdb) print addone_addr
$1 = (void *) 0x406018
(gdb) x/10i foo_addr
0x2b7184072030:    sub    $0x8,%rsp
0x2b7184072034:    mov    $0x14,%edi
0x2b7184072039:    callq  0x2b7200406018 <--- absolutely not ok
0x2b718407203e:    add    $0x8,%rsp
0x2b7184072042:    retq
(gdb) x/10i nfoo_addr
0x40603a <nativefoo>:    push   %rbp
0x40603b <nativefoo+1>:    mov    %rsp,%rbp
0x40603e <nativefoo+4>:    mov    $0x1e,%edi
0x406043 <nativefoo+9>:    callq  0x406018 <addOne> <--- ok
0x406048 <nativefoo+14>:    leaveq
0x406049 <nativefoo+15>:    retq

OS X 64-bit:
(gdb) print addone_addr
$1 = (void *) 0x100000d56
(gdb) x/10i foo_addr
x/10i foo_addr
0x102080030:    sub    $0x8,%rsp
0x102080034:    mov    $0x14,%edi
0x102080039:    callq  0x100000d56 <addOne> <--- ok
0x10208003e:    add    $0x8,%rsp
0x102080042:    retq
(gdb) x/10i nfoo_addr
x/10i nfoo_addr
0x100000d78 <nativefoo>:    push   %rbp
0x100000d79 <nativefoo+1>:    mov    %rsp,%rbp
0x100000d7c <nativefoo+4>:    mov    $0x1e,%edi
0x100000d81 <nativefoo+9>:    callq  0x100000d56 <addOne> <--- ok
0x100000d86 <nativefoo+14>:    leaveq
0x100000d87 <nativefoo+15>:    retq

Linux 32-bit:
(gdb) print addone_addr
print addone_addr
$1 = (void *) 0x805aa74
(gdb) x/10i foo_addr
x/10i foo_addr
0xc26020:    sub    $0x4,%esp
0xc26023:    movl   $0x14,(%esp)
0xc2602a:    call   0x805aa74 <addOne> <--- ok
0xc2602f:    add    $0x4,%esp
0xc26032:    ret
(gdb) x/10i nfoo_addr
x/10i nfoo_addr
0x805aa8c <nativefoo>:    push   %ebp
0x805aa8d <nativefoo+1>:    mov    %esp,%ebp
0x805aa8f <nativefoo+3>:    push   $0x1e
0x805aa91 <nativefoo+5>:    call   0x805aa74 <addOne> <--- ok
0x805aa96 <nativefoo+10>:    add    $0x4,%esp
0x805aa99 <nativefoo+13>:    leave
0x805aa9a <nativefoo+14>:    ret

OS X 32-bit:
(gdb) print addone_addr
print addone_addr
$1 = (void *) 0x1e62
(gdb) x/10i foo_addr
x/10i foo_addr
0x2080020:    sub    $0xc,%esp
0x2080023:    movl   $0x14,(%esp)
0x208002a:    call   0x1e62 <addOne> <--- ok
0x208002f:    add    $0xc,%esp
0x2080032:    ret
(gdb) x/10i nfoo_addr
x/10i nfoo_addr
0x1e80 <nativefoo>:    push   %ebp
0x1e81 <nativefoo+1>:    mov    %esp,%ebp
0x1e83 <nativefoo+3>:    sub    $0x18,%esp
0x1e86 <nativefoo+6>:    movl   $0x1e,(%esp)
0x1e8d <nativefoo+13>:    call   0x1e62 <addOne> <--- ok
0x1e92 <nativefoo+18>:    leave
0x1e93 <nativefoo+19>:    ret
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