What does “BUS_ADRALN - Invalid address alignment”

问题:

We are on HPUX and my code is in C++. We are getting

BUS_ADRALN - Invalid address alignment

in our executable on a function call. What does this error means? Same function is working many times then suddenly its giving core dump. in GDB when I try to print the object values it says not in context. Any clue where to check?

回答1:

You are having a data alignment problem. This is likely caused by trying to read or write through a bad pointer of some kind.

A data alignment problem is when the address a pointer is pointing at isn't 'aligned' properly. For example, some architectures (the old Cray 2 for example) require that any attempt to read anything other than a single character from memory only occur through a pointer in which the last 3 bits of the pointer's value are 0. If any of the last 3 bits are 1, the hardware will generate an alignment fault which will result in the kind of problem you're seeing.

Most architectures are not nearly so strict, and frequently the required alignment depends on the exact type being accessed. For example, a 32 bit integer might require only the last 2 bits of the pointer to be 0, but a 64 bit float might require the last 3 bits to be 0.

Alignment problems are usually caused by the same kinds of problems that would cause a SEGFAULT or segmentation fault. Usually a pointer that isn't initialized. But it could be caused by a bad memory allocator that isn't returning pointers with the proper alignment, or by the result of pointer arithmetic on the pointer when it isn't of the correct type.

The system implementation of malloc and/or operator new are almost certainly correct or your program would be crashing way before it currently does. So I think the bad memory allocator is the least likely tree to go barking up. I would check first for an uninitialized pointer and then bad pointer arithmetic.

As a side note, the x86 and x86_64 architectures don't have any alignment requirements. But, because of how cache lines work, and for various other reasons, it's often a good idea for performance to align your data on a boundary that's as big as the datatype being stored (i.e. a 4 byte boundary for a 32 bit int).

回答2:

Most processors (not x86 and friends.. the blacksheep of the family lol) require accesses to certain elements to be aligned on multiples of bytes. I.e. if you read an integer from address 0x04 that is okay, but if you try to do the same from 0x03 you will cause an interrupt to be thrown.

This is because it's easier to implement the load/store hardware if it's always on a multiple of the data size with which you're working.

Since HP-UX runs only on RISC processors, which typically have such constraints, you should see here -> http://en.wikipedia.org/wiki/Data_structure_alignment#RISC.

回答3:

Actually HP-UX has its own great forum on ITRC and some HP staff members are very helpful. I just took a look at the same topic you are asking and here are some results. For example the similar problem was caused actually by a bad input parameter. I strongly advise you first to read answers to similar question and if necessary to post your question there.

By the way it is likely that you will be asked to post results of these gdb commands:

(gdb) bt
(gdb) info reg
(gdb) disas $pc-16*8 $pc+16*4

回答4:

Most of these issues are caused by multiple upstream dependencies linking to different versions of the same library.

For example, both the gnustl and stlport provide distinct implementations of the C++ standard library. If you compile and link against gnustl, while one of your dependencies was compiled and linked against stlport, then you will each have a different implementation of standard functions and classes. When your program is launched, the dynamic linker will attempt to resolve all of the exported symbols, and will discover known symbols at incorrect offsets, resulting in the BUS_ADRALN signal.