On Fri, 2010-09-10 at 00:10 +0530, Uma shankar wrote: > Hi, > > I am trying to understand a particular program-crash i am looking > at now, coming from libpthread.so library in ARM. I am using > NPTL and glibc 4.2.1 > > >From stack-trace , i figured that pthread_self() is being called. > > >From source, I saw that this calls __builtin_thread_pointer(). This > function has been synthesized in gcc-source by a macro. > > The assembly of the function __builtin_thread_pointer() ( from > objdump of lib ) looks like > > mvn r0, 0xF000 > sub pc, r0, 0x1F8 > > This does not make sense. I thought of the possibility thagt > maybe this is a address-value which gets relocated, but this is > text-region of a shared library ( libpthread) and so is not relocated. > > I have 2 questions - > a) What is the meaning of the above asm code ? > b) As the program branches to invalid address 0xE8 somewhere after > pthread_self( ), what could be wrong ? > > I guess this is some kind of TLS-data corruption. > I would be reading about TLS in ARM tomorrow. > > Thanks The code is jumping to a 'well-known' address exported by the linux kernel. That address contains a processor-specific sequence of instructions that will return the TLS base for the current address. Of course, if you're not running on top of the Linux kernel, then you'll need to find another way of making all that work. If your CPU is based on ARMv7-A then the compiler will (should) use a CP-15 register directly as it's more efficient (but that register did not exist on earlier cores). R.
