RE: Infinite Stack Unwinding ARM

[Johannes Stoelp <Johannes dot Stoelp at synopsys dot com>]

Yao Qi <qiyaoltc@gmail.com> writes:

> I don't expect prologue analyzer supporting SYSRegs and instruction MRS.  All the prologue analyzers in GDB are written in a way that understanding instructions according to the ABI/calling convention of each architecture and  compiler's behavior, so it should be able to parse the instruction in prologues complying to the ABI.  GDB prologue analyzer may not understand what does handwritten assembly do.


Hi Yao,

I see what you are saying about the prologue analyzer and the ABI/calling conventions. 

I understand that gdb does not have to understand every hand written assembler routine, but I would like to emphasize that gdb in this particular case ends in an "infinite" loop printing the backtrace line by line (I put infinite in quotes because the loop is limited by the lower boundary of an integer). 
I would expect gdb to be more defensive in this case and either try other unwinding techniques like backward unwinding (from bottom up) or just stop unwinding because of to less information.
In my understanding situations like this can also occur when the stack gets corrupted. There I would also expect gdb to not end in an infinite loop since gdb is intended to analyze the non-expected situation.

One other question that came up by comparing the arm and the aarch64 analyzer:
    * Is there a special reason/trick why the arm analyzer (gdb/arm-tdep.c:arm_analyze_prologue(...)) skips instructions that it doesn't recognize while the aarch64 analyzer (gdb/aarch64-tdep.c:aarch64_prologue_analyzer(...)) stops when the first unrecognized instruction is hit?

Best,
Johannes