gdb stops with too many watchpoints when there is only one

Question

Do you know any other reasons why a watchpoint could not be inserted other than too many hardware breakpoints/watchpoints?

I have the following debug session:

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Answer 1

As far as I know commodity x86 CPUs have four debug registers available for supporting hardware breaks/watches. This limits the object size that you can watch. Object alignment also plays here.

Try limiting the watch scope to a smaller object like pair of first and last members of the structure.