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Signal handlers are not direct function pointers but pointers to function descriptor in that case. Therefore we must retrieve the actual function address and load the GOT value into r9 from the descriptor before branching to the actual handler. If a restorer is provided, we also have to load its address and GOT from its descriptor. That descriptor address and the code to load it is pushed onto the stack to be executed as soon as the signal handler returns. However, to be compatible with NX stacks, the FDPIC bounce code is also copied to the signal page along with the other code stubs. Therefore this code must get at the descriptor address whether it executes from the stack or the signal page. To do so we use the stack pointer which points at the signal stack frame where the descriptor address was stored. Because the rt signal frame is different from the simpler frame, two versions of the bounce code are needed, and two variants (ARM and Thumb) as well. The asm-offsets facility is used to determine the actual offset in the signal frame for each version, meaning that struct sigframe and rt_sigframe had to be moved to a separate file. Signed-off-by: Nicolas Pitre <nico@linaro.org> Acked-by: Mickael GUENE <mickael.guene@st.com> Tested-by: Vincent Abriou <vincent.abriou@st.com> Tested-by: Andras Szemzo <szemzo.andras@gmail.com> |
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