This patch makes thumb2_breakpoint static. When writing this patch,
I find the only reason we keep thumb2_breakpoint extern is that it
is used as an argument passed to arm_gdbserver_get_next_pcs. However,
field arm_thumb2_breakpoint is only used in a null check in
thumb_get_next_pcs_raw, so I wonder why do need to pass thumb2_breakpoint
to arm_gdbserver_get_next_pcs.
thumb2_breakpoint was added by Daniel Jacobowitz in order to support
single-step IT block
https://sourceware.org/ml/gdb-patches/2010-01/msg00624.html the logic
there was if we have 32-bit thumb-2 breakpoint defined, we can safely
single-step IT block, otherwise, we can't. Daniel didn't want to use
16-bit thumb BKPT instruction, because it triggers even on instruction
which should be executed. Secondly, using 16-bit thumb illegal
instruction on top of 32-bit thumb instruction may break the meaning of
original IT blocks, because the other 16-bit can be regarded as an
instruction. See more explanations from Daniel's kernel patch
http://www.spinics.net/lists/arm-kernel/msg80476.html
Let us back to this patch, GDB/GDBserver can safely single step
IT block if thumb2_breakpoint is defined, but the single step logic
doesn't have to know the thumb-2 breakpoint instruction. Only
breakpoint insertion mechanism decides to use which breakpoint
instruction. In the software single step code, instead of pass
thumb2_breakpoint, we can pass a boolean variable
has_thumb2_breakpoint indicate whether the target has thumb-2
breakpoint defined, which is equivalent to the original code.
Regression tested on arm-linux. No regression.
gdb:
2016-01-14 Yao Qi <yao.qi@linaro.org>
* arch/arm-get-next-pcs.c (arm_get_next_pcs_ctor): Change
argument arm_thumb2_breakpoint to has_thumb2_breakpoint.
(thumb_get_next_pcs_raw): Check has_thumb2_breakpoint
instead.
* arch/arm-get-next-pcs.h (struct arm_get_next_pcs)
<arm_thumb2_breakpoint>: Remove.
<has_thumb2_breakpoint>: New field.
(arm_get_next_pcs_ctor): Update declaration.
* arm-linux-tdep.c (arm_linux_software_single_step): Pass
1 to arm_get_next_pcs_ctor.
* arm-tdep.c (arm_software_single_step): Pass 0 to
arm_get_next_pcs_ctor.
gdb/gdbserver:
2016-01-14 Yao Qi <yao.qi@linaro.org>
* linux-aarch32-low.c (thumb2_breakpoint): Make it static.
* linux-aarch32-low.h (thumb2_breakpoint): Remove declaration.
* linux-arm-low.c (arm_gdbserver_get_next_pcs): Pass 1 to
arm_get_next_pcs_ctor.
1b451dda5f