[PowerPC] Add support for EBB and PMU registers

[PowerPC] Add support for EBB and PMU registers

This patch adds support for registers of the Event Based Branching and
Performance Monitoring Units for the powerpc linux native and core
file targets, and for the powerpc linux server stub.

All three EBB registers are accessible.  Only a subset of the PMU
registers can be accessed through ptrace.  Because of this, the PMU
registers are enumerated individually in gdbarch_tdep, as opposed to
having a single "have_pmu" flag.  This is intended to make it easier
to add additional PMU registers in the future, since checking a
"have_pmu" flag elsewhere in the code would no longer be correct.  The
tdesc feature is named org.gnu.gdb.power.linux.pmu because of this.

It's unclear if it makes sense to save and restore these registers
across function calls, since some of them can be modified
asynchronously.  They are also not tracked in record-replay mode.

The kernel can return ENODATA when ptrace is used to get the EBB
registers, unless a linux performance event that uses EBB is open in
the inferior.  For this reason, the "fill" functions in the server
stub for the ebb register sets is not implemented.

Since gdbserver writes all registers in one go before resuming the
inferior, this error would not be detected at the time the user tries
to write to one of the registers on the client side, and gdbserver
would print out warnings every time it resumes the inferior when no
ebb performance event is opened, so there is currently no
straightforward way to handle this case.  This means the ebb registers
in the client-side regcache can become dirty when the user tries to
write to them, until the inferior is resumed and stopped again.

A related issue is that 'G' packets used to write to unrelated
registers will include bad data for the EBB registers if they are
unavailable, since no register status information is included in the
'G' packet.  This data won't be written to the inferior by the
gdbserver stub because the "fill" functions are not implemented, and
currently the gdbserver stub doesn't change the status of the
registers in its own regcache in response to 'G' packets.

Another limitation for the ebb registers is that traceframes don't
record if registers are available or not, so if these registers are
collected when a tracepoint is hit and the inferior has no ebb event
opened, the user will see zero values for all of them, instead of the
usual <unavailable>.

Because these registers are often unavailable, trying to store them
with target_store_registers with -1 for the regno argument (all
registers) would almost always fail, so they are ignored in this case.

gdb/ChangeLog:
2018-10-26  Edjunior Barbosa Machado  <emachado@linux.vnet.ibm.com>
	    Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* arch/ppc-linux-common.h (PPC_LINUX_SIZEOF_EBBREGSET)
	(PPC_LINUX_SIZEOF_PMUREGSET): Declare.
	* nat/ppc-linux.h (PPC_FEATURE2_EBB, NT_PPC_EBB, NT_PPC_PMU):
	Define if not already defined.
	* features/rs6000/power-ebb.xml: New file.
	* features/rs6000/power-linux-pmu.xml: New file.
	* features/rs6000/powerpc-isa207-vsx32l.xml: Include ebb and pmu
	features.
	* features/rs6000/powerpc-isa207-vsx64l.xml: Likewise.
	* features/rs6000/powerpc-isa207-vsx32l.c: Re-generate.
	* features/rs6000/powerpc-isa207-vsx64l.c: Re-generate.
	* regformats/rs6000/powerpc-isa207-vsx32l.dat: Re-generate.
	* regformats/rs6000/powerpc-isa207-vsx64l.dat: Re-generate.
	* ppc-linux-nat.c (fetch_register, fetch_ppc_registers): Call
	fetch_regset with ebb and pmu regsets.
	(store_register, store_ppc_registers): Call store_regset with ebb
	and pmu regsets.
	(ppc_linux_nat_target::read_description): Set isa207 field in the
	features struct if ebb and pmu are avaiable.
	* ppc-linux-tdep.c (ppc32_regmap_ebb, ppc32_regmap_pmu)
	(ppc32_linux_ebbregset, ppc32_linux_pmuregset): New globals.
	(ppc_linux_iterate_over_regset_sections): Call back with the ebb
	and pmu regsets.
	(ppc_linux_core_read_description): Check if the pmu section is
	present and set isa207 in the features struct.
	* ppc-linux-tdep.h (ppc32_linux_ebbregset)
	(ppc32_linux_pmuregset): Declare.
	* ppc-tdep.h (struct gdbarch_tdep) <ppc_mmcr0_regnum>: New field.
	<ppc_mmcr2_regnum, ppc_siar_regnum, ppc_sdar_regnum>: New fields.
	<ppc_sier_regnum>: New field.
	(enum): <PPC_BESCR_REGNUM, PPC_EBBHR_REGNUM, PPC_EBBRR_REGNUM>:
	New enum values.
	<PPC_MMCR0_REGNUM, PPC_MMCR2_REGNUM, PPC_SIAR_REGNUM>: New enum
	values.
	<PPC_SDAR_REGNUM, PPC_SIER_REGNUM>: New enum values.
	(PPC_IS_EBB_REGNUM, PPC_IS_PMU_REGNUM): Define.
	* rs6000-tdep.c (rs6000_gdbarch_init): Look for and validate the
	ebb and pmu features.

gdb/gdbserver/ChangeLog:
2018-10-26  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* configure.srv (powerpc*-*-linux*): Add rs6000/power-ebb.xml and
	rs6000/power-linux-pmu.xml to srv_xmlfiles.
	* linux-ppc-low.c (ppc_store_ebbregset, ppc_fill_pmuregset)
	(ppc_store_pmuregset): New functions.
	(ppc_regsets): Add entries for ebb and pmu regsets.
	(ppc_arch_setup): Set isa207 in features struct if the ebb and
	pmu regsets are available.  Set sizes for these regsets.

gdb/doc/ChangeLog:
2018-10-26  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* gdb.texinfo (PowerPC Features): Describe new features
	"org.gnu.gdb.power.ebb" and "org.gnu.gdb.power.linux.pmu".