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0d15ef6778
Current versions of gdb do not interoperate cleanly with kgdb on arm64
systems because gdb and kgdb do not use the same register description.
This patch modifies kgdb to work with recent releases of gdb (>= 7.8.1).
Compatibility with gdb (after the patch is applied) is as follows:
gdb-7.6 and earlier Ok
gdb-7.7 series Works if user provides custom target description
gdb-7.8(.0) Works if user provides custom target description
gdb-7.8.1 and later Ok
When commit 44679a4f14 ("arm64: KGDB: Add step debugging support") was
introduced it was paired with a gdb patch that made an incompatible
change to the gdbserver protocol. This patch was eventually merged into
the gdb sources:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=a4d9ba85ec5597a6a556afe26b712e878374b9dd
The change to the protocol was mostly made to simplify big-endian support
inside the kernel gdb stub. Unfortunately the gdb project released
gdb-7.7.x and gdb-7.8.0 before the protocol incompatibility was identified
and reversed:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=bdc144174bcb11e808b4e73089b850cf9620a7ee
This leaves us in a position where kgdb still uses the no-longer-used
protocol; gdb-7.8.1, which restored the original behaviour, was
released on 2014-10-29.
I don't believe it is possible to detect/correct the protocol
incompatiblity which means the kernel must take a view about which
version of the gdb remote protocol is "correct". This patch takes the
view that the original/current version of the protocol is correct
and that version found in gdb-7.7.x and gdb-7.8.0 is anomalous.
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
114 lines
3.8 KiB
C
114 lines
3.8 KiB
C
/*
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* AArch64 KGDB support
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*
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* Based on arch/arm/include/kgdb.h
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*
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* Copyright (C) 2013 Cavium Inc.
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* Author: Vijaya Kumar K <vijaya.kumar@caviumnetworks.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef __ARM_KGDB_H
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#define __ARM_KGDB_H
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#include <linux/ptrace.h>
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#include <asm/debug-monitors.h>
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#ifndef __ASSEMBLY__
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static inline void arch_kgdb_breakpoint(void)
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{
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asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM));
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}
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extern void kgdb_handle_bus_error(void);
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extern int kgdb_fault_expected;
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#endif /* !__ASSEMBLY__ */
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/*
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* gdb remote procotol (well most versions of it) expects the following
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* register layout.
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*
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* General purpose regs:
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* r0-r30: 64 bit
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* sp,pc : 64 bit
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* pstate : 32 bit
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* Total: 33 + 1
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* FPU regs:
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* f0-f31: 128 bit
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* fpsr & fpcr: 32 bit
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* Total: 32 + 2
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*
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* To expand a little on the "most versions of it"... when the gdb remote
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* protocol for AArch64 was developed it depended on a statement in the
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* Architecture Reference Manual that claimed "SPSR_ELx is a 32-bit register".
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* and, as a result, allocated only 32-bits for the PSTATE in the remote
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* protocol. In fact this statement is still present in ARM DDI 0487A.i.
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*
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* Unfortunately "is a 32-bit register" has a very special meaning for
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* system registers. It means that "the upper bits, bits[63:32], are
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* RES0.". RES0 is heavily used in the ARM architecture documents as a
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* way to leave space for future architecture changes. So to translate a
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* little for people who don't spend their spare time reading ARM architecture
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* manuals, what "is a 32-bit register" actually means in this context is
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* "is a 64-bit register but one with no meaning allocated to any of the
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* upper 32-bits... *yet*".
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*
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* Perhaps then we should not be surprised that this has led to some
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* confusion. Specifically a patch, influenced by the above translation,
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* that extended PSTATE to 64-bit was accepted into gdb-7.7 but the patch
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* was reverted in gdb-7.8.1 and all later releases, when this was
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* discovered to be an undocumented protocol change.
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*
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* So... it is *not* wrong for us to only allocate 32-bits to PSTATE
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* here even though the kernel itself allocates 64-bits for the same
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* state. That is because this bit of code tells the kernel how the gdb
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* remote protocol (well most versions of it) describes the register state.
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*
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* Note that if you are using one of the versions of gdb that supports
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* the gdb-7.7 version of the protocol you cannot use kgdb directly
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* without providing a custom register description (gdb can load new
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* protocol descriptions at runtime).
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*/
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#define _GP_REGS 33
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#define _FP_REGS 32
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#define _EXTRA_REGS 3
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/*
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* general purpose registers size in bytes.
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* pstate is only 4 bytes. subtract 4 bytes
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*/
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#define GP_REG_BYTES (_GP_REGS * 8)
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#define DBG_MAX_REG_NUM (_GP_REGS + _FP_REGS + _EXTRA_REGS)
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/*
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* Size of I/O buffer for gdb packet.
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* considering to hold all register contents, size is set
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*/
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#define BUFMAX 2048
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/*
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* Number of bytes required for gdb_regs buffer.
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* _GP_REGS: 8 bytes, _FP_REGS: 16 bytes and _EXTRA_REGS: 4 bytes each
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* GDB fails to connect for size beyond this with error
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* "'g' packet reply is too long"
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*/
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#define NUMREGBYTES ((_GP_REGS * 8) + (_FP_REGS * 16) + \
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(_EXTRA_REGS * 4))
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#endif /* __ASM_KGDB_H */
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