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For GNU/Linux on x86-64, if the target is using the xsave format for passing the floating-point information from the inferior then there currently exists a bug relating to the x87 control registers, and the mxcsr register. The xsave format allows different floating-point features to be lazily enabled, a bit in the xsave format tells GDB which floating-point features have been enabled, and which have not. Currently in GDB, when reading the floating point state, we check the xsave bit flags, if the feature is enabled then we read the feature from the xsave buffer, and if the feature is not enabled, then we supply the default value from within GDB. Within GDB, when writing the floating point state, we first fetch the xsave state from the target and then, for any feature that is not yet enabled, we write the default values into the xsave buffer. Next we compare the regcache value with the value in the xsave buffer, and, if the value has changed we update the value in the xsave buffer, and mark the feature enabled in the xsave bit flags. The problem then, is that the x87 control registers were not following this pattern. We assumed that these registers were always written out by the kernel, and we always wrote them out to the xsave buffer (but didn't enabled the feature). The result of this is that if the kernel had not yet enabled the x87 feature then within GDB we would see random values for the x87 floating point control registers, and if the user tried to modify one of these register, that modification would be lost. Finally, the mxcsr register was also broken in the same way as the x87 control registers. The added complexity with this case is that the mxcsr register is part of both the avx and sse floating point feature set. When reading or writing this register we need to check that at least one of these features is enabled. This bug was present in native GDB, and within gdbserver. Both are fixed with this commit. gdb/ChangeLog: * common/x86-xstate.h (I387_FCTRL_INIT_VAL): New constant. (I387_MXCSR_INIT_VAL): New constant. * amd64-tdep.c (amd64_supply_xsave): Only read state from xsave buffer if it was supplied by the inferior. * i387-tdep.c (i387_supply_fsave): Use I387_MXCSR_INIT_VAL. (i387_xsave_get_clear_bv): New function. (i387_supply_xsave): Only read x87 control registers from the xsave buffer if the feature is enabled, and the state will have been written, otherwise, provide a suitable default. (i387_collect_xsave): Pre-clear all registers in xsave buffer, including x87 control registers. Update control registers if they have changed from the default value, and mark features as enabled as required. * i387-tdep.h (i387_xsave_get_clear_bv): Declare. gdb/gdbserver/ChangeLog: * i387-fp.c (i387_cache_to_xsave): Only write x87 control registers to the cache if their values have changed. (i387_xsave_to_cache): Provide default values for x87 control registers when these features are available, but disabled. * regcache.c (supply_register_by_name_zeroed): New function. * regcache.h (supply_register_by_name_zeroed): Declare new function. gdb/testsuite/ChangeLog: * gdb.arch/amd64-init-x87-values.S: New file. * gdb.arch/amd64-init-x87-values.exp: New file.
123 lines
3.9 KiB
C
123 lines
3.9 KiB
C
/* Register support routines for the remote server for GDB.
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Copyright (C) 2001-2018 Free Software Foundation, Inc.
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This file is part of GDB.
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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 as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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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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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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#ifndef REGCACHE_H
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#define REGCACHE_H
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#include "common-regcache.h"
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struct thread_info;
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struct target_desc;
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/* The data for the register cache. Note that we have one per
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inferior; this is primarily for simplicity, as the performance
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benefit is minimal. */
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struct regcache
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{
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/* The regcache's target description. */
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const struct target_desc *tdesc;
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/* Whether the REGISTERS buffer's contents are valid. If false, we
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haven't fetched the registers from the target yet. Not that this
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register cache is _not_ pass-through, unlike GDB's. Note that
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"valid" here is unrelated to whether the registers are available
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in a traceframe. For that, check REGISTER_STATUS below. */
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int registers_valid;
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int registers_owned;
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unsigned char *registers;
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#ifndef IN_PROCESS_AGENT
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/* One of REG_UNAVAILBLE or REG_VALID. */
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unsigned char *register_status;
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#endif
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};
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struct regcache *init_register_cache (struct regcache *regcache,
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const struct target_desc *tdesc,
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unsigned char *regbuf);
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void regcache_cpy (struct regcache *dst, struct regcache *src);
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/* Create a new register cache for INFERIOR. */
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struct regcache *new_register_cache (const struct target_desc *tdesc);
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struct regcache *get_thread_regcache (struct thread_info *thread, int fetch);
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/* Release all memory associated with the register cache for INFERIOR. */
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void free_register_cache (struct regcache *regcache);
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/* Invalidate cached registers for one thread. */
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void regcache_invalidate_thread (struct thread_info *);
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/* Invalidate cached registers for all threads of the given process. */
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void regcache_invalidate_pid (int pid);
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/* Invalidate cached registers for all threads of the current
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process. */
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void regcache_invalidate (void);
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/* Invalidate and release the register cache of all threads of the
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current process. */
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void regcache_release (void);
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/* Convert all registers to a string in the currently specified remote
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format. */
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void registers_to_string (struct regcache *regcache, char *buf);
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/* Convert a string to register values and fill our register cache. */
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void registers_from_string (struct regcache *regcache, char *buf);
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/* For regcache_read_pc see common/common-regcache.h. */
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void regcache_write_pc (struct regcache *regcache, CORE_ADDR pc);
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int register_cache_size (const struct target_desc *tdesc);
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int register_size (const struct target_desc *tdesc, int n);
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int find_regno (const struct target_desc *tdesc, const char *name);
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void supply_register (struct regcache *regcache, int n, const void *buf);
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void supply_register_zeroed (struct regcache *regcache, int n);
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void supply_register_by_name (struct regcache *regcache,
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const char *name, const void *buf);
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void supply_register_by_name_zeroed (struct regcache *regcache,
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const char *name);
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void supply_regblock (struct regcache *regcache, const void *buf);
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void collect_register (struct regcache *regcache, int n, void *buf);
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void collect_register_as_string (struct regcache *regcache, int n, char *buf);
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void collect_register_by_name (struct regcache *regcache,
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const char *name, void *buf);
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#endif /* REGCACHE_H */
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