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The XSAVE function set is organized in state components, which are a set of registers or parts of registers. So-called XSAVE-supported features are organized using state-component bitmaps, each bit corresponding to a single state component. The Intel Software Developer's Manual uses the term xstate_bv for a state-component bitmap, which is defined as XCR0 | IA32_XSS. The control register XCR0 only contains a state-component bitmap that specifies user state components, while IA32_XSS contains a state-component bitmap that specifies supervisor state components. Until now, XCR0 is used as input for target description creation in GDB. However, a following patch will add userspace support for the CET shadow stack feature by Intel. The CET state is configured in IA32_XSS and consists of 2 state components: - State component 11 used for the 2 MSRs controlling user-mode functionality for CET (CET_U state) - State component 12 used for the 3 MSRs containing shadow-stack pointers for privilege levels 0-2 (CET_S state). Reading the CET shadow stack pointer register on linux requires a separate ptrace call using NT_X86_SHSTK. To pass the CET shadow stack enablement state we would like to pass the xstate_bv value instead of xcr0 for target description creation. To prepare for that, we rename the xcr0 mask values for target description creation to xstate_bv. However, this patch doesn't add any functional changes in GDB. Future states specified in IA32_XSS such as CET will create a combined xstate_bv_mask including xcr0 register value and its corresponding bit in the state component bitmap. This combined mask will then be used to create the target descriptions. Reviewed-By: Thiago Jung Bauermann <thiago.bauermann@linaro.org> Approved-By: Luis Machado <luis.machado@arm.com>
60 lines
2.3 KiB
C
60 lines
2.3 KiB
C
/* Target description related code for GNU/Linux i386.
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Copyright (C) 2024-2025 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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#include "arch/x86-linux-tdesc.h"
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#include "arch/i386-linux-tdesc.h"
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#include "arch/i386.h"
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#include "arch/x86-linux-tdesc-features.h"
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/* See arch/i386-linux-tdesc.h. */
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const target_desc *
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i386_linux_read_description (uint64_t xstate_bv)
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{
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/* Cache of previously seen i386 target descriptions, indexed by the
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xstate_bv value that created the target description. This
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needs to be static within this function to ensure it is initialised
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before first use. */
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static std::unordered_map<uint64_t, const target_desc_up> i386_tdesc_cache;
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/* Only some bits are checked when creating a tdesc, but the
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XSTATE_BV value contains other feature bits that are not relevant
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for tdesc creation. When indexing into the I386_TDESC_CACHE
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we need to use a consistent XSTATE_BV value otherwise we might fail
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to find an existing tdesc which has the same set of relevant bits
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set. */
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xstate_bv &= x86_linux_i386_xstate_bv_feature_mask ();
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const auto it = i386_tdesc_cache.find (xstate_bv);
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if (it != i386_tdesc_cache.end ())
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return it->second.get ();
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/* Create the previously unseen target description. */
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target_desc_up tdesc
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(i386_create_target_description (xstate_bv, true, false));
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x86_linux_post_init_tdesc (tdesc.get (), false);
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/* Add to the cache, and return a pointer borrowed from the
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target_desc_up. This is safe as the cache (and the pointers contained
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within it) are not deleted until GDB exits. */
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target_desc *ptr = tdesc.get ();
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i386_tdesc_cache.emplace (xstate_bv, std::move (tdesc));
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return ptr;
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}
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