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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>
68 lines
2.6 KiB
C
68 lines
2.6 KiB
C
/* Target description related code for GNU/Linux x86-64.
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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/amd64-linux-tdesc.h"
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#include "arch/amd64.h"
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#include "arch/x86-linux-tdesc-features.h"
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/* See arch/amd64-linux-tdesc.h. */
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const struct target_desc *
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amd64_linux_read_description (uint64_t xstate_bv, bool is_x32)
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{
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/* The type used for the amd64 and x32 target description caches. */
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using tdesc_cache_type = std::unordered_map<uint64_t, const target_desc_up>;
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/* Caches for the previously seen amd64 and x32 target descriptions,
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indexed by the xstate_bv value that created the target
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description. These need to be static within this function to ensure
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they are initialised before first use. */
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static tdesc_cache_type amd64_tdesc_cache, x32_tdesc_cache;
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tdesc_cache_type &tdesc_cache = is_x32 ? x32_tdesc_cache : amd64_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
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relevant for tdesc creation.
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When indexing into the TDESC_CACHE we need to use a consistent
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xstate_bv value otherwise we might fail to find an existing
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tdesc which has the same set of relevant bits set. */
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xstate_bv &= is_x32
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? x86_linux_x32_xstate_bv_feature_mask ()
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: x86_linux_amd64_xstate_bv_feature_mask ();
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const auto it = tdesc_cache.find (xstate_bv);
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if (it != 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 (amd64_create_target_description (xstate_bv, is_x32,
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true, true));
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x86_linux_post_init_tdesc (tdesc.get (), true);
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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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tdesc_cache.emplace (xstate_bv, std::move (tdesc));
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return ptr;
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}
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