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gdb, gdbserver: Use xstate_bv for target description creation on x86.

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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>
This commit is contained in:
Christina Schimpe
2024-12-03 08:32:10 -08:00
parent 92cc4fb226
commit 6ef3896cfe
22 changed files with 196 additions and 155 deletions
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4
gdbsupport/x86-xstate.h
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@@ -83,8 +83,10 @@ constexpr bool operator!= (const x86_xsave_layout &lhs,
#define X86_XSTATE_AVX_AVX512_PKU_MASK (X86_XSTATE_AVX_MASK\
| X86_XSTATE_AVX512 | X86_XSTATE_PKRU)
#define X86_XSTATE_ALL_MASK (X86_XSTATE_AVX_AVX512_PKU_MASK)
/* Supported mask of state-component bitmap xstate_bv. The SDM defines
xstate_bv as XCR0 | IA32_XSS. */
#define X86_XSTATE_ALL_MASK (X86_XSTATE_AVX_AVX512_PKU_MASK)
#define X86_XSTATE_SSE_SIZE 576
#define X86_XSTATE_AVX_SIZE 832