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fddbd7c0ef
setcontext returns to the specified context via an indirect jump, so there should be a BTI j. In case of getcontext (and all other returns_twice functions) the compiler adds BTI j at the call site, but swapcontext is a normal c call that is currently not handled specially by the compiler. So we change swapcontext such that the saved context returns to a local address that has BTI j and then swapcontext returns to the caller via a normal RET. For this we save the original return address in the slot for x1 of the context because x1 need not be preserved by swapcontext but it is restored when the context saved by swapcontext is resumed. The alternative fix (which is done on x86) would make swapcontext special in the compiler so BTI j is emitted at call sites, on x86 there is an indirect_return attribute for this, on AArch64 we would have to use returns_twice. It was decided against because such fix may need user code updates: the attribute has to be added when swapcontext is called via a function pointer and it breaks always_inline functions with swapcontext. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
112 lines
3.1 KiB
ArmAsm
112 lines
3.1 KiB
ArmAsm
/* Modify saved context.
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Copyright (C) 2009-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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The GNU C Library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include "ucontext_i.h"
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#include "ucontext-internal.h"
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/* int swapcontext (ucontext_t *oucp, const ucontext_t *ucp) */
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.text
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ENTRY(__swapcontext)
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DELOUSE (0)
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/* Set the value returned when swapcontext() returns in this context.
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And set up x1 to become the return address of the caller, so we
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can return there with a normal RET instead of an indirect jump. */
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stp xzr, x30, [x0, oX0 + 0 * SZREG]
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/* Arrange the oucp context to return to 2f. */
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adr x30, 2f
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stp x18, x19, [x0, oX0 + 18 * SZREG]
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stp x20, x21, [x0, oX0 + 20 * SZREG]
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stp x22, x23, [x0, oX0 + 22 * SZREG]
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stp x24, x25, [x0, oX0 + 24 * SZREG]
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stp x26, x27, [x0, oX0 + 26 * SZREG]
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stp x28, x29, [x0, oX0 + 28 * SZREG]
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str x30, [x0, oX0 + 30 * SZREG]
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str x30, [x0, oPC]
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mov x2, sp
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str x2, [x0, oSP]
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/* Figure out where to place the first context extension
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block. */
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add x2, x0, #oEXTENSION
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/* Write the context extension fpsimd header. */
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mov w3, #(FPSIMD_MAGIC & 0xffff)
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movk w3, #(FPSIMD_MAGIC >> 16), lsl #16
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str w3, [x2, #oHEAD + oMAGIC]
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mov w3, #FPSIMD_CONTEXT_SIZE
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str w3, [x2, #oHEAD + oSIZE]
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/* Fill in the FP SIMD context. */
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add x3, x2, #oV0 + 8 * SZVREG
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stp q8, q9, [x3], #2 * SZVREG
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stp q10, q11, [x3], #2 * SZVREG
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stp q12, q13, [x3], #2 * SZVREG
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stp q14, q15, [x3], #2 * SZVREG
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add x3, x2, #oFPSR
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mrs x4, fpsr
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str w4, [x3, #oFPSR - oFPSR]
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mrs x4, fpcr
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str w4, [x3, #oFPCR - oFPSR]
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/* Write the termination context extension header. */
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add x2, x2, #FPSIMD_CONTEXT_SIZE
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str xzr, [x2, #oHEAD + oMAGIC]
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str xzr, [x2, #oHEAD + oSIZE]
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/* Preserve ucp. */
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mov x21, x1
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/* rt_sigprocmask (SIG_SETMASK, &ucp->uc_sigmask, &oucp->uc_sigmask,
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_NSIG8) */
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/* Grab the signal mask */
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/* rt_sigprocmask (SIG_BLOCK, NULL, &ucp->uc_sigmask, _NSIG8) */
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add x2, x0, #UCONTEXT_SIGMASK
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mov x0, SIG_BLOCK
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mov x1, 0
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mov x3, _NSIG8
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mov x8, SYS_ify (rt_sigprocmask)
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svc 0
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cbnz x0, 1f
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mov x22, x30
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mov x0, x21
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bl JUMPTARGET (__setcontext)
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mov x30, x22
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RET
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1:
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b C_SYMBOL_NAME(__syscall_error)
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2:
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/* The oucp context is restored here via an indirect branch,
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x1 must be restored too which has the real return address. */
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BTI_J
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mov x30, x1
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RET
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PSEUDO_END (__swapcontext)
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weak_alias (__swapcontext, swapcontext)
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