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@@ -464,6 +464,55 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
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#endif
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return 0;
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+#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
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+ /*
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+ * Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
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+ * Return zero in r0 if *MEM was changed or non-zero if no exchange
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+ * happened. Also set the user C flag accordingly.
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+ * If access permissions have to be fixed up then non-zero is
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+ * returned and the operation has to be re-attempted.
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+ *
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+ * *NOTE*: This is a ghost syscall private to the kernel. Only the
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+ * __kuser_cmpxchg code in entry-armv.S should be aware of its
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+ * existence. Don't ever use this from user code.
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+ */
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+ case 0xfff0:
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+ {
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+ extern void do_DataAbort(unsigned long addr, unsigned int fsr,
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+ struct pt_regs *regs);
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+ unsigned long val;
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+ unsigned long addr = regs->ARM_r2;
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+ struct mm_struct *mm = current->mm;
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+ pgd_t *pgd; pmd_t *pmd; pte_t *pte;
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+
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+ regs->ARM_cpsr &= ~PSR_C_BIT;
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+ spin_lock(&mm->page_table_lock);
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+ pgd = pgd_offset(mm, addr);
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+ if (!pgd_present(*pgd))
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+ goto bad_access;
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+ pmd = pmd_offset(pgd, addr);
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+ if (!pmd_present(*pmd))
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+ goto bad_access;
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+ pte = pte_offset_map(pmd, addr);
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+ if (!pte_present(*pte) || !pte_write(*pte))
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+ goto bad_access;
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+ val = *(unsigned long *)addr;
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+ val -= regs->ARM_r0;
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+ if (val == 0) {
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+ *(unsigned long *)addr = regs->ARM_r1;
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+ regs->ARM_cpsr |= PSR_C_BIT;
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+ }
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+ spin_unlock(&mm->page_table_lock);
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+ return val;
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+
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+ bad_access:
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+ spin_unlock(&mm->page_table_lock);
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+ /* simulate a read access fault */
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+ do_DataAbort(addr, 15 + (1 << 11), regs);
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+ return -1;
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+ }
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+#endif
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+
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default:
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/* Calls 9f00xx..9f07ff are defined to return -ENOSYS
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if not implemented, rather than raising SIGILL. This
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Linus Torvalds