bsd-user/arm/target_arch_thread.h: Routines to create and switch to a thread

Implement target_thread_init (to create a thread) and target_set_upcall
(to switch to a thread) for arm.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>

bsd-user/arm/target_arch_thread.h

+/*
+ *  arm thread support
+ *
+ *  Copyright (c) 2013 Stacey D. Son
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef _TARGET_ARCH_THREAD_H_
+#define _TARGET_ARCH_THREAD_H_
+
+/* Compare to arm/arm/vm_machdep.c cpu_set_upcall_kse() */
+static inline void target_thread_set_upcall(CPUARMState *env, abi_ulong entry,
+    abi_ulong arg, abi_ulong stack_base, abi_ulong stack_size)
+{
+    abi_ulong sp;
+
+    /*
+     * Make sure the stack is properly aligned.
+     * arm/include/param.h (STACKLIGN() macro)
+     */
+    sp = (u_int)(stack_base + stack_size) & ~0x7;
+
+    /* sp = stack base */
+    env->regs[13] = sp;
+    /* pc = start function entry */
+    env->regs[15] = entry & 0xfffffffe;
+    /* r0 = arg */
+    env->regs[0] = arg;
+    env->spsr = ARM_CPU_MODE_USR;
+    /*
+     * Thumb mode is encoded by the low bit in the entry point (since ARM can't
+     * execute at odd addresses). When it's set, set the Thumb bit (T) in the
+     * CPSR.
+     */
+    cpsr_write(env, (entry & 1) * CPSR_T, CPSR_T, CPSRWriteByInstr);
+}
+
+static inline void target_thread_init(struct target_pt_regs *regs,
+        struct image_info *infop)
+{
+    abi_long stack = infop->start_stack;
+    memset(regs, 0, sizeof(*regs));
+    regs->ARM_cpsr = ARM_CPU_MODE_USR;
+    /*
+     * Thumb mode is encoded by the low bit in the entry point (since ARM can't
+     * execute at odd addresses). When it's set, set the Thumb bit (T) in the
+     * CPSR.
+     */
+    if (infop->entry & 1) {
+        regs->ARM_cpsr |= CPSR_T;
+    }
+    regs->ARM_pc = infop->entry & 0xfffffffe;
+    regs->ARM_sp = stack;
+    if (bsd_type == target_freebsd) {
+        regs->ARM_lr = infop->entry & 0xfffffffe;
+    }
+    /*
+     * FreeBSD kernel passes the ps_strings pointer in r0. This is used by some
+     * programs to set status messages that we see in ps. bsd-user doesn't
+     * support that functionality, so it's ignored. When set to 0, FreeBSD's csu
+     * code ignores it. For the static case, r1 and r2 are effectively ignored
+     * by the csu __startup() routine. For the dynamic case, rtld saves r0 but
+     * generates r1 and r2 and passes them into the csu _startup.
+     *
+     * r0 ps_strings 0 passed since ps arg setting not supported
+     * r1 obj_main   ignored by _start(), so 0 passed
+     * r2 cleanup    generated by rtld or ignored by _start(), so 0 passed
+     */
+}
+
+#endif /* !_TARGET_ARCH_THREAD_H_ */