[PATCH 2/2] linux-user/nios2: Map a real kuser page

[Richard Henderson]

The first word of page1 is data, so the whole thing
can't be implemented with emulation of addresses.

Hijack trap number 31 to implement cmpxchg.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c        | 35 +++++++++++++++++++++++++
 linux-user/nios2/cpu_loop.c | 52 ++++++++++++++++++++-----------------
 target/nios2/translate.c    |  9 -------
 3 files changed, 63 insertions(+), 33 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 01e9a833fb..e78c0af183 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1091,6 +1091,41 @@ static void elf_core_copy_regs(target_elf_gregset_t 
*regs, const CPUMBState *env
 
 static void init_thread(struct target_pt_regs *regs, struct image_info *infop)
 {
+    static const uint8_t kuser_page[128] = {
+        /* __kuser_helper_version */
+        [0x00] = 0x02, 0x00, 0x00, 0x00,
+
+        /* __kuser_cmpxchg */
+        [0x04] = 0xfa, 0x6f, 0x3b, 0x00,  /* trap 31 */
+                 0x3a, 0x28, 0x00, 0xf8,  /* ret */
+
+        /* __kuser_sigtramp */
+        [0x40] = 0xc4, 0x22, 0x80, 0x00,  /* movi r2, __NR_rt_sigreturn */
+                 0x3a, 0x68, 0x3b, 0x00,  /* trap 0 */
+    };
+
+    abi_ulong pg;
+    uint8_t *ph;
+
+    pg = target_mmap(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE,
+                     PROT_READ | PROT_WRITE,
+                     MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+
+    /*
+     * If the mmap doesn't give us exactly page 1, there's nothing
+     * we can do, and it's unlikely that the program will be able
+     * to continue.  FIXME: Error out now?
+     */
+    if (pg == TARGET_PAGE_SIZE) {
+        ph = lock_user(VERIFY_WRITE, pg, sizeof(kuser_page), 0);
+        memcpy(ph, kuser_page, sizeof(kuser_page));
+        unlock_user(ph, pg, sizeof(kuser_page));
+        target_mprotect(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE,
+                        PROT_READ | PROT_EXEC);
+    } else {
+        target_munmap(pg, TARGET_PAGE_SIZE);
+    }
+
     regs->ea = infop->entry;
     regs->sp = infop->start_stack;
     regs->estatus = 0x3;
diff --git a/linux-user/nios2/cpu_loop.c b/linux-user/nios2/cpu_loop.c
index d76bdb2891..fd3f853ac2 100644
--- a/linux-user/nios2/cpu_loop.c
+++ b/linux-user/nios2/cpu_loop.c
@@ -20,11 +20,11 @@
 #include "qemu/osdep.h"
 #include "qemu.h"
 #include "cpu_loop-common.h"
+#include "signal-common.h"
 
 void cpu_loop(CPUNios2State *env)
 {
     CPUState *cs = env_cpu(env);
-    Nios2CPU *cpu = NIOS2_CPU(cs);
     target_siginfo_t info;
     int trapnr, ret;
 
@@ -71,6 +71,32 @@ void cpu_loop(CPUNios2State *env)
                 force_sig_fault(TARGET_SIGILL, TARGET_ILL_ILLTRP,
                                 env->regs[R_PC]);
                 break;
+
+            case 31: /* QEMU specific, for __kuser_cmpxchg */
+                {
+                    abi_ptr g = env->regs[4];
+                    uint32_t *h, n, o;
+
+                    if (g & 0x3) {
+                        force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN, g);
+                        break;
+                    }
+                    ret = page_get_flags(g);
+                    if (!(ret & PAGE_VALID)) {
+                        force_sig_fault(TARGET_SIGSEGV, TARGET_SEGV_MAPERR, g);
+                        break;
+                    }
+                    if (!(ret & PAGE_READ) || !(ret & PAGE_WRITE)) {
+                        force_sig_fault(TARGET_SIGSEGV, TARGET_SEGV_ACCERR, g);
+                        break;
+                    }
+                    h = g2h(cs, g);
+                    o = env->regs[5];
+                    n = env->regs[6];
+                    env->regs[2] = qatomic_cmpxchg(h, o, n) - o;
+                    env->regs[R_PC] += 4;
+                }
+                break;
             }
             break;
 
@@ -81,29 +107,7 @@ void cpu_loop(CPUNios2State *env)
             queue_signal(env, info.si_signo, QEMU_SI_FAULT, &info);
             break;
         case 0xaa:
-            switch (env->regs[R_PC]) {
-            /*case 0x1000:*/  /* TODO:__kuser_helper_version */
-            case 0x1004:      /* __kuser_cmpxchg */
-                start_exclusive();
-                if (env->regs[4] & 0x3) {
-                    goto kuser_fail;
-                }
-                ret = get_user_u32(env->regs[2], env->regs[4]);
-                if (ret) {
-                    end_exclusive();
-                    goto kuser_fail;
-                }
-                env->regs[2] -= env->regs[5];
-                if (env->regs[2] == 0) {
-                    put_user_u32(env->regs[6], env->regs[4]);
-                }
-                end_exclusive();
-                env->regs[R_PC] = env->regs[R_RA];
-                break;
-            /*case 0x1040:*/  /* TODO:__kuser_sigtramp */
-            default:
-                ;
-kuser_fail:
+            {
                 info.si_signo = TARGET_SIGSEGV;
                 info.si_errno = 0;
                 /* TODO: check env->error_code */
diff --git a/target/nios2/translate.c b/target/nios2/translate.c
index 485b487665..77706dd805 100644
--- a/target/nios2/translate.c
+++ b/target/nios2/translate.c
@@ -795,15 +795,6 @@ static void nios2_tr_translate_insn(DisasContextBase 
*dcbase, CPUState *cs)
     dc->base.pc_next = pc + 4;
 
     /* Decode an instruction */
-
-#if defined(CONFIG_USER_ONLY)
-    /* FIXME: Is this needed ? */
-    if (pc >= 0x1000 && pc < 0x2000) {
-        t_gen_helper_raise_exception(dc, 0xaa);
-        return;
-    }
-#endif
-
     code = cpu_ldl_code(env, pc);
     op = get_opcode(code);
 
-- 
2.25.1