linux-user/nios2: Map a real kuser page

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

Hijack trap number 16 to implement cmpxchg.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211221025012.1057923-5-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

2 files changed, 76 insertions, 24 deletions

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index d34cd4fe43..329b2375ef 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1099,6 +1099,47 @@ static void init_thread(struct target_pt_regs *regs, struct image_info *infop)
     regs->estatus = 0x3;
 }
 
+#define LO_COMMPAGE  TARGET_PAGE_SIZE
+
+static bool init_guest_commpage(void)
+{
+    static const uint8_t kuser_page[4 + 2 * 64] = {
+        /* __kuser_helper_version */
+        [0x00] = 0x02, 0x00, 0x00, 0x00,
+
+        /* __kuser_cmpxchg */
+        [0x04] = 0x3a, 0x6c, 0x3b, 0x00,  /* trap 16 */
+                 0x3a, 0x28, 0x00, 0xf8,  /* ret */
+
+        /* __kuser_sigtramp */
+        [0x44] = 0xc4, 0x22, 0x80, 0x00,  /* movi r2, __NR_rt_sigreturn */
+                 0x3a, 0x68, 0x3b, 0x00,  /* trap 0 */
+    };
+
+    void *want = g2h_untagged(LO_COMMPAGE & -qemu_host_page_size);
+    void *addr = mmap(want, qemu_host_page_size, PROT_READ | PROT_WRITE,
+                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
+
+    if (addr == MAP_FAILED) {
+        perror("Allocating guest commpage");
+        exit(EXIT_FAILURE);
+    }
+    if (addr != want) {
+        return false;
+    }
+
+    memcpy(addr, kuser_page, sizeof(kuser_page));
+
+    if (mprotect(addr, qemu_host_page_size, PROT_READ)) {
+        perror("Protecting guest commpage");
+        exit(EXIT_FAILURE);
+    }
+
+    page_set_flags(LO_COMMPAGE, LO_COMMPAGE + TARGET_PAGE_SIZE,
+                   PAGE_READ | PAGE_EXEC | PAGE_VALID);
+    return true;
+}
+
 #define ELF_EXEC_PAGESIZE        4096
 
 #define USE_ELF_CORE_DUMP
@@ -2160,8 +2201,13 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
     return sp;
 }
 
-#ifndef HI_COMMPAGE
+#if defined(HI_COMMPAGE)
+#define LO_COMMPAGE 0
+#elif defined(LO_COMMPAGE)
+#define HI_COMMPAGE 0
+#else
 #define HI_COMMPAGE 0
+#define LO_COMMPAGE 0
 #define init_guest_commpage() true
 #endif
 
@@ -2374,6 +2420,8 @@ static void pgb_static(const char *image_name, abi_ulong orig_loaddr,
         } else {
             offset = -(HI_COMMPAGE & -align);
         }
+    } else if (LO_COMMPAGE) {
+        loaddr = MIN(loaddr, LO_COMMPAGE & -align);
     }
 
     addr = pgb_find_hole(loaddr, hiaddr - loaddr, align, offset);
diff --git a/linux-user/nios2/cpu_loop.c b/linux-user/nios2/cpu_loop.c
index 5c3d01d22d..de0fc63e21 100644
--- a/linux-user/nios2/cpu_loop.c
+++ b/linux-user/nios2/cpu_loop.c
@@ -76,6 +76,32 @@ void cpu_loop(CPUNios2State *env)
                 force_sig_fault(TARGET_SIGILL, TARGET_ILL_ILLTRP,
                                 env->regs[R_PC]);
                 break;
+
+            case 16: /* 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;
 
@@ -86,29 +112,7 @@ 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 */