[Qemu-devel] playing with qemu usermode emulation on FreeBSD...

[Juergen Lock]

I recently noticed there are x86 bsd-user targets now (yeah I totally
missed those commits...) and now got it working a tiny little bit:
I can run
        qemu-x86_64 -bsd freebsd /rescue/echo foo bar
here on FreeBSD 8/amd64 and it echoes foo bar as expected, but
segfaults afterwards. :)  (in pthread_setcancelstate() invoked from
a guest write() syscall, in case anyone is wondering.)  Other things
I tried either exit with errors or segfault as well, and i386 hosts
probably still don't work at all yet.  (qemu-i386 here on amd64 does
at least something, but probably needs lock_user() treatment for all
kinds of syscalls, I only tried adding that for sysctl so far.)

 Anyway, here is an emulators/qemu-devel git head snapshot port
update with my current patches (files/patch-bsd-user), feel free to
test/debug/improve:
        http://people.freebsd.org/~nox/qemu/qemu-devel-20091007.patch
(For the folks reading this on the qemu list:  I shall start doing
`proper' patch submissions later, this is more for the FreeBSD folks
and because I was asked to send what I have...)

 Enjoy,
        Juergen

PS: well I guess I could inline the patch here too so the curious
don't have to extract it out of the update:

Index: qemu/bsd-user/freebsd/strace.list
@@ -39,6 +39,7 @@
 { TARGET_FREEBSD_NR_ftruncate, "ftruncate", NULL, NULL, NULL },
 { TARGET_FREEBSD_NR_futimes, "futimes", NULL, NULL, NULL },
 { TARGET_FREEBSD_NR_getdirentries, "getdirentries", NULL, NULL, NULL },
+{ TARGET_FREEBSD_NR_freebsd6_mmap, "freebsd6_mmap", NULL, NULL, NULL },
 { TARGET_FREEBSD_NR_getegid, "getegid", "%s()", NULL, NULL },
 { TARGET_FREEBSD_NR_geteuid, "geteuid", "%s()", NULL, NULL },
 { TARGET_FREEBSD_NR_getfh, "getfh", NULL, NULL, NULL },
Index: qemu/bsd-user/elfload.c
@@ -126,6 +126,8 @@
     regs->rax = 0;
     regs->rsp = infop->start_stack;
     regs->rip = infop->entry;
+    if (1 /* bsd_type == target_freebsd */)
+        regs->rdi = infop->start_stack;
 }
 
 #else
Index: qemu/bsd-user/main.c
@@ -171,26 +171,63 @@
         switch(trapnr) {
         case 0x80:
             /* syscall from int $0x80 */
-            env->regs[R_EAX] = do_openbsd_syscall(env,
-                                                  env->regs[R_EAX],
-                                                  env->regs[R_EBX],
-                                                  env->regs[R_ECX],
-                                                  env->regs[R_EDX],
-                                                  env->regs[R_ESI],
-                                                  env->regs[R_EDI],
-                                                  env->regs[R_EBP]);
+            if (bsd_type == target_freebsd) {
+                abi_ulong params = (abi_ulong) env->regs[R_ESP] +
+                    sizeof(int32_t);
+                abi_ulong arg1, arg2, arg3, arg4, arg5, arg6;
+
+                get_user_s32(arg1, params);
+                params += sizeof(int32_t);
+                get_user_s32(arg2, params);
+                params += sizeof(int32_t);
+                get_user_s32(arg3, params);
+                params += sizeof(int32_t);
+                get_user_s32(arg4, params);
+                params += sizeof(int32_t);
+                get_user_s32(arg5, params);
+                params += sizeof(int32_t);
+                get_user_s32(arg6, params);
+                env->regs[R_EAX] = do_freebsd_syscall(env,
+                                                      env->regs[R_EAX],
+                                                      arg1,
+                                                      arg2,
+                                                      arg3,
+                                                      arg4,
+                                                      arg5,
+                                                      arg6);
+            } else { //if (bsd_type == target_openbsd)
+                env->regs[R_EAX] = do_openbsd_syscall(env,
+                                                      env->regs[R_EAX],
+                                                      env->regs[R_EBX],
+                                                      env->regs[R_ECX],
+                                                      env->regs[R_EDX],
+                                                      env->regs[R_ESI],
+                                                      env->regs[R_EDI],
+                                                      env->regs[R_EBP]);
+            }
             break;
 #ifndef TARGET_ABI32
         case EXCP_SYSCALL:
             /* linux syscall from syscall intruction */
-            env->regs[R_EAX] = do_openbsd_syscall(env,
-                                                  env->regs[R_EAX],
-                                                  env->regs[R_EDI],
-                                                  env->regs[R_ESI],
-                                                  env->regs[R_EDX],
-                                                  env->regs[10],
-                                                  env->regs[8],
-                                                  env->regs[9]);
+            if (bsd_type == target_freebsd)
+                env->regs[R_EAX] = do_freebsd_syscall(env,
+                                                      env->regs[R_EAX],
+                                                      env->regs[R_EDI],
+                                                      env->regs[R_ESI],
+                                                      env->regs[R_EDX],
+                                                      env->regs[10],
+                                                      env->regs[8],
+                                                      env->regs[9]);
+            else { //if (bsd_type == target_openbsd)
+                env->regs[R_EAX] = do_openbsd_syscall(env,
+                                                      env->regs[R_EAX],
+                                                      env->regs[R_EDI],
+                                                      env->regs[R_ESI],
+                                                      env->regs[R_EDX],
+                                                      env->regs[10],
+                                                      env->regs[8],
+                                                      env->regs[9]);
+            }
             env->eip = env->exception_next_eip;
             break;
 #endif
Index: qemu/bsd-user/syscall.c
@@ -29,6 +29,7 @@
 #include <sys/types.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
+#include <sys/sysctl.h>
 #include <signal.h>
 #include <utime.h>
 
@@ -40,14 +41,88 @@
 static abi_ulong target_brk;
 static abi_ulong target_original_brk;
 
-#define get_errno(x) (x)
+static inline abi_long get_errno(abi_long ret)
+{
+    if (ret == -1)
+        /* XXX need to translate host -> target errnos here */
+        return -(errno);
+    else
+        return ret;
+}
+
 #define target_to_host_bitmask(x, tbl) (x)
 
+static inline int is_error(abi_long ret)
+{
+    return (abi_ulong)ret >= (abi_ulong)(-4096);
+}
+
 void target_set_brk(abi_ulong new_brk)
 {
     target_original_brk = target_brk = HOST_PAGE_ALIGN(new_brk);
 }
 
+/* do_obreak() must return target errnos. */
+static abi_long do_obreak(abi_ulong new_brk)
+{
+    abi_ulong brk_page;
+    abi_long mapped_addr;
+    int new_alloc_size;
+
+    if (!new_brk)
+        return 0;
+    if (new_brk < target_original_brk)
+        return -TARGET_EINVAL;
+
+    brk_page = HOST_PAGE_ALIGN(target_brk);
+
+    /* If the new brk is less than this, set it and we're done... */
+    if (new_brk < brk_page) {
+        target_brk = new_brk;
+        return 0;
+    }
+
+    /* We need to allocate more memory after the brk... */
+    new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page + 1);
+    mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
+                                        PROT_READ|PROT_WRITE,
+                                        MAP_ANON|MAP_FIXED|MAP_PRIVATE, -1, 
0));
+
+    if (!is_error(mapped_addr))
+        target_brk = new_brk;
+    else
+        return mapped_addr;
+
+    return 0;
+}
+
+/* XXX this needs to be emulated on non-FreeBSD hosts... */
+static abi_long do_freebsd_sysctl(abi_ulong namep, int32_t namelen, abi_ulong 
oldp,
+                          abi_ulong oldlenp, abi_ulong newp, abi_ulong newlen)
+{
+    abi_long ret;
+    void *hnamep, *holdp, *hnewp = NULL;
+    size_t holdlen;
+    abi_ulong oldlen = 0;
+
+    if (oldlenp)
+        get_user_ual(oldlen, oldlenp);
+    if (!(hnamep = lock_user(VERIFY_READ, namep, namelen, 1)))
+        return -TARGET_EFAULT;
+    if (newp && !(hnewp = lock_user(VERIFY_READ, newp, newlen, 1)))
+        return -TARGET_EFAULT;
+    if (!(holdp = lock_user(VERIFY_WRITE, oldp, oldlen, 0)))
+        return -TARGET_EFAULT;
+    holdlen = oldlen;
+    ret = get_errno(sysctl(hnamep, namelen, holdp, &holdlen, hnewp, newlen));
+    put_user_ual(holdlen, oldlenp);
+    unlock_user(hnamep, namep, 0);
+    unlock_user(holdp, oldp, holdlen);
+    if (hnewp)
+        unlock_user(hnewp, newp, 0);
+    return ret;
+}
+
 /* do_syscall() should always have a single exit point at the end so
    that actions, such as logging of syscall results, can be performed.
    All errnos that do_syscall() returns must be -TARGET_<errcode>. */
@@ -103,12 +178,18 @@
     case TARGET_FREEBSD_NR_mprotect:
         ret = get_errno(target_mprotect(arg1, arg2, arg3));
         break;
+    case TARGET_FREEBSD_NR_break:
+        ret = do_obreak(arg1);
+        break;
+    case TARGET_FREEBSD_NR___sysctl:
+        ret = do_freebsd_sysctl(arg1, arg2, arg3, arg4, arg5, arg6);
+        break;
     case TARGET_FREEBSD_NR_syscall:
     case TARGET_FREEBSD_NR___syscall:
         ret = do_freebsd_syscall(cpu_env,arg1 & 
0xffff,arg2,arg3,arg4,arg5,arg6,0);
         break;
     default:
-        ret = syscall(num, arg1, arg2, arg3, arg4, arg5, arg6);
+        ret = get_errno(syscall(num, arg1, arg2, arg3, arg4, arg5, arg6));
         break;
     }
  fail:
Index: qemu/cpu-exec.c
@@ -1252,6 +1252,12 @@
 # define TRAP_sig(context)    ((context)->sc_trapno)
 # define ERROR_sig(context)   ((context)->sc_err)
 # define MASK_sig(context)    ((context)->sc_mask)
+#elif defined(__FreeBSD__)
+#include <sys/ucontext.h>
+#define EIP_sig(context)      ((context)->uc_mcontext.mc_eip)
+#define TRAP_sig(context)     ((context)->uc_mcontext.mc_trapno)
+#define ERROR_sig(context)    ((context)->uc_mcontext.mc_err)
+#define MASK_sig(context)     ((context)->uc_sigmask)
 #else
 # define EIP_sig(context)     ((context)->uc_mcontext.gregs[REG_EIP])
 # define TRAP_sig(context)    ((context)->uc_mcontext.gregs[REG_TRAPNO])
@@ -1265,6 +1271,8 @@
     siginfo_t *info = pinfo;
 #if defined(__OpenBSD__)
     struct sigcontext *uc = puc;
+#elif defined(__FreeBSD__)
+    ucontext_t *uc = puc;
 #else
     struct ucontext *uc = puc;
 #endif
@@ -1297,6 +1305,12 @@
 #define TRAP_sig(context)     ((context)->sc_trapno)
 #define ERROR_sig(context)    ((context)->sc_err)
 #define MASK_sig(context)     ((context)->sc_mask)
+#elif defined(__FreeBSD__)
+#include <sys/ucontext.h>
+#define PC_sig(context)       ((context)->uc_mcontext.mc_rip)
+#define TRAP_sig(context)     ((context)->uc_mcontext.mc_trapno)
+#define ERROR_sig(context)    ((context)->uc_mcontext.mc_err)
+#define MASK_sig(context)     ((context)->uc_sigmask)
 #else
 #define PC_sig(context)       ((context)->uc_mcontext.gregs[REG_RIP])
 #define TRAP_sig(context)     ((context)->uc_mcontext.gregs[REG_TRAPNO])
@@ -1313,6 +1327,8 @@
     ucontext_t *uc = puc;
 #elif defined(__OpenBSD__)
     struct sigcontext *uc = puc;
+#elif defined(__FreeBSD__)
+    ucontext_t *uc = puc;
 #else
     struct ucontext *uc = puc;
 #endif