[Qemu-devel] [PATCH 2/7] QEMU does not currently support host pages that are larger than guest pages, likely due to glibc using fixed mmap requests.

[Timothy Pearson]

Attempting to use host pages larger than the guest leads to
alignment errors during ELF load in the best case, and an
initialization failure inside NPTL in the worst case, causing
all fork() requests inside the guest to fail.

Warn when thread space cannot be set up, and suggest reducing
host page size if applicable.

Signed-off-by: Timothy Pearson <address@hidden>
---
 linux-user/syscall.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 1c17b74..2968b57 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5482,8 +5482,13 @@ static int do_fork(CPUArchState *env, unsigned int 
flags, abi_ulong newsp,
             /* Wait for the child to initialize.  */
             pthread_cond_wait(&info.cond, &info.mutex);
             ret = info.tid;
-            if (flags & CLONE_PARENT_SETTID)
-                put_user_u32(ret, parent_tidptr);
+            if (flags & CLONE_PARENT_SETTID) {
+                if (put_user_u32(ret, parent_tidptr)) {
+                    fprintf(stderr, "do_fork: put_user_u32() failed, child 
process state invalid\n");
+                    if (qemu_real_host_page_size > TARGET_PAGE_SIZE)
+                        fprintf(stderr, "do_fork: host page size > target page 
size; reduce host page size and try again\n");
+                }
+            }
         } else {
             ret = -1;
         }
@@ -5514,10 +5519,20 @@ static int do_fork(CPUArchState *env, unsigned int 
flags, abi_ulong newsp,
                (not implemented) or having *_tidptr to point at a shared memory
                mapping.  We can't repeat the spinlock hack used above because
                the child process gets its own copy of the lock.  */
-            if (flags & CLONE_CHILD_SETTID)
-                put_user_u32(gettid(), child_tidptr);
-            if (flags & CLONE_PARENT_SETTID)
-                put_user_u32(gettid(), parent_tidptr);
+            if (flags & CLONE_CHILD_SETTID) {
+                if (put_user_u32(gettid(), child_tidptr)) {
+                    fprintf(stderr, "do_fork: put_user_u32() failed, child 
process state invalid\n");
+                    if (qemu_real_host_page_size > TARGET_PAGE_SIZE)
+                        fprintf(stderr, "do_fork: host page size > target page 
size; reduce host page size and try again\n");
+                }
+            }
+            if (flags & CLONE_PARENT_SETTID) {
+                if (put_user_u32(gettid(), parent_tidptr)) {
+                    fprintf(stderr, "do_fork: put_user_u32() failed, child 
process state invalid\n");
+                    if (qemu_real_host_page_size > TARGET_PAGE_SIZE)
+                        fprintf(stderr, "do_fork: host page size > target page 
size; reduce host page size and try again\n");
+                }
+            }
             ts = (TaskState *)cpu->opaque;
             if (flags & CLONE_SETTLS)
                 cpu_set_tls (env, newtls);
-- 
2.1.4