[Qemu-devel] [PATCH] linux-user: Fixed brk syscall memory allocation

[Qemu-devel] [PATCH] linux-user: Fixed brk syscall memory allocation

[Stanislav Shmarov]

When application is trying to allocate memory through brk
QEMU is allocating host memory using mmap.
Without MAP_FIXED attribute it is possible that memory will
never be allocated in desired place, and brk syscall will
act like there is no avalible memory.

Signed-off-by: Stanislav Shmarov <snarpix@gmail.com>
---
 linux-user/syscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ca06943..2861db2 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -1030,7 +1030,8 @@ abi_long do_brk(abi_ulong new_brk)
     new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
     mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
                                         PROT_READ|PROT_WRITE,
-                                        MAP_ANON|MAP_PRIVATE, 0, 0));
+                                        MAP_ANON | MAP_PRIVATE | MAP_FIXED,
+                                        0, 0));
 
     if (mapped_addr == brk_page) {
         /* Heap contents are initialized to zero, as for anonymous
-- 
1.9.3

Re: [Qemu-devel] [PATCH] linux-user: Fixed brk syscall memory allocation

[Stanislav Shmarov]

Please ignore this patch. Issue was in another place, and proposed solution
is simply wrong.

2016-09-13 16:14 GMT+03:00 Stanislav Shmarov <snarpix@gmail.com>:

> When application is trying to allocate memory through brk
> QEMU is allocating host memory using mmap.
> Without MAP_FIXED attribute it is possible that memory will
> never be allocated in desired place, and brk syscall will
> act like there is no avalible memory.
>
> Signed-off-by: Stanislav Shmarov <snarpix@gmail.com>
> ---
>  linux-user/syscall.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index ca06943..2861db2 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -1030,7 +1030,8 @@ abi_long do_brk(abi_ulong new_brk)
>      new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
>      mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
>                                          PROT_READ|PROT_WRITE,
> -                                        MAP_ANON|MAP_PRIVATE, 0, 0));
> +                                        MAP_ANON | MAP_PRIVATE |
> MAP_FIXED,
> +                                        0, 0));
>
>      if (mapped_addr == brk_page) {
>          /* Heap contents are initialized to zero, as for anonymous
> --
> 1.9.3
>
>