Re: [Bug 1895080] [NEW] pgb_reserved_va: Assertion `addr == test' failed

[Alex Bennée]

Laurent Vivier <laurent@vivier.eu> writes:

> Le 10/09/2020 à 07:21, Launchpad Bug Tracker a écrit :
>> This problem occurs on CentOS-7.5 (64-bit) with qemu-5.1.0, qemu head
>> (commit 9435a8b3dd35f1f926f1b9127e8a906217a5518a) for riscv32-linux-
>> user.
>
> I tried to build qemu-5.1 on CentOS-7.5.1 but as python 3.5 is not
> available, I gave up.
>
>> Firstly, compile fails:
>> Compiling C object libqemu-riscv32-linux-user.fa.p/linux-user_strace.c.o
>> ../qemu.git/linux-user/strace.c:1210:18: error: ‘FALLOC_FL_KEEP_SIZE’ 
>> undeclared here (not in a function)
>>      FLAG_GENERIC(FALLOC_FL_KEEP_SIZE),
>> 
>> I have to add below include to linux-user/strace.c
>> diff --git a/linux-user/strace.c b/linux-user/strace.c
>> index 11fea14fba..22e51d4a8a 100644
>> --- a/linux-user/strace.c
>> +++ b/linux-user/strace.c
>> @@ -7,6 +7,7 @@
>>  #include <sys/mount.h>
>>  #include <arpa/inet.h>
>>  #include <netinet/tcp.h>
>> +#include <linux/falloc.h>
>>  #include <linux/if_packet.h>
>>  #include <linux/netlink.h>
>>  #include <sched.h>
>
> In fact, fallocate(2) says fcntl.h must be included.
> And qemu/osdep.h includes it.
> So you should not have this problem.
>
>> 
>> Then trying qemu-riscv32 with a simple ELF, I get:
>> linux-user/elfload.c:2341: pgb_reserved_va: Assertion `addr == test' failed.
>> 
>> strace shows that:
>> mmap(0x1000, 4294963200, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, 
>> -1, 0) = 0x10000
>> write(2, "qemu-riscv32: ../qemu.git/linux-"..., 103qemu-riscv32: 
>> ../qemu.git/linux-user/elfload.c:2341: pgb_reserved_va: Assertion `addr == 
>> test' failed.
>> ) = 103
>> 
>> The source code is in the function pgb_reserved_va (linux-
>> user/elfload.c). I think mmap cannot guarantee that the returned pointer
>> (test) equals to the parameter of addr. So is this a bug to assert (addr
>> == test)?
>
> I think Alex Bennée knows better this code than I do, so cc'ing him.

It should be able to do so because the earlier code (pgb_static) checks
for a hole the size of reserved_va in the host memory map. This should
be fairly easy for 32 bit guests given the amount of spare address space
you have on a 64 bit system.

I'm assuming CentOS 7.5 actually has a definition for
MAP_FIXED_NOREPLACE which should ensure we get what we asked for -
otherwise we are in the position of hoping the kernel honours what we
asked for.

>
> Thnaks
> Laurent


-- 
Alex Bennée

-- 
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https://bugs.launchpad.net/bugs/1895080

Title:
  pgb_reserved_va: Assertion `addr == test' failed

Status in QEMU:
  New

Bug description:
  This problem occurs on CentOS-7.5 (64-bit) with qemu-5.1.0, qemu head
  (commit 9435a8b3dd35f1f926f1b9127e8a906217a5518a) for riscv32-linux-
  user.

  Firstly, compile fails:
  Compiling C object libqemu-riscv32-linux-user.fa.p/linux-user_strace.c.o
  ../qemu.git/linux-user/strace.c:1210:18: error: ‘FALLOC_FL_KEEP_SIZE’ 
undeclared here (not in a function)
       FLAG_GENERIC(FALLOC_FL_KEEP_SIZE),

  I have to add below include to linux-user/strace.c
  diff --git a/linux-user/strace.c b/linux-user/strace.c
  index 11fea14fba..22e51d4a8a 100644
  --- a/linux-user/strace.c
  +++ b/linux-user/strace.c
  @@ -7,6 +7,7 @@
   #include <sys/mount.h>
   #include <arpa/inet.h>
   #include <netinet/tcp.h>
  +#include <linux/falloc.h>
   #include <linux/if_packet.h>
   #include <linux/netlink.h>
   #include <sched.h>

  Then trying qemu-riscv32 with a simple ELF, I get:
  linux-user/elfload.c:2341: pgb_reserved_va: Assertion `addr == test' failed.

  strace shows that:
  mmap(0x1000, 4294963200, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, 
-1, 0) = 0x10000
  write(2, "qemu-riscv32: ../qemu.git/linux-"..., 103qemu-riscv32: 
../qemu.git/linux-user/elfload.c:2341: pgb_reserved_va: Assertion `addr == 
test' failed.
  ) = 103

  The source code is in the function pgb_reserved_va (linux-
  user/elfload.c). I think mmap cannot guarantee that the returned
  pointer (test) equals to the parameter of addr. So is this a bug to
  assert (addr == test)?

  Attached configure script and test ELF file.

  Thanks.

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