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

["Alex Bennée" <1895080@bugs.launchpad.net>]

Alex Bennée <alex.bennee@linaro.org> writes:

> Laurent Vivier <laurent@vivier.eu> writes:
>
<snip>
>>> 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'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.

Doh re-reading I see it's not set in the strace output. Maybe we should
promote the assert case to the failure leg so we have:

    if (addr == MAP_FAILED || addr != test) {
        error_report(...)
    }

so we at least fail with a user friendly error rather than an abort?

-- 
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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