[Qemu-arm] recvfrom error with linux-user emulating armhf on aarch64

["Guido Günther" <agx@sigxcpu.org>]

[-- Attachment #1: Type: text/plain, Size: 1596 bytes --]

Hi,
Running the attached program⁰ in a armhf chroot on a arm64 host¹ like:

    chroot . /usr/bin/qemu-arm-static tmp/nl-bad-addr

fails with "Bad address" when invoking audit_log_acct_message. strace looks like:

  [..snip..]
  31572 socket(AF_NETLINK, SOCK_RAW, NETLINK_AUDIT) = 3
  ...
  31572 sendto(3, {{len=124, type=0x454 /* NLMSG_??? */, flags=NLM_F_REQUEST|NLM_F_ACK, seq=1, pid=0}, "op=test:message acct=\"?\" exe=\"/tmp/nl-bad-addr\" hostname=localhost addr=? terminal=/dev/pts/2 res=success\0\0\0"}, 124, 0, 0xfffffa3897d0, 0) = 124
  31572 ppoll([{fd=3, events=POLLIN}], 1, {tv_sec=0, tv_nsec=500000000}, NULL, 0) = 1 ([{fd=3, revents=POLLIN}], left {tv_sec=0, tv_nsec=499993180})
  31572 recvfrom(3, 0x112a50eb4, 8988, MSG_PEEK|MSG_DONTWAIT, 0xfffffa3897e0, 0x42) = -1 EFAULT (Bad address)
  [..snip..]

And it fails in

   ret = get_errno(safe_recvfrom(fd, host_msg, len, flags,
                                      addr, &addrlen));

in linux-user/syscall.c:do_recvfrom but I have no idea yet what causes this.

However the same works without problems when the host is a x86_64 box.
Any pointers in debugging this further would be appreciated.

The issue is also present in qemu master. The overall goal is to get

   qemu-debootstrap --arch armhf buster chroot

to succeed on an aarch64 host as it does on x86_64.
Cheers,
 -- Guido

P.S.: Please cc: me on replies since I'm currently not subscribed to qemu-arm.

⁹: which is a stripped down testcase for /usr/bin/chfn failing
¹: the scaleway server this runs on doesn't support armhf.

[-- Attachment #2: audit.c --]
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// gcc -Wall -O2 audit.c -laudit

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#include <libaudit.h>


void err(const char* str)
{
  fprintf(stderr, "%s\n", str);
  exit(1);
}

int main()
{
  int audit_fd, rc;
  audit_fd = audit_open();

  if (audit_fd < 0)
      err("audit_open");
    
  rc = audit_log_acct_message (audit_fd, AUDIT_USER_CHAUTHTOK, NULL, "test:message",
                              "?", -1, "localhost", NULL, "/dev/pts/2", 1);
  if (rc < 0)
     err("audit_log_acct_message");

  audit_close(audit_fd);
  return 0;
}