Re: [Qemu-devel] [qemu-s390x] linux-user: s390x issue on Fedora 30 (dynamic library loader?)

[Aleksandar Markovic]

Hi, David.

I can't repro the problem either, but I do have a patch authored by an
engineer that left the company a while ago that seems to be at least
related to your scenario. May I ask you to test it (just apply it to QEMU
ToT and rerun the scenario to see if it changes the outcome) (feel free to
experiment and modify the changes)? I never managed to understand the
purpose of that patch (I lost the contact with the former engineer, and the
patch is without any comment), so I never dared to send it to the list, but
I hope your scenario may actually explain the purpose and the origin of the
patch.

I am attaching the patch both as a file and inline.

Yours,
Aleksandar


>From 377f99e807f4aa42ece9f0cd437f50af11611b4c Mon Sep 17 00:00:00 2001
From: Aleksandar Markovic <address@hidden>
Date: Mon, 19 Aug 2019 15:20:29 +0200
Subject: [PATCH] linux-user: Special case /etc/ld.cache.so and pretend it
does
 not exist

Prevent target executables from opening host ld.so.cache.
---
 linux-user/syscall.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8367cb1..f5bae6e 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8820,6 +8820,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(statfs(path(p), &stfs));
         unlock_user(p, arg1, 0);
     convert_statfs:
@@ -8859,6 +8863,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(statfs(path(p), &stfs));
         unlock_user(p, arg1, 0);
     convert_statfs64:
@@ -9059,6 +9067,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(stat(path(p), &st));
         unlock_user(p, arg1, 0);
         goto do_stat;
@@ -9068,6 +9080,10 @@ static abi_long do_syscall1(void *cpu_env, int num,
abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(lstat(path(p), &st));
         unlock_user(p, arg1, 0);
         goto do_stat;
@@ -10268,6 +10284,10 @@ static abi_long do_syscall1(void *cpu_env, int
num, abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(stat(path(p), &st));
         unlock_user(p, arg1, 0);
         if (!is_error(ret))
@@ -10279,6 +10299,10 @@ static abi_long do_syscall1(void *cpu_env, int
num, abi_long arg1,
         if (!(p = lock_user_string(arg1))) {
             return -TARGET_EFAULT;
         }
+        if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+            unlock_user(p, arg1, 0);
+            return -TARGET_ENONET;
+        }
         ret = get_errno(lstat(path(p), &st));
         unlock_user(p, arg1, 0);
         if (!is_error(ret))
@@ -10319,6 +10343,10 @@ static abi_long do_syscall1(void *cpu_env, int
num, abi_long arg1,
             if (p == NULL) {
                 return -TARGET_EFAULT;
             }
+            if (strcmp("/etc/ld.so.cache", path(p)) == 0) {
+                unlock_user(p, arg1, 0);
+                return -TARGET_ENONET;
+            }
 #if defined(__NR_statx)
             {
                 /*
-- 
2.7.4


On Mon, Aug 19, 2019 at 3:08 PM David Hildenbrand <address@hidden> wrote:

> On 19.08.19 14:11, Peter Maydell wrote:
> > On Sat, 17 Aug 2019 at 17:14, David Hildenbrand <address@hidden>
> wrote:
> >>
> >> On 17.08.19 17:59, David Hildenbrand wrote:
> >>> Hi everybody,
> >>>
> >>> I was just trying to run qemu-s390x (linux-user) with a very simple
> >>> binary (gzip + lib/ld64.so.1, compiled under Fedora 27). This used to
> >>> work just fine a while ago (especially when I was working on vector
> >>> instructions using QEMU v3.1). However, now I can't get past a SEGFAULT
> >>> in the dynamic library loader (I assume it is trying to locate glibc).
> I
> >>> tried a couple of other binaries that definitely used to work (from
> >>> Fedora 30).
> >>>
> >>> I checked QEMU v4.1, v4.0 and v3.1. All are broken for me. Which is
> >>> weird - because it used to work :/
> >>>
> >>> I remember that I was running Fedora 29 the last time I had it running,
> >>> so my gut feeling is that this is related to some other system library
> >>> (but which?). I am running on an up-to-date Fedora 30 x86-64 now.
> >>>
> >>> Any ideas? Has this been reported already? (not sure if this is a
> Fedora
> >>> 30 issue)
> >
> > I'm pretty sure the problem you've run into is a long standing
> > bug in the glibc dynamic loader. It cannot cope with the ld.so.cache
> > being for the wrong endianness. (Correct endianness but incorrect
> > architecture it correctly detects and ignores). The result is that
> > running a linux-user QEMU dynamic binary for big-endian on little-endian
> > like this will crash in the dynamic loader unless you arrange that it
> can't
> > find the host's ld.so.cache somehow, eg:
> >  (a) run inside a chroot
> >  (b) create an empty /etc/ld.so.cache file inside the -L directory
> >
> > The ideal fix would be if somebody cared enough to track down
> > and fix the ld.so bug.
> >
> > Compare:
> > https://bugs.launchpad.net/qemu/+bug/1701798
> > https://bugs.launchpad.net/qemu/+bug/1835693
> >
> > thanks
> > -- PMM
> >
>
> Thanks, running
>
> "ldconfig -c etc/ld.so.cache -r ."
>
> Seems to fix the issue for me. So you are sure the bug resides in glic
> and not in the qemu-user pieces of the library loader?
>
> --
>
> Thanks,
>
> David / dhildenb
>
>

0001-linux-user-Special-case-etc-ld.cache.so-and-pretend-.patch
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