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+Title: Dillo 3.1.0: Freeze on Nav_open_url in Cygwin
+Author: Isles487
+Created: Sun, 19 May 2024 18:06:47 +0000
+State: closed
+
+In updated Cygwin, using 3.1.0 release of Dillo, I am encountering process freezes when attempting to open Urls:
+
+Windows 11, 64 bit
+Cygwin64 terminal
+VcXsrv 1.20.14.0
+
+Console:
+
+$ DISPLAY=:0.0 dillo
+paths: Cannot open file '/home/someuser/.dillo/dillorc': No such file or directory
+paths: Using /usr/local/etc/dillo/dillorc
+paths: Cannot open file '/home/someuser/.dillo/keysrc': No such file or directory
+paths: Using /usr/local/etc/dillo/keysrc
+paths: Cannot open file '/home/someuser/.dillo/domainrc': No such file or directory
+paths: Using /usr/local/etc/dillo/domainrc
+Domain: Default accept.
+dillo_dns_init: Here we go! (threaded)
+TLS library: OpenSSL 3.0.13 30 Jan 2024
+Disabling cookies.
+paths: Cannot open file '/home/someuser/.dillo/hsts_preload': No such file or directory
+paths: Using /usr/local/etc/dillo/hsts_preload
+Nav_open_url: new url='about:splash'
+Nav_open_url: new url='https://dillo-browser.github.io/'
+Dns_server [0]: dillo-browser.github.io is 185.199.108.153 185.199.110.153 185.199.109.153 185.199.111.153
+Connecting to 185.199.108.153:443
+dillo-browser.github.io: TLSv1.3, cipher TLS_AES_128_GCM_SHA256
+sha256 2048-bit RSA: /C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=*.github.io
+sha256 2048-bit RSA: /C=US/O=DigiCert Inc/CN=DigiCert Global G2 TLS RSA SHA256 2020 CA1
+root: /C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert Global Root G2
+Nav_open_url: new url='https://www.fltk.org/'
+
+At this point the application becomes unresponsive and I need to kill via Task Manager.
+
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 18:19:35 +0000
+
+Does it also happen with Xorg? https://github.com/dillo-browser/dillo/blob/master/doc/install.md#windows-via-cygwin
+
+--%--
+From: Isles487
+Date: Sun, 19 May 2024 18:22:01 +0000
+
+> Does it also happen with Xorg? https://github.com/dillo-browser/dillo/blob/master/doc/install.md#windows-via-cygwin
+
+Yes it does, same issue after using startxwin and then connecting to the X server via a different cygwin terminal window.
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 19:06:04 +0000
+
+> Yes it does, same issue after using startxwin and then connecting to the X server via a different cygwin terminal window.
+
+I cannot reproduce it when using mbedTLS 2.23.0, I will try with OpenSSL too.
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 19:17:50 +0000
+
+I can reproduce it with OpenSSL 3.0.13. I will take a look and see if I can find the problem, thanks for reporting.
+
+In the meanwhile, you can install mbedTLS (mbedtls-devel) and configure Dillo with `--disable-openssl` so it uses it instead of OpenSSL, which seems to be working fine.
+
+--%--
+From: Isles487
+Date: Sun, 19 May 2024 19:19:54 +0000
+
+> I can reproduce it with OpenSSL 3.0.13. I will take a look and see if I can find the problem, thanks for reporting.
+> 
+> In the meanwhile, you can install mbedTLS (mbedtls-devel) and configure Dillo with `--disable-openssl` so it uses it instead of OpenSSL, which seems to be working fine.
+
+Thank you for looking into this and confirming! 
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 19:40:47 +0000
+
+There seems to be a problem which only occurs with OpenSSL and when the threaded DNS resolver is enabled.
+
+When building with OpenSSL, you can disable the threaded DNS resolver by configuring Dillo with `--disable-threaded-dns`. That seems to be working fine too.
+
+I cannot see where the problem is coming from, as the stack seems corrupted from GDB:
+```
+...
+[New Thread 3376.0x3e0]
+[New Thread 3376.0x1b60]
+[New Thread 3376.0x223c]
+[New Thread 3376.0x2b50]
+Nav_open_url: new url='about:splash'
+[New Thread 3376.0x2e58]
+Nav_open_url: new url='https://dillo-browser.github.io/'
+[New Thread 3376.0x5ec]
+Dns_server [0]: dillo-browser.github.io is 185.199.109.153 185.199.110.153 185.199.108.153 185.199.111.153
+
+Thread 11 "dillo" received signal SIGSEGV, Segmentation fault.
+[Switching to Thread 3376.0x5ec]
+0x0000000000000000 in ?? ()
+(gdb) bt
+#0  0x0000000000000000 in ?? ()
+#1  0x00007ffdcc659a03 in cygwin1!.getreent () from /usr/bin/cygwin1.dll
+#2  0x00007ffdcc73a3bb in timegm () from /usr/bin/cygwin1.dll
+#3  0x000000007ffe0385 in ?? ()
+Backtrace stopped: previous frame inner to this frame (corrupt stack?)
+```
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 20:11:29 +0000
+
+So, I took a look and what seems to be happening is that after a thread is spawned to resolve a host, the thread finishes and exits by returning NULL. The control is returned to cygwin, at which point the `rbp` (the base of the stack) is set to zero:
+
+```
+(gdb) p $rbp
+$12 = (void *) 0x0
+```
+
+Causing a SEGFAULT in the next push instruction.
+
+I'm not sure if this is a problem on Cygwin or on Dillo side. I cannot enable Asan on Cygwin, as it doesn't seem to be supported. With the stack protector enabled, there is no warning of any kind.
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 20:23:05 +0000
+
+Here is the bug, the thread has overwritten the stored rbp register in the stack with 0, causing the `pop %rbp`  instruction to set the value of rbp to zero.
+
+![image](https://github.com/dillo-browser/dillo/assets/3866127/03ceaa54-8465-4a17-9089-706ddbcdf5c1)
+
+I just need to see what is causing it, probably an stack overflow.
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 20:56:42 +0000
+
+Well, it seems the rbp register is not the problem, as it enters the Dns_server function with value zero. The problem seems to be the [detached state](https://github.com/dillo-browser/dillo/blob/ea2263231abc770d5d87fcdb95fddd80679c5906/src/dns.c#L356):
+
+```
+pthread_attr_setdetachstate(&thrATTR, PTHREAD_CREATE_DETACHED);
+```
+
+When that line is removed, the thread works fine. But when it is set, the alloca call done by cywgin after the thread finishes is failing. This starts to look like a bug in Cygwin.
+
+As a workaround, disabling DNS threads seems to be the best solution for now.
+
+--%--
+From: Isles487
+Date: Sun, 19 May 2024 20:58:58 +0000
+
+> Well, it seems the rbp register is not the problem, as it enters the Dns_server function with value zero. The problem seems to be the [detached state](https://github.com/dillo-browser/dillo/blob/ea2263231abc770d5d87fcdb95fddd80679c5906/src/dns.c#L356):
+> 
+> ```
+> pthread_attr_setdetachstate(&thrATTR, PTHREAD_CREATE_DETACHED);
+> ```
+> 
+> When that line is removed, the thread works fine. But when it is set, the alloca call done by cywgin after the thread finishes is failing. This starts to look like a bug in Cygwin.
+> 
+> As a workaround, disabling DNS threads seems to be the best solution for now.
+
+I don't know if this information is useful in determining whether Cygwin is the issue or not, but interestingly when I compile the links2 browser: http://links.twibright.com/, I need to run with -async-dns disabled otherwise the browser crashes after loading more than one page - also using same openssl.
+
+--%--
+From: rodarima
+Date: Sun, 19 May 2024 21:15:00 +0000
+
+Here is a reproducer which causes a SEGFAULT with OpenSSL only:
+
+```
+$ cat p.c
+#include <pthread.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#include <openssl/ssl.h>
+
+#define N 4
+
+static void *foo(void *data)
+{
+        printf("hello th %d\n", (int) data);
+        return NULL;
+}
+
+int main()
+{
+        SSL_library_init();
+        pthread_t th[N];
+        pthread_attr_t attr;
+        pthread_attr_init(&attr);
+        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+
+        for (int i = 0; i < N; i++)
+                pthread_create(&th[i], &attr, foo, (void *) i);
+
+        sleep(5);
+}
+
+$ gcc p.c -lssl -pthread -o p
+
+$ gdb ./p
+GNU gdb (GDB) (Cygwin 13.2-1) 13.2
+Copyright (C) 2023 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.
+Type "show copying" and "show warranty" for details.
+This GDB was configured as "x86_64-pc-cygwin".
+Type "show configuration" for configuration details.
+For bug reporting instructions, please see:
+<https://www.gnu.org/software/gdb/bugs/>.
+Find the GDB manual and other documentation resources online at:
+    <http://www.gnu.org/software/gdb/documentation/>.
+
+For help, type "help".
+Type "apropos word" to search for commands related to "word"...
+Reading symbols from ./p...
+(gdb) r
+Starting program: /home/PC/dillo/build-openssl/p
+[New Thread 7332.0x1f2c]
+[New Thread 7332.0x99c]
+[New Thread 7332.0x27d4]
+[New Thread 7332.0x35e0]
+[New Thread 7332.0x21dc]
+[New Thread 7332.0x3170]
+[New Thread 7332.0x1ea4]
+[New Thread 7332.0x3180]
+hello th 0
+hello th 1
+hello th 2
+[Thread 7332.0x3170 exited with code 0]
+hello th 3
+
+Thread 6 "p" received signal SIGSEGV, Segmentation fault.
+[Switching to Thread 7332.0x21dc]
+0x0000000000000000 in ?? ()
+```
+
+This is likely a bug in Cygwin triggered by OpenSSL, so I will report it to them. In the meanwhile I will modify the documentation for Windows to disable the threaded DNS resolver,
+
+--%--
+From: rodarima
+Date: Mon, 20 May 2024 18:32:47 +0000
+
+Confirmed: https://cygwin.com/pipermail/cygwin/2024-May/255975.html
+
+--%--
+From: Isles487
+Date: Mon, 20 May 2024 19:23:55 +0000
+
+Thank you again for looking into this so quickly and keeping me updated on this! Appreciate your work. Let me know if appropriate to close now.
+
+--%--
+From: rodarima
+Date: Mon, 20 May 2024 19:28:12 +0000
+
+> Thank you again for looking into this so quickly and keeping me updated on this! Appreciate your work. Let me know if appropriate to close now.
+
+Don't worry, it will be closed automatically when I merge https://github.com/dillo-browser/dillo/pull/173 :-)
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