2 files changed, 83 insertions, 0 deletions
diff --git a/glibc/debugging/ld_so_console.mdwn b/glibc/debugging/ld_so_console.mdwn
new file mode 100644
index 00000000..b3d1762f
--- /dev/null
+++ b/glibc/debugging/ld_so_console.mdwn
@@ -0,0 +1,20 @@
+[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]]
+
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
+
+If you need to debug something in the early `ld.so` startup, and can't refrain
+from good old `printf` debugging, there is a caveat: the available API in
+`ld.so` is rather limited.  See the few functions is `dl-sysdep.c`.  For
+example, there's a private `__libc_write`, which you should be able to use for
+writing to FD stderr -- but, at early `ld.so` startup, this isn't usable as
+`_hurd_init_dtable` is still all zeros, etc.  To get you started, here is a
+simple [[dl-sysdep.c.patch]] to get access to the Mach console.
+
+Can this be integrated with the other debugging printf functions from
+`elf/dl-misc.c` (`_dl_debug_vdprintf`) ([[!taglink open_issue_glibc]])?
diff --git a/glibc/debugging/ld_so_console/dl-sysdep.c.patch b/glibc/debugging/ld_so_console/dl-sysdep.c.patch
new file mode 100644
index 00000000..eec8d7c6
--- /dev/null
+++ b/glibc/debugging/ld_so_console/dl-sysdep.c.patch
@@ -0,0 +1,63 @@
+diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
+index ff37add..7e6d352 100644
+--- a/sysdeps/mach/hurd/dl-sysdep.c
++++ b/sysdeps/mach/hurd/dl-sysdep.c
+@@ -44,6 +44,8 @@
+ #include <dl-machine.h>
+ #include <dl-procinfo.h>
+ 
++#include <device/device.h>
++
+ extern void __mach_init (void);
+ 
+ extern int _dl_argc;
+@@ -116,6 +118,29 @@ static void fmh(void) {
+ /* XXX loser kludge for vm_map kernel bug */
+ #endif
+ 
++/* Return a port to the Mach console.  */
++static mach_port_t
++get_console (void)
++{
++  mach_port_t device_master, console;
++  /* We cannot use __get_privileged_ports (from hurd/privports.c), as this
++     drags in too much other libc stuff.  */
++#if 0
++  error_t err = __get_privileged_ports (0, &device_master);
++
++  if (err)
++    return MACH_PORT_NULL;
++#else
++  error_t err = 0;
++  device_master = 2;
++#endif
++
++  err = __device_open (device_master, D_WRITE | D_READ, "console", &console);
++  if (err)
++    return MACH_PORT_NULL;
++
++  return console;
++}
+ 
+ ElfW(Addr)
+ _dl_sysdep_start (void **start_argptr,
+@@ -256,6 +279,20 @@ unfmh();			/* XXX */
+   /* Set up so we can do RPCs.  */
+   __mach_init ();
+ 
++  /* Open the Mach console so that any message can actually be seen.  This is
++     particularly useful at boot time, when started by the bootstrap file
++     system.  */
++  mach_port_t console = get_console ();
++  if (console != MACH_PORT_NULL)
++    {
++      /* stdout = mach_open_devstream (console, "w"); */
++      /* stderr = stdout; */
++      /* if (stdout != NULL) */
++      /* 	printf ("Hello, world!\n"); */
++      int written;
++      __device_write_inband (console, 0, 0, "hello, world!\n", 14, &written);
++    }
++
+   /* Initialize frequently used global variable.  */
+   GLRO(dl_pagesize) = __getpagesize ();
+\ No newline at end of file