Re: [HURD, PATCH] Fix stack switching at initialization time

[Thomas Schwinge]

Hi!

Is this beast ever going to die...

On Fri, 22 Jul 2011 17:53:12 +0200, ludo@gnu.org wrote:
> Pushed a slightly different version, thanks!
> 
> http://git.savannah.gnu.org/cgit/hurd/glibc.git/commit/?h=t/init-first.c&id=53b56b1101fc9bb4f295f23f54e7e19f8da8da16

Just a heads-up, and I'm afraid, but with this patch I get:

    $ ./testrun.sh ./libc.so
    Segmentation fault

Undoing it (see below), I'm back in service:

    $ ./testrun.sh ./libc.so
    GNU C Library development release version 2.11.90, by Roland McGrath et al.
    [...]

This is still based on 2010-04 glibc sources, GCC 4.4, and old binutils
2.20.1.

Perhaps it'd really be best to write this in a few lines of assembly?


Undo patch:

diff --git a/sysdeps/mach/hurd/i386/init-first.c 
b/sysdeps/mach/hurd/i386/init-first.c
index caf65bb..7d93638 100644
--- a/sysdeps/mach/hurd/i386/init-first.c
+++ b/sysdeps/mach/hurd/i386/init-first.c
@@ -257,8 +257,8 @@ init (int *data)
       /* Push the user code address on the top of the new stack.  It will
         be the return address for `init1'; we will jump there with NEWSP
         as the stack pointer.  */
-      *--newsp = __builtin_return_address (0);
-      * ((void **) __builtin_frame_address (0) + 1) = &switch_stacks;
+      *--newsp = data[-1];
+      data[-1] = (int) &switch_stacks;
       /* Force NEWSP into %eax and &init1 into %ecx, which are not restored
         by function return.  */
       asm volatile ("# a %0 c %1" : : "a" (newsp), "c" (&init1));
@@ -286,8 +286,8 @@ init (int *data)
 
       /* The argument data is just above the stack frame we will unwind by
         returning.  Mutate our own return address to run the code below.  */
-      usercode = __builtin_return_address (0);
-      * ((void **) __builtin_frame_address (0) + 1) = &call_init1;
+      usercode = data[-1];
+      data[-1] = (int) &call_init1;
       /* Force USERCODE into %eax and &init1 into %ecx, which are not
         restored by function return.  */
       asm volatile ("# a %0 c %1" : : "a" (usercode), "c" (&init1));


Grüße,
 Thomas

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