hurd: Rework sbrk

Making the brk start exactly at the end of the main application binary was
requiring to get it through the _end symbol, which does not work any more
with recent toolchains, and actually produces in libc.so a confusing
external _end symbol that produces odd results, see
https://sourceware.org/bugzilla/show_bug.cgi?id=23499

Trying to do so is quite outdated anyway with the tendency for address
randomization.

Using _end was also allowing to include the main binary data within
the RLIMIT_DATA, but this also seems outdated with dynamic library
loading, and nowadays' memory consumption via malloc and mmap rather than
statically-allocated data.

This adds a BRK_START macro in <vm_param.h> that just tells where we
want to start the brk, and thus removes the _end symbol.

* sysdeps/mach/hurd/i386/vm_param.h: New file.
* sysdeps/mach/hurd/brk.c: Use BRK_START as brk start instead of _end.
Also ignore __data_start.
* hurd/Versions: Remove _end symbol.
* sysdeps/mach/hurd/i386/libc.abilist: Remove _end symbol.

1 files changed, 0 insertions, 3 deletions

diff --git a/hurd/Versions b/hurd/Versions
index f5e8b8c..9b5448a 100644
--- a/hurd/Versions
+++ b/hurd/Versions
@@ -1,8 +1,5 @@
 libc {
   GLIBC_2.0 {
-    # necessary for the Hurd brk implementation
-    _end;
-
     # variables used in macros & inline functions
     __hurd_threadvar_stack_mask; __hurd_threadvar_stack_offset;