From: Florian Krohm <florian@eich-krohm.de>
Date: Thu, 26 Feb 2015 21:48:19 +0000 (+0000)
Subject: Simplify do_brk
X-Git-Tag: svn/VALGRIND_3_11_0~625
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=eb4228077ac39f60a983a532e32b2968284ef93c;p=thirdparty%2Fvalgrind.git

Simplify do_brk
- remove redundant asserts
- let VG_(am_extend_into_adjacent_reservation_client) worry about
  - whether delta is too large
  - whether the segment abutting this one exists and is a reservation
    segment
  The function already checks these things. No need to do it again here.
- do_brk does not need to know that a reservation segment must not
  shrink beyond a single page. That detail ought to be hidden in
  the address space manager.
Also, turn a few conditions into asserts.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14967
---

diff --git a/coregrind/m_syswrap/syswrap-generic.c b/coregrind/m_syswrap/syswrap-generic.c
index d6a460bef8..be32e7a0f3 100644
--- a/coregrind/m_syswrap/syswrap-generic.c
+++ b/coregrind/m_syswrap/syswrap-generic.c
@@ -1,3 +1,4 @@
+/* -*- mode: C; c-basic-offset: 3; -*- */
 
 /*--------------------------------------------------------------------*/
 /*--- Wrappers for generic Unix system calls                       ---*/
@@ -1187,7 +1188,6 @@ void ML_(buf_and_len_post_check) ( ThreadId tid, SysRes res,
 static Addr do_brk ( Addr newbrk )
 {
    NSegment const* aseg;
-   NSegment const* rseg;
    Addr newbrkP;
    SizeT delta;
    Bool debug = False;
@@ -1196,19 +1196,19 @@ static Addr do_brk ( Addr newbrk )
       VG_(printf)("\ndo_brk: brk_base=%#lx brk_limit=%#lx newbrk=%#lx\n",
 		  VG_(brk_base), VG_(brk_limit), newbrk);
 
-#  if 0
-   if (0) show_segments("in_brk");
-#  endif
+   if (0) VG_(am_show_nsegments)(0, "in_brk");
 
    if (newbrk < VG_(brk_base))
       /* Clearly impossible. */
       goto bad;
 
-   if (newbrk >= VG_(brk_base) && newbrk < VG_(brk_limit)) {
+   if (newbrk < VG_(brk_limit)) {
       /* shrinking the data segment.  Be lazy and don't munmap the
          excess area. */
       NSegment const * seg = VG_(am_find_nsegment)(newbrk);
-      if (seg && seg->hasT)
+      vg_assert(seg);
+
+      if (seg->hasT)
          VG_(discard_translations)( newbrk, VG_(brk_limit) - newbrk, 
                                     "do_brk(shrink)" );
       /* Since we're being lazy and not unmapping pages, we have to
@@ -1218,15 +1218,16 @@ static Addr do_brk ( Addr newbrk )
          try hard to ensure we're not going to segfault by doing the
          write - check both ends of the range are in the same segment
          and that segment is writable. */
-      if (seg) {
-         /* pre: newbrk < VG_(brk_limit) 
-              => newbrk <= VG_(brk_limit)-1 */
-         NSegment const * seg2;
-         vg_assert(newbrk < VG_(brk_limit));
+      NSegment const * seg2;
+
+      if (VG_(brk_limit) > VG_(brk_base))
          seg2 = VG_(am_find_nsegment)( VG_(brk_limit)-1 );
-         if (seg2 && seg == seg2 && seg->hasW)
-            VG_(memset)( (void*)newbrk, 0, VG_(brk_limit) - newbrk );
-      }
+      else
+         seg2 = VG_(am_find_nsegment)( VG_(brk_limit) );
+      vg_assert(seg2);
+
+      if (seg == seg2 && seg->hasW)
+         VG_(memset)( (void*)newbrk, 0, VG_(brk_limit) - newbrk );
 
       VG_(brk_limit) = newbrk;
       return newbrk;
@@ -1237,31 +1238,19 @@ static Addr do_brk ( Addr newbrk )
       aseg = VG_(am_find_nsegment)( VG_(brk_limit)-1 );
    else
       aseg = VG_(am_find_nsegment)( VG_(brk_limit) );
-   rseg = VG_(am_next_nsegment)( aseg, True/*forwards*/ );
 
    /* These should be assured by setup_client_dataseg in m_main. */
    vg_assert(aseg);
-   vg_assert(rseg);
    vg_assert(aseg->kind == SkAnonC);
-   vg_assert(rseg->kind == SkResvn);
-   vg_assert(aseg->end+1 == rseg->start);
 
-   vg_assert(newbrk >= VG_(brk_base));
-   if (newbrk <= rseg->start) {
+   if (newbrk <= aseg->end + 1) {
       /* still fits within the anon segment. */
       VG_(brk_limit) = newbrk;
       return newbrk;
    }
 
-   if (newbrk > rseg->end+1 - VKI_PAGE_SIZE) {
-      /* request is too large -- the resvn would fall below 1 page,
-         which isn't allowed. */
-      goto bad;
-   }
-
    newbrkP = VG_PGROUNDUP(newbrk);
-   vg_assert(newbrkP > rseg->start && newbrkP <= rseg->end+1 - VKI_PAGE_SIZE);
-   delta = newbrkP - rseg->start;
+   delta = newbrkP - (aseg->end + 1);
    vg_assert(delta > 0);
    vg_assert(VG_IS_PAGE_ALIGNED(delta));