commit 03da1e53c24aa86a3b04216c3d2d002fd9020ea0
author Timothy M. Jones <tjones1@inf.ed.ac.uk> Sat Oct 24 10:53:58 2009 -0700
committer Timothy M. Jones <tjones1@inf.ed.ac.uk> Sat Oct 24 10:53:58 2009 -0700
tree 8b562fe53646a789df61bf514669a1b60bd08777
parent cc21f862e2d6ad6ba8d5332d6bbc05e58e55bfa0

syscall: Zero out memory that already exists during the brk system call.

Glibc often assumes that memory it receives from the kernel after a brk
system call will contain only zeros. This is important during a calloc,
because it won't clear the new memory itself. In the simulator, if the
new page exists, it will be cleared using this patch, to mimic the kernel's
functionality.

src/sim/syscall_emul.cc

diff --git a/src/sim/syscall_emul.cc b/src/sim/syscall_emul.cc
index 9a797bc..13ad043 100644
--- a/src/sim/syscall_emul.cc
+++ b/src/sim/syscall_emul.cc
@@ -144,6 +144,24 @@
             if (!p->pTable->translate(gen.addr()))
                 p->pTable->allocate(roundDown(gen.addr(), VMPageSize),
                                     VMPageSize);
+
+            // if the address is already there, zero it out
+            else {
+                uint8_t zero  = 0;
+                TranslatingPort *tp = tc->getMemPort();
+
+                // split non-page aligned accesses
+                Addr next_page = roundUp(gen.addr(), VMPageSize);
+                uint32_t size_needed = next_page - gen.addr();
+                tp->memsetBlob(gen.addr(), zero, size_needed);
+                if (gen.addr() + VMPageSize > next_page &&
+                    next_page < new_brk &&
+                    p->pTable->translate(next_page))
+                {
+                    size_needed = VMPageSize - size_needed;
+                    tp->memsetBlob(next_page, zero, size_needed);
+                }
+            }
         }
     }