From: John Ousterhout <ouster@cs.stanford.edu>
Date: Thu, 17 Dec 2015 19:29:13 +0000 (-0800)
Subject: Fixes exec-bound-3 failures
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=commitdiff_plain;h=bd5dde3034714da175496292c92dc5a37509a311

Fixes exec-bound-3 failures

The boundary position wasn't being properly chosen (must ensure that
the dst array in boundary.c is always in the last page of the .bss
segment).
---

diff --git a/src/lib/user/user.lds b/src/lib/user/user.lds
index cc6d6c0..1bf30b1 100644
--- a/src/lib/user/user.lds
+++ b/src/lib/user/user.lds
@@ -16,7 +16,7 @@ SECTIONS
   . = DATA_SEGMENT_ALIGN (0x1000, 0x1000);
 
   .data : { *(.data) }
-  .bss : { *(.bss) }
+  .bss : { *(.bss) *(.testEndmem) }
 
   /* Stabs debugging sections.  */
   .stab          0 : { *(.stab) }
diff --git a/src/tests/userprog/boundary.c b/src/tests/userprog/boundary.c
index 2e81df4..ca4fb73 100644
--- a/src/tests/userprog/boundary.c
+++ b/src/tests/userprog/boundary.c
@@ -7,7 +7,10 @@
 #include <string.h>
 #include "tests/userprog/boundary.h"
 
-static char dst[8192];
+/* Together with statements in src/lib/user/user.lds, arranges
+   for the following array to be at the very end of the .bss
+   segment (needed for get_bad_boundary below). */
+static char dst[8192] __attribute__ ((section (".testEndmem,\"aw\",@nobits#")));
 
 /* Returns the beginning of a page.  There are at least 2048
    modifiable bytes on either side of the pointer returned. */
@@ -32,9 +35,9 @@ copy_string_across_boundary (const char *src)
 }
 
 /* Returns an address that is invalid, but the preceding bytes
- * are all valid. Used to position information such that the
- * first byte of the information is valid, but not all the
- * information is valid. */
+ * are all valid (the highest address in the bss segment). Used
+ * to position information such that the first byte of the
+ * information is valid, but not all the information is valid. */
 void *
 get_bad_boundary (void)
 {
diff --git a/src/tests/userprog/exec-bound-3.c b/src/tests/userprog/exec-bound-3.c
index 67937c8..41f1cd9 100644
--- a/src/tests/userprog/exec-bound-3.c
+++ b/src/tests/userprog/exec-bound-3.c
@@ -14,5 +14,15 @@ test_main (void)
   char *p = get_bad_boundary () - 1;
   *p = 'a';
   exec(p);
+
+  /* Note: if this test fails to pass even with the official solutions,
+     it's probably because memory layout has changed and p no longer
+     refers to the proper page boundary. To fix the problem, uncomment
+     the line below to print out the boundary address. In addition,
+     add a printf line in load_segment to print out the address range
+     of each segment. From that, you'll be able to figure out how to
+     modify get_bad_boundary to make things work again. */
+
+  // msg("boundary address: 0x%x", p);
   fail ("should have killed process");
 }