[project @ 2001-10-26 11:59:36 by sewardj]

merge from stable, revs:

  1.41.4.1  +4 -1      fptools/ghc/compiler/nativeGen/AbsCStixGen.lhs
  1.61.4.3  +10 -0     fptools/ghc/driver/mangler/ghc-asm.lprl

  Place a zero word after each reversed vector table, so that the vtbl
  label is really in the section we would like to claim it is in.  This
  is needed for the GC to work correctly.  Fixes a GHCi segfault
  reported by Ryszard Kubiak.

  1.41.4.2  +7 -0      fptools/ghc/compiler/nativeGen/AbsCStixGen.lhs
  1.61.4.4  +18 -0     fptools/ghc/driver/mangler/ghc-asm.lprl

  Add comments, much longer than the fix itself, giving explaination
  for yesterday's dummy-word-after-vtbl fix.

diff --git a/ghc/compiler/nativeGen/AbsCStixGen.lhs b/ghc/compiler/nativeGen/AbsCStixGen.lhs
index f62c174..262b8fc 100644 (file)
--- a/ghc/compiler/nativeGen/AbsCStixGen.lhs
+++ b/ghc/compiler/nativeGen/AbsCStixGen.lhs
@@ -96,7 +96,17 @@ Here we handle top-level things, like @CCodeBlock@s and
 
  gentopcode stmt@(CRetVector lbl _ _ _)
   = genCodeVecTbl stmt                         `thenUs` \ code ->
-    returnUs (StSegment TextSegment : code [StLabel lbl])
+    returnUs (StSegment TextSegment 
+              : code [StLabel lbl, vtbl_post_label_word])
+    where
+       -- We put a dummy word after the vtbl label so as to ensure the label
+       -- is in the same (Text) section as the vtbl it labels.  This is critical
+       -- for ensuring the GC works correctly, although GC crashes due to
+       -- misclassification are much more likely to show up in the interactive 
+       -- system than in compile code.  For details see comment near line 1164 
+       -- of ghc/driver/mangler/ghc-asm.lprl, which contains an analogous fix for 
+       -- the mangled via-C route.
+       vtbl_post_label_word = StData PtrRep [StInt 0]
 
  gentopcode stmt@(CRetDirect uniq absC srt liveness)
   = gencode absC                                      `thenUs` \ code ->

diff --git a/ghc/driver/mangler/ghc-asm.lprl b/ghc/driver/mangler/ghc-asm.lprl
index 8d3f60b..0b1ae8c 100644 (file)
--- a/ghc/driver/mangler/ghc-asm.lprl
+++ b/ghc/driver/mangler/ghc-asm.lprl
@@ -113,6 +113,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.align 3\n";
     $T_HDR_vector   = "\.text\n\t\.align 3\n";
     $T_HDR_direct   = "\.text\n\t\.align 3\n";
+    $T_create_word  = "\t.quad";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^hppa/ ) {
@@ -140,6 +141,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\t.SPACE \$TEXT\$\n\t.SUBSPA \$CODE\$\n\t\.align 4\n";
     $T_HDR_vector   = "\t.SPACE \$TEXT\$\n\t.SUBSPA \$CODE\$\n\t\.align 4\n";
     $T_HDR_direct   = "\t.SPACE \$TEXT\$\n\t.SUBSPA \$CODE\$\n\t\.align 4\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^i386-.*-(linuxaout|freebsd2|openbsd|nextstep3|cygwin32|mingw32)$/ ) {
@@ -171,6 +173,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.align 2,0x90\n";
     $T_HDR_vector   = "\.text\n\t\.align 2\n"; # NB: requires padding
     $T_HDR_direct   = "\.text\n\t\.align 2,0x90\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^i386-.*-(solaris2|linux|freebsd|netbsd)$/ ) {
@@ -207,6 +210,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.align 4\n";
     $T_HDR_vector   = "\.text\n\t\.align 4\n"; # NB: requires padding
     $T_HDR_direct   = "\.text\n\t\.align 4\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^m68k-.*-sunos4/ ) {
@@ -234,6 +238,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.even\n";
     $T_HDR_vector   = "\.text\n\t\.even\n";
     $T_HDR_direct   = "\.text\n\t\.even\n";
+    $T_create_word  = "\t.long";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^mips-.*/ ) {
@@ -261,6 +266,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\t\.text\n\t\.align 2\n";
     $T_HDR_vector   = "\t\.text\n\t\.align 2\n";
     $T_HDR_direct   = "\t\.text\n\t\.align 2\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^powerpc-.*|^rs6000-.*/ ) {
@@ -289,6 +295,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "# fast\n\.csect \.text[PR]\n\t\.align 2\n";
     $T_HDR_vector   = "# vector\n\.csect \.data[RW]\n\t\.align 2\n"; #not RO!?
     $T_HDR_direct   = "# direct\n";
+    $T_create_word  = "\t.long";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^sparc-.*-solaris2/ ) {
@@ -316,6 +323,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.align 4\n";
     $T_HDR_vector   = "\.text\n\t\.align 4\n";
     $T_HDR_direct   = "\.text\n\t\.align 4\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } elsif ( $TargetPlatform =~ /^sparc-.*-sunos4/ ) {
@@ -343,6 +351,7 @@ sub init_TARGET_STUFF {
     $T_HDR_fast            = "\.text\n\t\.align 4\n";
     $T_HDR_vector   = "\.text\n\t\.align 4\n";
     $T_HDR_direct   = "\.text\n\t\.align 4\n";
+    $T_create_word  = "\t.word";
 
     #--------------------------------------------------------#
     } else {
@@ -1152,6 +1161,25 @@ sub mangle_asm {
                  print OUTASM $chk[$vectorchk{$symb}];
                } else {
                  print OUTASM &rev_tbl($symb, $chk[$vectorchk{$symb}], 0);
+                  # DO NOT DELETE THE NEXT LINE.  It fixes a rather subtle GC bug 
+                  # which showed up as a segfault reported by Ryszard Kubiak.
+                  # Problem is with vector tables.  They wind up as follows:
+                  #      .word some-word
+                  #      .word some-other-word
+                  #   fooble_vtbl:
+                  # Problem is that we want the label fooble_vtbl to be considered 
+                  # in the same section as the vtbl itself, but the label actually 
+                  # lives at the next word along.  If a data segment should happen 
+                  # to immediately follow the vtbl, as it can in GHCi, the label will 
+                  # be malclassified as in the data rather than text segment (during 
+                  # GC), and so we will regard references to it as static closure 
+                  # pointers rather than as code pointers, which is an error which 
+                  # usually crashes the garbage collectors.
+                  # To fix this, we place a dummy word after the label, so as to
+                  # ensure that the label is in the same segment as the vtbl proper.
+                  # The native code generator has an analogous fix; see
+                  # ghc/compiler/nativeGen/AbsCStixGen.lhs line 107.
+                  print OUTASM "${T_create_word} 0\n";
                }
                # direct return code will be put here!
                $chkcat[$vectorchk{$symb}] = 'DONE ALREADY';