[PATCH] D102951: [WebAssembly][lld] Fix segfault on .bss sections in mapfile

[Thomas Lively via Phabricator via llvm-commits]

tlively created this revision.
tlively added a reviewer: sbc100.
Herald added subscribers: wingo, ecnelises, sunfish, jgravelle-google, dschuff.
tlively requested review of this revision.
Herald added subscribers: llvm-commits, aheejin.
Herald added a project: LLVM.

When memory is declared in the Wasm module, we rely on the implicit zero
initialization behavior and do not explicitly output .bss sections. The means
that they do not have associated `outputSec` entries, which was causing
segfaults in the mapfile support. Fix the issue by guarding against null
`outputSec` and falling back to using a zero offset.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102951

Files:
  lld/test/wasm/map-file.s
  lld/wasm/MapFile.cpp


Index: lld/wasm/MapFile.cpp
===================================================================
--- lld/wasm/MapFile.cpp
+++ lld/wasm/MapFile.cpp
@@ -80,7 +80,9 @@
     auto *chunk = syms[i]->getChunk();
     if (chunk == nullptr)
       return;
-    uint64_t fileOffset = chunk->outputSec->getOffset() + chunk->outSecOff;
+    uint64_t fileOffset = chunk->outputSec != nullptr
+                              ? chunk->outputSec->getOffset() + chunk->outSecOff
+                              : 0;
     uint64_t vma = -1;
     uint64_t size = 0;
     if (auto *DD = dyn_cast<DefinedData>(syms[i])) {
@@ -138,9 +140,11 @@
                     oseg->size);
         os << oseg->name << '\n';
         for (auto *chunk : oseg->inputSegments) {
-          writeHeader(os, chunk->getVA(),
-                      chunk->outputSec->getOffset() + chunk->outSecOff,
-                      chunk->getSize());
+          uint64_t offset =
+              chunk->outputSec != nullptr
+                  ? chunk->outputSec->getOffset() + chunk->outSecOff
+                  : 0;
+          writeHeader(os, chunk->getVA(), offset, chunk->getSize());
           os.indent(8) << toString(chunk) << '\n';
           for (Symbol *sym : sectionSyms[chunk])
             os << symStr[sym] << '\n';
Index: lld/test/wasm/map-file.s
===================================================================
--- lld/test/wasm/map-file.s
+++ lld/test/wasm/map-file.s
@@ -10,6 +10,9 @@
 bar:
     .functype bar () -> ()
     i32.const   somedata
+    i32.const   somezeroes
+    drop
+    drop
     end_function
 
 write_global:
@@ -30,9 +33,15 @@
     .int32 123
 .size somedata, 4
 
+.section .bss.somezeroes,"",@
+somezeroes:
+    .int32 0
+.size somezeroes, 4
+
 .section .debug_info,"",@
     .int32 bar
 
+
 #      CHECK:    Addr      Off     Size Out     In      Symbol
 # CHECK-NEXT:       -        8        a TYPE
 # CHECK-NEXT:       -       12        6 FUNCTION
@@ -42,19 +51,22 @@
 # CHECK-NEXT:       0        0        0         __stack_pointer
 # CHECK-NEXT:       1        0        0         wasm_global
 # CHECK-NEXT:       -       33       15 EXPORT
-# CHECK-NEXT:       -       48       26 CODE
-# CHECK-NEXT:       -       49        9         {{.*}}{{/|\\}}map-file.s.tmp1.o:(bar)
-# CHECK-NEXT:       -       49        9                 bar
-# CHECK-NEXT:       -       52        b         {{.*}}{{/|\\}}map-file.s.tmp1.o:(write_global)
-# CHECK-NEXT:       -       52        b                 write_global
-# CHECK-NEXT:       -       5d        f         {{.*}}{{/|\\}}map-file.s.tmp1.o:(_start)
-# CHECK-NEXT:       -       5d        f                 _start
-# CHECK-NEXT:       -       6e        d DATA
-# CHECK-NEXT:     400       6f        4 .data
-# CHECK-NEXT:     400       75        4         {{.*}}{{/|\\}}map-file.s.tmp1.o:(.data.somedata)
-# CHECK-NEXT:     400       75        4                 somedata
-# CHECK-NEXT:       -       7b       12 CUSTOM(.debug_info)
-# CHECK-NEXT:       -       8d       50 CUSTOM(name)
+# CHECK-NEXT:       -       48       2e CODE
+# CHECK-NEXT:       -       49       11         {{.*}}{{/|\\}}map-file.s.tmp1.o:(bar)
+# CHECK-NEXT:       -       49       11                 bar
+# CHECK-NEXT:       -       5a        b         {{.*}}{{/|\\}}map-file.s.tmp1.o:(write_global)
+# CHECK-NEXT:       -       5a        b                 write_global
+# CHECK-NEXT:       -       65        f         {{.*}}{{/|\\}}map-file.s.tmp1.o:(_start)
+# CHECK-NEXT:       -       65        f                 _start
+# CHECK-NEXT:       -       76        d DATA
+# CHECK-NEXT:     400       77        4 .data
+# CHECK-NEXT:     400       7d        4         {{.*}}{{/|\\}}map-file.s.tmp1.o:(.data.somedata)
+# CHECK-NEXT:     400       7d        4                 somedata
+# CHECK-NEXT:     404       76        4 .bss
+# CHECK-NEXT:     404        0        4         {{.*}}{{/|\\}}map-file.s.tmp1.o:(.bss.somezeroes)
+# CHECK-NEXT:     404        0        4                 somezeroes
+# CHECK-NEXT:       -       83       12 CUSTOM(.debug_info)
+# CHECK-NEXT:       -       95       50 CUSTOM(name)
 
 # RUN: not wasm-ld %t1.o -o /dev/null -Map=/ 2>&1 \
 # RUN:  | FileCheck -check-prefix=FAIL %s


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