[lld] 0fd5e7b - [WebAssembly][lld] Fix segfault on .bss sections in mapfile

[Thomas Lively via llvm-commits]

Author: Thomas Lively
Date: 2021-07-07T23:31:48-07:00
New Revision: 0fd5e7b2d8ca4ed46d76187feb4b903ed0a3ea75

URL: https://github.com/llvm/llvm-project/commit/0fd5e7b2d8ca4ed46d76187feb4b903ed0a3ea75
DIFF: https://github.com/llvm/llvm-project/commit/0fd5e7b2d8ca4ed46d76187feb4b903ed0a3ea75.diff

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

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.

Differential Revision: https://reviews.llvm.org/D102951

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/lld/test/wasm/map-file.s b/lld/test/wasm/map-file.s
index a215cc14d4cc0..9ca2f196f331e 100644
--- a/lld/test/wasm/map-file.s
+++ b/lld/test/wasm/map-file.s
@@ -10,6 +10,9 @@ wasm_global:
 bar:
     .functype bar () -> ()
     i32.const   somedata
+    i32.const   somezeroes
+    drop
+    drop
     end_function
 
 write_global:
@@ -30,9 +33,15 @@ somedata:
     .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 @@ somedata:
 # 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

diff  --git a/lld/wasm/MapFile.cpp b/lld/wasm/MapFile.cpp
index c964efe1e742f..9dbab5046e23a 100644
--- a/lld/wasm/MapFile.cpp
+++ b/lld/wasm/MapFile.cpp
@@ -80,7 +80,9 @@ getSymbolStrings(ArrayRef<Symbol *> syms) {
     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 @@ void lld::wasm::writeMapFile(ArrayRef<OutputSection *> outputSections) {
                     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';