From: Tom Stellard <tstellar@redhat.com>
Date: Thu, 16 May 2019 22:36:46 +0000 (+0000)
Subject: Merging r352806:
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=717386938fc075034749cdb91145dc99bb341db1;p=llvm

Merging r352806:

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r352806 | sbc | 2019-01-31 14:38:22 -0800 (Thu, 31 Jan 2019) | 5 lines

[WebAssembly] MC: Fix for outputing wasm object to /dev/null

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D57479
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_80@360949 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/MC/WasmObjectWriter.cpp b/lib/MC/WasmObjectWriter.cpp
index 333748db919..b07fe05cad5 100644
--- a/lib/MC/WasmObjectWriter.cpp
+++ b/lib/MC/WasmObjectWriter.cpp
@@ -368,7 +368,13 @@ void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
 // Now that the section is complete and we know how big it is, patch up the
 // section size field at the start of the section.
 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
-  uint64_t Size = W.OS.tell() - Section.PayloadOffset;
+  uint64_t Size = W.OS.tell();
+  // /dev/null doesn't support seek/tell and can report offset of 0.
+  // Simply skip this patching in that case.
+  if (!Size)
+    return;
+
+  Size -= Section.PayloadOffset;
   if (uint32_t(Size) != Size)
     report_fatal_error("section size does not fit in a uint32_t");
 
diff --git a/test/MC/WebAssembly/null-output.s b/test/MC/WebAssembly/null-output.s
new file mode 100644
index 00000000000..a25d095e0cb
--- /dev/null
+++ b/test/MC/WebAssembly/null-output.s
@@ -0,0 +1,10 @@
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -o /dev/null < %s
+
+    .text
+    .section .text.main,"",@
+    .type    main,@function
+main:
+    .functype   main (i32, i32) -> (i32)
+    end_function
+.Lfunc_end0:
+    .size main, .Lfunc_end0-main