[MachOYAML] Improve section offset misalignment error message

Before:
```
wrote too much data somewhere, section offsets don't line up
```

After:
```
wrote too much data somewhere, section offsets in section __debug_str for segment __DWARF don't line up: [cursor=0x581], [fileStart=0x0], [sectionOffset=0x579]
```

Differential Revision: https://reviews.llvm.org/D140116

2 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/ObjectYAML/MachOEmitter.cpp b/llvm/lib/ObjectYAML/MachOEmitter.cpp
index 022c08e..54983f0 100644
--- a/llvm/lib/ObjectYAML/MachOEmitter.cpp
+++ b/llvm/lib/ObjectYAML/MachOEmitter.cpp
@@ -17,6 +17,7 @@
 #include "llvm/ObjectYAML/yaml2obj.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"
@@ -315,7 +316,12 @@ Error MachOWriter::writeSectionData(raw_ostream &OS) {
         if (OS.tell() - fileStart > Sec.offset && Sec.offset != (uint32_t)0)
           return createStringError(
               errc::invalid_argument,
-              "wrote too much data somewhere, section offsets don't line up");
+              llvm::formatv(
+                  "wrote too much data somewhere, section offsets in "
+                  "section {0} for segment {1} don't line up: "
+                  "[cursor={2:x}], [fileStart={3:x}], [sectionOffset={4:x}]",
+                  Sec.sectname, Sec.segname, OS.tell(), fileStart,
+                  Sec.offset.value));
 
         StringRef SectName(Sec.sectname,
                            strnlen(Sec.sectname, sizeof(Sec.sectname)));
diff --git a/llvm/test/ObjectYAML/MachO/sections.yaml b/llvm/test/ObjectYAML/MachO/sections.yaml
index 76d6205..052c66f 100644
--- a/llvm/test/ObjectYAML/MachO/sections.yaml
+++ b/llvm/test/ObjectYAML/MachO/sections.yaml
@@ -291,7 +291,7 @@ LoadCommands:
 
 # RUN: not yaml2obj --docnum=2 %s -o %t2.macho 2>&1 | FileCheck %s --check-prefix=OVERLAP
 
-# OVERLAP: yaml2obj: error: wrote too much data somewhere, section offsets don't line up
+# OVERLAP: yaml2obj: error: wrote too much data somewhere, section offsets in section __sec2 for segment __SEC don't line up: [cursor=0x121], [fileStart=0x0], [sectionOffset=0x1]
 
 --- !mach-o
 FileHeader: