[MachOYAML] Improve section offset misalignment error message

[Michael137]

Summary

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]

llvm/lib/ObjectYAML/MachOEmitter.cpp

 //===----------------------------------------------------------------------===//
 
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/ObjectYAML/DWARFEmitter.h"
 #include "llvm/ObjectYAML/ObjectYAML.h"
 #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"
 
 #include "llvm/Support/Format.h"
 
 using namespace llvm;
 
case MachO::LC_SEGMENT_64:
       }
       for (auto &Sec : LC.Sections) {
         ZeroToOffset(OS, Sec.offset);
         // Zero Fill any data between the end of the last thing we wrote and the
         // start of this section.
         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)));
         // If the section's content is specified in the 'DWARF' entry, we will
         // emit it regardless of the section's segname.
         if (Obj.DWARF.getNonEmptySectionNames().count(SectName.substr(2))) {
           if (Sec.content)
             return createStringError(errc::invalid_argument,

llvm/test/ObjectYAML/MachO/sections.yaml

 #CHECK:       - sectname:        __la_symbol_ptr
 #CHECK:         segname:         __DATA
 
 ## b) Test that yaml2obj emits an error message if we specify an offset that
 ## makes the current section and the previous one overlap.
 
 # 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:
   magic:      0xFEEDFACF
   cputype:    0x01000007
   cpusubtype: 0x80000003
   filetype:   0x00000002
   ncmds:      1