[diffoscope] 01/03: Add fallbacks to elf code section disassembly. (Closes: #879003)

[Ximin Luo]

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commit bfbb1223e16d80f688d5236c7451313a661f629d
Author: Mike Hommey <mh at glandium.org>
Date:   Fri Oct 20 21:48:24 2017 +0900

    Add fallbacks to elf code section disassembly. (Closes: #879003)
    
    Because objdump --line-numbers can be extremely slow, it can be worth
    skipping it, and just get a disassembly (especially when the files don't
    contain line numbers debug info, where ironically, objdump is slow with
    --line-numbers).
    
    The --exclude-command command line option allows to skip some commands,
    and one can use that to skip the command that uses --line-numbers, but
    in that case, no difference is shown for the code sections.
    
    This change adds a fallback in that case, where objdump is called
    without the --line-numbers command, making disassembly faster.
    
    But that can still be too time consuming (especially because the output
    can be large, and diffing that can be a long process, so allow to
    exclude /that/ too, and fallback to an hexdump in that case.
---
 diffoscope/comparators/elf.py | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/diffoscope/comparators/elf.py b/diffoscope/comparators/elf.py
index 0a7d29b..c572601 100644
--- a/diffoscope/comparators/elf.py
+++ b/diffoscope/comparators/elf.py
@@ -241,6 +241,11 @@ class ObjdumpDisassembleSection(ObjdumpSection):
         return ObjdumpDisassembleSection.RE_SYMBOL_COMMENT.sub(r'\1', line)
 
 
+class ObjdumpDisassembleSectionNoLineNumbers(ObjdumpDisassembleSection):
+    def objdump_options(self):
+        return ['--disassemble', '--demangle']
+
+
 READELF_COMMANDS = (
     ReadelfFileHeader,
     ReadelfProgramHeader,
@@ -328,12 +333,20 @@ class ElfSection(File):
 
 class ElfCodeSection(ElfSection):
     def compare(self, other, source=None):
+        # Normally disassemble with line numbers, but if the command is
+        # excluded, fallback to disassembly, and if that is also excluded,
+        # fallback to a hexdump.
         return Difference.from_command(
             ObjdumpDisassembleSection,
             self.path,
             other.path,
             command_args=[self._name],
-        )
+        ) or Difference.from_command(
+            ObjdumpDisassembleSectionNoLineNumbers,
+            self.path,
+            other.path,
+            command_args=[self._name],
+        ) or super().compare(other, source)
 
 
 class ElfStringSection(ElfSection):

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