Correctly parse ELF for musllinux on Big Endian

[uranusjr]

Based on test binary provided in #473 (comment)

Note that this does not actually fix anything. The current implementation would yield the correct result on a BE system when reading a BE Python interpreter, which is what should happen (a Python interpreter with non-matching endian won’t run to begin with). This simply makes the logic more explicit so the unit tests pass on a BE system, even though they only test parsing LE executables.

[glaubitz]

This still fails for me with the following error:

[   98s] =================================== FAILURES ===================================
[   98s] ______________ test_parse_ld_musl_from_elf_no_interpreter_section ______________
[   98s] 
[   98s]     def test_parse_ld_musl_from_elf_no_interpreter_section():
[   98s]         with BIN_MUSL_X86_64.open("rb") as f:
[   98s]             data = f.read()
[   98s]     
[   98s]         # Change all sections to *not* PT_INTERP.
[   98s]         unpacked = struct.unpack("16BHHIQQQIHHH", data[:58])
[   98s]         *_, e_phoff, _, _, _, e_phentsize, e_phnum = unpacked
[   98s]         for i in range(e_phnum + 1):
[   98s]             sb = e_phoff + e_phentsize * i
[   98s]             se = sb + 56
[   98s] >           section = struct.unpack("IIQQQQQQ", data[sb:se])
[   98s] E           struct.error: unpack requires a buffer of 56 bytes
[   98s] 
[   98s] tests/test_musllinux.py:110: error
[   98s] ============================== 2 tests deselected ==============================
[   98s] ======= 1 failed, 29293 passed, 2 deselected, 1 xfailed in 47.12 seconds =======

Tested on SUSE Linux Enterprise Server 15 with Python 3.6.

[uranusjr]

Ah, right, it’s because the test still uses endian-sensitive rules.

[uranusjr]

I pushed a change for that specific test; does this work?

In the long term I think we should probably extract the ELF parsing logic into a common class that can be used across musllinux, manylinux, and in test code.

[glaubitz]

I pushed a change for that specific test; does this work?

Unfortunately not:

[   87s] =================================== FAILURES ===================================
[   87s] ______________ test_parse_ld_musl_from_elf_no_interpreter_section ______________
[   87s] 
[   87s]     def test_parse_ld_musl_from_elf_no_interpreter_section():
[   87s]         with BIN_MUSL_X86_64.open("rb") as f:
[   87s]             data = f.read()
[   87s]     
[   87s]         # Change all sections to *not* PT_INTERP. We are explicitly using LSB rules
[   87s]         # because the binaries are in LSB.
[   87s] >       unpacked = struct.unpack("16B<HHIQQQIHHH", data[:58])
[   87s] E       struct.error: bad char in struct format
[   87s] 
[   87s] tests/test_musllinux.py:106: error
[   87s] ============================== 2 tests deselected ==============================

[uranusjr]

LOL because I messed it up. It should be <16BHHIQQQIHHH, not 16B<HHIQQQIHHH. Try that instead.

[glaubitz]

Works now, thanks!