[Lldb-commits] [PATCH] D132954: lldb: Add support for R_386_32 relocations to ObjectFileELF

Mon Sep 5 07:24:26 PDT 2022

labath added a comment.

In D132954#3767083 <https://reviews.llvm.org/D132954#3767083>, @dmlary wrote:

> @labath it doesn't look like the relocations are applied during `lldb-test object-file --contents`:

I'm definitely seeing `ObjectFileELF::RelocateSection` be invoked with this command (I'm using it on a random .o file from my lldb build). Could you step through the function to see why that does not happen for you?

  * frame #0: 0x0000555556916576 lldb-test`ObjectFileELF::RelocateSection(this=0x0000555564473a60, section=0x00005555645310e0) at ObjectFileELF.cpp:2857:26
    frame #1: 0x00005555564b50de lldb-test`lldb_private::ObjectFile::ReadSectionData(this=0x0000555564473a60, section=0x00005555645310e0, section_data=0x00007fffffffce80) at ObjectFile.cpp:530:20
    frame #2: 0x00005555569187e1 lldb-test`ObjectFileELF::ReadSectionData(this=0x0000555564473a60, section=0x00005555645310e0, section_data=0x00007fffffffce80) at ObjectFileELF.cpp:3350:46
    frame #3: 0x00005555562f0c7c lldb-test`lldb_private::Section::GetSectionData(this=0x00005555645310e0, section_data=0x00007fffffffce80) at Section.cpp:381:39

> from obj2yaml for rel.c described in summary (with added spacing for readabilty):
>
>   [...]
>     - Name:            .debug_info
>       Type:            SHT_PROGBITS
>       AddressAlign:    0x1
>       Content:
>         74000000 04000000 00000401 09000000 01890000 00620000 00000000 00023400
>         00002D00 0000032D 0000001F 00040407 00000000 04010684 00000005 7C000000
>         01024C00 00000503 00000000 061D0000 00023400 00006100 0000032D 00000004
>         00077661 72000103 72000000 05030000 00000651 00000000
>   [...]
>     - Name:            .rel.debug_info
>       Type:            SHT_REL
>       Flags:           [ SHF_INFO_LINK ]
>       Link:            .symtab
>       AddressAlign:    0x4
>       Info:            .debug_info
>       Relocations:
>         - Offset:          0x6
>           Symbol:          .debug_abbrev
>           Type:            R_386_32
>         - Offset:          0xC
>           Symbol:          .debug_str
>           Type:            R_386_32
>         - Offset:          0x11
>   [...]
>
> output for `.debug_info` from `lldb-test object-file --contents rel.o`:
>
>   txt
>     Index: 3
>     ID: 0x4
>     Name: .debug_info
>     Type: dwarf-info
>     Permissions: ---
>     Thread specific: no
>     VM address: 0x0
>     VM size: 0
>     File size: 120
>     Data:  (
>         0000: 74000000 04000000 00000401 09000000 01890000 00620000 00000000 00023400  |t....................b........4.|
>         0020: 00002D00 0000032D 0000001F 00040407 00000000 04010684 00000005 7C000000  |..-....-....................|...|
>         0040: 01024C00 00000503 00000000 061D0000 00023400 00006100 0000032D 00000004  |..L...............4...a....-....|
>         0060: 00077661 72000103 72000000 05030000 00000651 00000000                    |..var...r..........Q....|
>     )
>
> I would expect at least one byte in the output to be changed if relocations were being applied to `.debug_info`.  To ensure it's not just relocating using a base address of 0, I modified one relocation to use `var` as the symbol for relocation; it has a non-zero offset within its section.  Even in that case there were no modifications made to the data in `.debug_info`.
>
> It looks like I'll need to build a binary and a separate object file in the test case.  Any chance you know of a test off-hand building multiple things, with specific flags?

That will be a bit messy. I'd rather figure out what's going on with the lldb-test command..

Repository:
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https://reviews.llvm.org/D132954