[all-commits] [llvm/llvm-project] 55b141: [lldb] Fix a bug for PT_TLS segments getting loade...

[Greg Clayton via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 55b1410895b69d8e4517f6a2a2978b414b4ecac3
      https://github.com/llvm/llvm-project/commit/55b1410895b69d8e4517f6a2a2978b414b4ecac3
  Author: Greg Clayton <gclayton at fb.com>
  Date:   2024-07-11 (Thu, 11 Jul 2024)

  Changed paths:
    M lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
    M lldb/test/Shell/ObjectFile/ELF/PT_TLS-overlap-PT_LOAD.yaml

  Log Message:
  -----------
  [lldb] Fix a bug for PT_TLS segments getting loaded when they shouldn't. (#98432)

PT_LOAD and PT_TLS segments are top level sections in the ObjectFileELF
section list. The two segments can often have the same program header
p_vaddr and p_paddr values and this can cause section load list issues
in LLDB if we load the PT_TLS segments. What happens is the
SectionLoadList::m_addr_to_sect, when a library is loaded, will first
map one of the sections named "PT_LOAD[0]" with the load address that
matches the p_vaddr entry from the program header. Then the "PT_TLS[0]"
would come along and try to load this section at the same address. This
would cause the "PT_LOAD[0]" section to be unloaded as the
SectionLoadList::m_addr_to_sect would replace the value for the matching
p_vaddr with the last section to be seen. The sizes of the PT_TLS and
PT_LOAD that have the same p_vaddr value don't need to have the same
byte size, so this could cause lookups to fail for an addresses in the
"PT_LOAD[0]" section or any of its children if the offset is greater
than the offset size of the PT_TLS segment. It could also cause us to
incorrectly attribute addresses from the "PT_LOAD[0]" to the "PT_TLS[0]"
segment when doing lookups for offset that are less than the size of the
PT_TLS segment.

This fix stops us from loading PT_TLS segments in the section load lists
and will prevent the bugs that resulted from this. No addresses the the
DWARF refer to TLS data with a "file address" in any way. They all have
TLS DWARF location expressions to locate these variables. We also don't
have any support for having actual thread specific sections and having
those sections resolve to something different for each thread, so there
currently is no point in loading thread specific sections. Both the
ObjectFileMachO and ObjectFileCOFF both ignore thread specific sections
at the moment, so this brings the ObjectFileELF to parity with those
plug-ins.

I added a test into an existing test to verify that things work as
expected.

Prior to this fix with a real binary, the output of "target dump
section-load-list" would look like this for the old LLDB:
```
// (lldb) target dump section-load-list
// addr = 0x0000000000000000, section = 0x55d46ab8c510: 0xfffffffffffffffd container        [0x0000000000000000-0x0000000000000628)  r--  0x00000000 0x00000628 0x00000000 a.out.PT_LOAD[0]
// addr = 0x0000000000001000, section = 0x55d46ab8b0c0: 0xfffffffffffffffc container        [0x0000000000001000-0x0000000000001185)  r-x  0x00001000 0x00000185 0x00000000 a.out.PT_LOAD[1]
// addr = 0x0000000000002000, section = 0x55d46ac040f0: 0xfffffffffffffffb container        [0x0000000000002000-0x00000000000020cc)  r--  0x00002000 0x000000cc 0x00000000 a.out.PT_LOAD[2]
// addr = 0x0000000000003db0, section = 0x55d46ab7cef0: 0xfffffffffffffff6 container        [0x0000000000003db0-0x0000000000003db4)  r--  0x00002db0 0x00000000 0x00000000 a.out.PT_TLS[0]
```
And this for the fixed LLDB:
```
// (lldb) target dump section-load-list
// addr = 0x0000000000000000, section = 0x105f0a9a8: 0xfffffffffffffffd container        [0x0000000000000000-0x0000000000000628)  r--  0x00000000 0x00000628 0x00000000 a.out.PT_LOAD[0]
// addr = 0x0000000000001000, section = 0x105f0adb8: 0xfffffffffffffffc container        [0x0000000000001000-0x0000000000001185)  r-x  0x00001000 0x00000185 0x00000000 a.out.PT_LOAD[1]
// addr = 0x0000000000002000, section = 0x105f0af48: 0xfffffffffffffffb container        [0x0000000000002000-0x00000000000020cc)  r--  0x00002000 0x000000cc 0x00000000 a.out.PT_LOAD[2]
// addr = 0x0000000000003db0, section = 0x105f0b078: 0xfffffffffffffffa container        [0x0000000000003db0-0x0000000000004028)  rw-  0x00002db0 0x00000274 0x00000000 a.out.PT_LOAD[3]
```
We can see that previously the "PT_LOAD[3]" segment would be removed
from the section load list, and after the fix it remains and there is on
PT_TLS in the loaded sections.



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