[Lldb-commits] [lldb] Add support for reading the dynamic symbol table from PT_DYNAMIC (PR #112596)

[Pavel Labath via lldb-commits]

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+## This test verifies that loading an ELF file that has no section headers can
+## load the dynamic symbol table using the DT_SYMTAB, DT_SYMENT, DT_HASH or
+## the DT_GNU_HASH .dynamic key/value pairs that are loaded via the PT_DYNAMIC
+## segment.
+##
+## This test will convert a shared library from yaml, strip its section headers,
+## and varify that LLDB can load the dynamic symbol table. We must manually
+## strip the section headers from a full shared library because our ELF YAML
+## support in obj2yaml/yaml2obj doesn't support ELF files with program headers
+## only, they must have sections or the file doesn't get recreated correctlty.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-strip --strip-sections %t -o %t.noshdrs
+
+# RUN: %lldb -b \
+# RUN:   -o "target create -d '%t.noshdrs'" \
+# RUN:   -o "image dump objfile" \
+# RUN:   | FileCheck %s --dump-input=always
+# CHECK: (lldb) image dump objfile
+# CHECK: Dumping headers for 1 module(s).
+# CHECK: ObjectFileELF, file =
+# CHECK: ELF Header
+# Make sure there are no section headers
+# CHECK: e_shnum = 0x00000000
+# Make sure we were able to load the symbols
+# CHECK: elf-dynsym.yaml.tmp.noshdrs, num_symbols = 9:
+# CHECK: [ 0] 1 Undefined 0x0000000000000000 0x0000000000000000 0x00000022 __cxa_finalize
+# CHECK: [ 1] 2 X Undefined 0x0000000000000000 0x0000000000000000 0x00000012 puts
+# CHECK: [ 2] 3 Undefined 0x0000000000000000 0x0000000000000000 0x00000020 _ITM_deregisterTMCloneTable
+# CHECK: [ 3] 4 Undefined 0x0000000000000000 0x0000000000000000 0x00000020 __gmon_start__
+# CHECK: [ 4] 5 Undefined 0x0000000000000000 0x0000000000000000 0x00000020 _ITM_registerTMCloneTable
+# CHECK: [ 5] 6 X Code 0x0000000000001135 0x0000000000000016 0x00000012 baz()
+# CHECK: [ 6] 7 X Code 0x000000000000111f 0x0000000000000016 0x00000012 bar()
+# CHECK: [ 7] 8 X Code 0x000000000000114b 0x0000000000000016 0x00000012 biz()
+# CHECK: [ 8] 9 X Code 0x0000000000001109 0x0000000000000016 0x00000012 foo()
+
+--- !ELF
----------------
labath wrote:

This input contains a lot of data that's irrelevant for the test. Can you make it smaller? For example, something like `llvm-mc -triple=x86_64-pc-linux -filetype=obj -o - - <<<".globl defined, undefined; defined:" | ld.lld /dev/stdin -o - --hash-style=gnu -export-dynamic` produces a much smaller file which still has a dynamic section, and you can control exactly which entries it contains (in practice you may want to expand the input slightly, just so that all the symbols don't end up with the same value).

You could yamlize that, or even just leave that as the input to the test itself (it should be deterministic enough). If you go with the second option, you can add `-z nosectionheader` to the linker command to skip the `llvm-strip` step.

I think think that another test with the DT_HASH hash style would be in order (just change the above command to --hash-style=sysv)

https://github.com/llvm/llvm-project/pull/112596