[Android][cross-compile][glang][gdb][BFD:unable to initialize decompress status for section .debug_loclists]

[xiaoqiang-wang]

Hello,
I'm an Android-Source-Code and ARM-GPU-DRIVER-Source-Code user.
When I try to use default compile tool-chain clang-18.0.1 (prebuilts/clang/host/linux-x86/clang-r522817/),
There is something wrong,
I can NOT use gdb to debug the clang-18.0.1 generated ELF file.

When I update from clang-18.0.1 to clang-19.0.1(prebuilts/clang/host/linux-x86/clang-r536225/bin/clang), the problem still exist.

I sincerely want yours can kindly help me about below Question_1 and Question_2.

===

1.Currently, the GPU-DRIVER-Source-Code can be compiled and used in the Android-Source-Code successfully, and It's output the malisc_host ELF file.

2.But when I try to use "gdb malisc_host" command to debug, It show below error message.

Android_15$ gdb  ./malisc_host
    BFD: malisc_host: unable to initialize decompress status for section .debug_loclists
    malisc_host: not in executable format: file format not recognized

3.But the malisc_host can be debug by latest lldb-21.0.0 tool.

lldb ./malisc_host //OK it works

4.The the output binary file malisc_host can be debug by lldb, but can NOT be debug by gdb.
4.1. But the lldb is not a powerful tool, It can NOT stop on my added breakpoints.
4.2. So, I strongly want to use the gdb to debug the malisc_host ELF.

5. And when I use the readelf command, it output below Warning message.
   Warning message .debug_str unsupported compress type: 2

Android_15$ readelf -p .comment out/soong/.intermediates/product/malisc__host/linux_glibc_x86_64/unstripped/malisc_host
readelf: Warning: section '.debug_str' has unsupported compress type: 2

String dump of section '.comment':
  [     0]  GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3
  [    2a]  GCC: (GNU) 4.8.3
  [    3c]  Android (11967740, +pgo, +bolt, +lto, +mlgo, based on r522817) clang version 18.0.1 (https://android.googlesource.com/toolchain/llvm-project d8003a456d14a3deb8054cdaa529ffbf02d9b262)
  [    f3]  Linker: LLD 18.0.1

Above readelf command output the warning message:
5.1. I think in the clang generated ELF 's file header,
There must be something's version or format UN-Match with gdb's expectation.
that lead to gdb can not correctly recognize the malisc_host's format.

Questions_1

Q1.1 Does this message mean the malisc_host's file header have be corrupted by clang,
or clang give a different value to the malisc_host ELF's debug_section.
Q1.2 How can we fix this error? and make gdb can debug the clang‘s output ELF malisc_host?
Q1.3 Is this error that is an already known problem in clang-18.0.1/clang-19.0.1?

Below is my Machine info

1.The system's is Ubuntu 20.0.4

Android_15$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.6 LTS
Release:        20.04
Codename:       focal

2.The clang/clang++ used to compile Android-Source-Code is 18.0.1.

Android_15$ ./prebuilts/clang/host/linux-x86/clang-r522817/bin/clang --version
Android (11967740, +pgo, +bolt, +lto, +mlgo, based on r522817) clang version 18.0.1
 (https://android.googlesource.com/toolchain/llvm-project d8003a456d14a3deb8054cdaa529ffbf02d9b262)
Target: x86_64-unknown-linux-gnu
Thread model: posix

3.The gdb used to debug is 9.2:

Android_15$ gdb --version
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04.2) 9.2
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

4.But when I use the default tool-chain clang-18.0.1(prebuilts/clang/host/linux-x86/clang-r522817/bin/clang++), compile a simple hello_world.cpp,
the output ELF a.out can be debug by gdb tool.

Android_15$ ./prebuilts/clang/host/linux-x86/clang-r522817/bin/clang++ hello_world.cpp -g
Android_15$ gdb -tui -args a.out //OK the gdb work correctly.

Below is my file command's output for each ELF file.

1. clang's info:

Android_15$ file  ./prebuilts/clang/host/linux-x86/clang-r522817/bin/clang++
clang++:
ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
statically linked,
Go BuildID=CaRjX2xOY2sn3Eu50jD5/sx0sdGGnrBuwdu7dEfC8/RbpQ82--tce2MQnXDd-h/BpbhCXNCzLlerptoXX1D,
with debug_info,
not stripped

2. malisc_host's info

Android_15$ file ./malisc_host
./malisc_host: 
ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), 
dynamically linked, 
interpreter /lib64/ld-linux-x86-64.so.2, 
for GNU/Linux 2.6.24, 
BuildID[xxHash]=300f2d32f4dbacdf, 
with debug_info, 
not stripped

3. a.out's info:

Android_15$ file ./a.out
a.out info:
ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV),
dynamically linked,
interpreter /lib64/ld-linux-x86-64.so.2,
for GNU/Linux 3.2.0,
with debug_info, 
not stripped

4. gdb's info

Android_15$  file /usr/bin/gdb
/usr/bin/gdb:
ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux),
dynamically linked,
interpreter /lib64/ld-linux-x86-64.so.2,
BuildID[sha1]=f5f8723dbedf08022a36e8449e29e717e6547316,
for GNU/Linux 3.2.0,
stripped

5. readelf ./malisc_host error message .debug_str unsupported compress type: 2

Android_15$ readelf -p .comment ./malisc_host
readelf: Warning: section '.debug_str' has unsupported compress type: 2
String dump of section '.comment':
  [     0]  GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3
  [    2a]  GCC: (GNU) 4.8.3
  [    3c]  Android (11967740, +pgo, +bolt, +lto, +mlgo, based on r522817) clang version 18.0.1 (https://android.googlesource.com/toolchain/llvm-project d8003a456d14a3deb8054cdaa529ffbf02d9b262)
  [    f3]  Linker: LLD 18.0.1

Questions_2

I see the version info between malisc_host and a.out is different.

./clang++          : no version info.
./malisc_host     : for GNU/Linux 2.6.24,
./a.out                : for GNU/Linux 3.2.0,
/usr/bin/gdb     : for GNU/Linux 3.2.0,

Q2.1 Why did the malisc_host's have a different version info?
Q2.2 The malisc_host's version info generated base on what?
Q2.3 Did the "gdb malisc_host: BFD: can not recongize" error message,
caused by the gbd and malisc_host have different version info?
Q2.4 For make clang generate a malisc_host switch it's version from GNU/Linux 2.6.24 to GNU/Linux 3.2.0,
Can we specific a version info for malisc_host,
or we need replace some link-libarary for the malisc_host?

[EugeneZelenko]

Could you please try 20 or main branch? Only most recent release is maintained.

[xiaoqiang-wang]

Hello, @EugeneZelenko @frederick-vs-ja

Thanks for your reply very much.

---

Currently I only can try LLVM-18.0.1 and LLVM-19.0.1,
because the compile tool-chain package can be directly download from Android-Source-Code.

When I try to use LLVM-21.0.0,
I compiled the source code of LLVM-21.0.0 on my computer ,
it generated files missing some binary file, which contained in
clang-18.0.1 (prebuilts/clang/host/linux-x86/clang-r522817/) and
clang-19.0.1 (prebuilts/clang/host/linux-x86/clang-r536225/),
but not generate in LLVM-21.0.0.
for example,

libLLVM.so
libclang_rt.asan-x86_64.a
libclang_rt.builtins-x86_64.a
libclang_rt.ubsan_minimal-x86_64.a
clang_rt.crtbegin-x86_64.o
...
//and many other files

So, I can't use the latest version of LLVM-21.0.0.

---

Q1: Would you kindly give me some guidance on "How to build LLVM-21.0.0 to a Android toolchain package" ?

Q2: Can you give me some hint, How can we analysis this problem on LLVM-18.0.1 and LLVM-19.0.1?

---

---

Does LLVM redefine the ELF's debug_section format?

There is another message, for same malisc_host file,
When I use the Ubuntu's readelf command to get malisc_host's comment section it report a warning,
But the LLVM's llvm-readelf do not report any warning.

1. I use the system default readelf command, it show below warning message,

Android_15$  readelf -p .comment ./malisc_host
readelf: Warning: section '.debug_str' has unsupported compress type: 2

String dump of section '.comment':
  [     0]  GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3
  [    2a]  GCC: (GNU) 4.8.3
  [    3c]  Android (12701618, +pgo, +bolt, +lto, +mlgo, based on r536225) clang version 19.0.1
              (https://android.googlesource.com/toolchain/llvm-project b3a530ec6537146650e42be89f1089e9a3588460)
  [    f3]  Linker: LLD 19.0.1

2. But when I try used the llvm tool-chain llvm-readelf, it not report any warning.

Android_15$  llvm-readelf -p .comment ./malisc_host
String dump of section '.comment':
[     0] GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3
[    2a] GCC: (GNU) 4.8.3
[    3c] Android (12701618, +pgo, +bolt, +lto, +mlgo, based on r536225) clang version 19.0.1
            (https://android.googlesource.com/toolchain/llvm-project b3a530ec6537146650e42be89f1089e9a3588460)
[    f3] Linker: LLD 19.0.1

Q3:Does this means LLVM customize the ELF's debug section,
that lead to gdb can not correctly recognize the malisc_host? How can I fix it?

[xiaoqiang-wang]

Someone told me the solution:
"I think these warnings mean that your gdb & readelf are built without zstd support.
zstd support was added in gdb-13, and the above info says version 12.1, so you need to udpate."

---

Afther I install gdb-13.1, It works well.

Android_15$ gdb_13_1  ./malisc_host  //OK, gdb_13_1 works well.