[llvm-dev] Debugging LowerTypeTests in LLVM Using GDB

[Shishir V Jessu via llvm-dev]

Hi Yuanfang,

Do you have any guidance about how to proceed from here? The following is
the output from the command you've given:

"Target: x86_64-unknown-linux-gnuThread model: posixInstalledDir:
/home/shishir_jessu/clang/build/bin/.
"/home/shishir_jessu/clang/build/bin/clang-10" "-cc1" "-triple"
"x86_64-unknown-linux-gnu" "-emit-llvm-bc" "-flto" "-flto-unit"
"-disable-free" "-main-file-name" "indirect.c" "-mrelocation-model"
"static" "-mthread-model" "posix" "-mframe-pointer=all" "-fmath-errno"
"-masm-verbose" "-mconstructor-aliases" "-munwind-tables"
"-fuse-init-array" "-target-cpu" "x86-64" "-dwarf-column-info"
"-debugger-tuning=gdb" "-resource-dir"
"/home/shishir_jessu/clang/build/lib/clang/10.0.0" "-internal-isystem"
"/usr/local/include" "-internal-isystem"
"/home/shishir_jessu/clang/build/lib/clang/10.0.0/include"
"-internal-externc-isystem" "/usr/include/x86_64-linux-gnu"
"-internal-externc-isystem" "/include" "-internal-externc-isystem"
"/usr/include" "-fdebug-compilation-dir"
"/home/shishir_jessu/clang/build/bin" "-ferror-limit" "19"
"-fmessage-length" "0" "-fsanitize=cfi-icall"
"-fsanitize-trap=cfi-icall"
"-fsanitize-blacklist=/home/shishir_jessu/clang/build/lib/clang/10.0.0/share/cfi_blacklist.txt"
"-fsanitize-cfi-canonical-jump-tables" "-fobjc-runtime=gcc"
"-fdiagnostics-show-option" "-fcolor-diagnostics" "-fsplit-lto-unit"
"-faddrsig" "-o" "/tmp/indirect-1aceda.o" "-x" "c" "indirect.c"
"/usr/bin/ld" "-z" "relro" "--hash-style=gnu" "--eh-frame-hdr" "-m"
"elf_x86_64" "-dynamic-linker" "/lib64/ld-linux-x86-64.so.2" "-o"
"indirect" "/usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../x86_64-linux-gnu/crt1.o"
"/usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../x86_64-linux-gnu/crti.o"
"/usr/lib/gcc/x86_64-linux-gnu/7.4.0/crtbegin.o"
"-L/usr/lib/gcc/x86_64-linux-gnu/7.4.0"
"-L/usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../x86_64-linux-gnu"
"-L/lib/x86_64-linux-gnu" "-L/lib/../lib64"
"-L/usr/lib/x86_64-linux-gnu"
"-L/usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../.."
"-L/home/shishir_jessu/clang/build/bin/../lib" "-L/lib" "-L/usr/lib"
"-plugin" "/home/shishir_jessu/clang/build/bin/../lib/LLVMgold.so"
"-plugin-opt=mcpu=x86-64" "/tmp/indirect-1aceda.o" "-lgcc"
"--as-needed" "-lgcc_s" "--no-as-needed" "-lc" "-lgcc" "--as-needed"
"-lgcc_s" "--no-as-needed"
"/usr/lib/gcc/x86_64-linux-gnu/7.4.0/crtend.o"
"/usr/lib/gcc/x86_64-linux-gnu/7.4.0/../../../x86_64-linux-gnu/crtn.o"


Of the flags given, I only need one of them. So I run clang -cc1 -fsanitize=
cfi-icall indirect.c,  but am still not able to hit the code I'm looking
for. Is there anything else I should be doing? Thank you!

Shishir Jessu

On Mon, Sep 30, 2019 at 2:55 PM <Yuanfang.Chen at sony.com> wrote:

> `clang` is the driver not the compiler.
>
>
>
> Run this to get the compiler invocation: (“path/to/clang” “-cc1” ….), then
> debug that instead.
>
> "clang -flto -fsanitize=cfi-icall indirect.c -o indirect -###"
>
>
>
> -Yuanfang
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Shishir
> V Jessu via llvm-dev
> *Sent:* Monday, September 30, 2019 12:42 PM
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] Debugging LowerTypeTests in LLVM Using GDB
>
>
>
> Hi,
>
> I am looking into Control-Flow Integrity for indirect function calls,
> implemented with jump tables. I want to step through the code that produces
> these jump tables in GDB. I have built clang and opt from source with
> debugging symbols. I believe this code lives in
> llvm/lib/Transforms/LowerTypeTests.cpp, but when I try to debug *opt* by
> running the command "run -lowertypetests cfi-icall.bc > /dev/null", I am
> never able to reach this file.
>
> Also, I have tried to debug the command "clang -flto -fsanitize=cfi-icall
> indirect.c -o indirect" (where indirect.c is a C file containing an
> indirect call), and am able to see the CFI jump tables in the resulting
> assembly, but I cannot reach the code that produces these jump tables in
> GDB. Am I targeting the wrong code for these changes, or is there something
> more I need in order to run through this code in GDB? Thanks for your help!
>
> Shishir Jessu
>
>
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