Re: [PATCH 2/9] perf symbols: Add support for x86 .plt.sec

Adrian Hunter
2023-01-31T10:14:45Z

On 31/01/23 00:22, Namhyung Kim wrote:
> On Mon, Jan 30, 2023 at 10:35 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> On 30/01/23 19:34, Namhyung Kim wrote:
>>> Hi Adrian,
>>>
>>> On Fri, Jan 27, 2023 at 9:02 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>>
>>>> The section .plt.sec was originally added for MPX and was first called
>>>> .plt.bnd. While MPX has been deprecated, .plt.sec is now also used for IBT.
>>>> On x86_64, IBT seems to be enabled by default, but can be switched off
>>>> using gcc option -fcf-protection=none. On 32-bit, option -z ibt will
>>>> enable IBT.
>>>>
>>>> With .plt.sec, calls are made into .plt.sec instead of .plt, so it
>>>> makes more sense to put the symbols there instead of .plt. A notable
>>>> difference is that .plt.sec does not have a header entry.
>>>>
>>>> For x86, when synthesizing symbols for plt, use offset and entry size of
>>>> .plt.sec instead of .plt when there is a .plt.sec section.
>>>>
>>>> Example on Ubuntu 22.04 gcc 11.3:
>>>>
>>>> Before:
>>>>
>>>> $ cat tstpltlib.c
>>>> void fn1(void) {}
>>>> void fn2(void) {}
>>>> void fn3(void) {}
>>>> void fn4(void) {}
>>>> $ cat tstplt.c
>>>> void fn1(void);
>>>> void fn2(void);
>>>> void fn3(void);
>>>> void fn4(void);
>>>>
>>>> int main()
>>>> {
>>>> fn4();
>>>> fn1();
>>>> fn2();
>>>> fn3();
>>>> return 0;
>>>> }
>>>> $ gcc --version
>>>> gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
>>>> Copyright (C) 2021 Free Software Foundation, Inc.
>>>> This is free software; see the source for copying conditions. There is NO
>>>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>>> $ gcc -Wall -Wextra -shared -o libtstpltlib.so tstpltlib.c
>>>> $ gcc -Wall -Wextra -o tstplt tstplt.c -L . -ltstpltlib -Wl,-rpath=$(pwd)
>>>> $ readelf -SW tstplt | grep 'plt\|Name'
>>>> [Nr] Name Type Address Off Size ES Flg Lk Inf Al
>>>> [11] .rela.plt RELA 0000000000000698 000698 000060 18 AI 6 24 8
>>>> [13] .plt PROGBITS 0000000000001020 001020 000050 10 AX 0 0 16
>>>> [14] .plt.got PROGBITS 0000000000001070 001070 000010 10 AX 0 0 16
>>>> [15] .plt.sec PROGBITS 0000000000001080 001080 000040 10 AX 0 0 16
>>>
>>> On my machine, it's not enabled by default. And it doesn't create .plt.sec
>>> even if I pass -fcf-protection=full option.
>>>
>>> $ gcc --version
>>> gcc (Debian 12.2.0-10) 12.2.0
>>> Copyright (C) 2022 Free Software Foundation, Inc.
>>> This is free software; see the source for copying conditions. There is NO
>>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>>
>>> $ gcc -Wall -Wextra -shared -fcf-protection=full -o libtstplt.so tstpltlib.c
>>> $ gcc -Wall -Wextra -fcf-protection=full -o tstplt tstplt.c -L.
>>> -ltstpltlib -Wl,-rpath,$(pwd)
>>> $ readelf -SW tstplt | grep 'plt\|Name'
>>> [Nr] Name Type Address Off Size
>>> ES Flg Lk Inf Al
>>> [11] .rela.plt RELA 0000000000000688 000688
>>> 000060 18 AI 6 24 8
>>> [13] .plt PROGBITS 0000000000001020 001020
>>> 000050 10 AX 0 0 16
>>> [14] .plt.got PROGBITS 0000000000001070 001070
>>> 000008 08 AX 0 0 8
>>> [24] .got.plt PROGBITS 0000000000003fe8 002fe8
>>> 000038 08 WA 0 0 8
>>
>> That is interesting. What does it say with -v i.e.
>>
>> gcc -v -Wall -Wextra -o tstplt tstplt.c -L . -ltstpltlib -Wl,-rpath=$(pwd)
>
> Using built-in specs.
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
> OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
> OFFLOAD_TARGET_DEFAULT=1
> Target: x86_64-linux-gnu
> Configured with: ../src/configure -v --with-pkgversion='Debian
> 12.2.0-10' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
> --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2
> --prefix=/usr --with-gcc-major-version-only --program-suffix=-12
> --program-prefix=x86_64-linux-gnu- --enable-shared
> --enable-linker-build-id --libexecdir=/usr/lib
> --without-included-gettext --enable-threads=posix --libdir=/usr/lib
> --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
> --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
> --enable-gnu-unique-object --disable-vtable-verify --enable-plugin
> --enable-default-pie --with-system-zlib
> --enable-libphobos-checking=release --with-target-system-zlib=auto
> --enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
> --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
> --enable-multilib --with-tune=generic
> --enable-offload-targets=nvptx-none=/build/gcc-12-hWCYKv/gcc-12-12.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-hWCYKv/gcc-12-12.2.0/debian/tmp-gcn/usr
> --enable-offload-defaulted --without-cuda-driver
> --enable-checking=release --build=x86_64-linux-gnu
> --host=x86_64-linux-gnu --target=x86_64-linux-gnu
> Thread model: posix
> Supported LTO compression algorithms: zlib zstd
> gcc version 12.2.0 (Debian 12.2.0-10)
> COLLECT_GCC_OPTIONS='-Wall' '-Wextra' '-fcf-protection=full' '-v' '-o'
> 'tstplt' '-L.' '-mtune=generic' '-march=x86-64' '-dumpdir' 'tstplt-'
> /usr/lib/gcc/x86_64-linux-gnu/12/cc1 -quiet -v -imultiarch
> x86_64-linux-gnu tstplt.c -quiet -dumpdir tstplt- -dumpbase tstplt.c
> -dumpbase-ext .c -mtune=generic -march=x86-64 -Wall -Wextra -version
> -fcf-protection=full -fasynchronous-unwind-tables -o /tmp/ccKPWeTD.s
> GNU C17 (Debian 12.2.0-10) version 12.2.0 (x86_64-linux-gnu)
> compiled by GNU C version 12.2.0, GMP version 6.2.1, MPFR version
> 4.1.0, MPC version 1.2.1, isl version isl-0.25-GMP
>
> GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
> ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
> ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/12/include-fixed"
> ignoring nonexistent directory
> "/usr/lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include"
> #include "..." search starts here:
> #include <...> search starts here:
> /usr/lib/gcc/x86_64-linux-gnu/12/include
> /usr/local/include
> /usr/include/x86_64-linux-gnu
> /usr/include
> End of search list.
> GNU C17 (Debian 12.2.0-10) version 12.2.0 (x86_64-linux-gnu)
> compiled by GNU C version 12.2.0, GMP version 6.2.1, MPFR version
> 4.1.0, MPC version 1.2.1, isl version isl-0.25-GMP
>
> GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
> Compiler executable checksum: 0bf64a455b69fb48d1b44a013a099136
> COLLECT_GCC_OPTIONS='-Wall' '-Wextra' '-fcf-protection=full' '-v' '-o'
> 'tstplt' '-L.' '-mtune=generic' '-march=x86-64' '-dumpdir' 'tstplt-'
> as -v --64 -o /tmp/cc0IMyNr.o /tmp/ccKPWeTD.s
> GNU assembler version 2.39.50 (x86_64-linux-gnu) using BFD version
> (GNU Binutils for Debian) 2.39.50.20221208
> COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/
> LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../:/lib/:/usr/lib/
> COLLECT_GCC_OPTIONS='-Wall' '-Wextra' '-fcf-protection=full' '-v' '-o'
> 'tstplt' '-L.' '-mtune=generic' '-march=x86-64' '-dumpdir' 'tstplt.'
> /usr/lib/gcc/x86_64-linux-gnu/12/collect2 -plugin
> /usr/lib/gcc/x86_64-linux-gnu/12/liblto_plugin.so
> -plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
> -plugin-opt=-fresolution=/tmp/ccU2c2jz.res
> -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s
> -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc
> -plugin-opt=-pass-through=-lgcc_s --build-id --eh-frame-hdr -m
> elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker
> /lib64/ld-linux-x86-64.so.2 -pie -o tstplt
> /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/Scrt1.o
> /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/crti.o
> /usr/lib/gcc/x86_64-linux-gnu/12/crtbeginS.o -L.
> -L/usr/lib/gcc/x86_64-linux-gnu/12
> -L/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu
> -L/usr/lib/gcc/x86_64-linux-gnu/12/../../../../lib
> -L/lib/x86_64-linux-gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu
> -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/12/../../..
> /tmp/cc0IMyNr.o -ltstpltlib -rpath=/home/namhyung/tmp/plt-test -lgcc
> --push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state
> --as-needed -lgcc_s --pop-state
> /usr/lib/gcc/x86_64-linux-gnu/12/crtendS.o
> /usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/crtn.o
> COLLECT_GCC_OPTIONS='-Wall' '-Wextra' '-fcf-protection=full' '-v' '-o'
> 'tstplt' '-L.' '-mtune=generic' '-march=x86-64' '-dumpdir' 'tstplt.'
>
>
>>
>> And what is the distribution?
>
> It's a Debian (Testing) with some customization.

Seems to need also options -z ibt and/or -z ibtplt

I will send a V2 with updated examples.