Messages in this thread | | | Date | Mon, 30 Jan 2023 20:35:03 +0200 | Subject | Re: [PATCH 2/9] perf symbols: Add support for x86 .plt.sec | From | Adrian Hunter <> |
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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)
And what is the distribution?
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