Messages in this thread | | | From | Namhyung Kim <> | Date | Mon, 30 Jan 2023 09:34:44 -0800 | Subject | Re: [PATCH 2/9] perf symbols: Add support for x86 .plt.sec |
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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
Thanks, Namhyung
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