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
$ perf record -e intel_pt//u --filter 'filter main @ ./tstplt' ./tstplt
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data ]
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
38970.522546686: tr strt 0 [unknown] => 55fc222a81a9 main+0x0
38970.522546686: tr end call 55fc222a81b1 main+0x8 => 55fc222a80a0 [unknown]
38970.522546687: tr strt 0 [unknown] => 55fc222a81b6 main+0xd
38970.522546687: tr end call 55fc222a81b6 main+0xd => 55fc222a8080 [unknown]
38970.522546688: tr strt 0 [unknown] => 55fc222a81bb main+0x12
38970.522546688: tr end call 55fc222a81bb main+0x12 => 55fc222a80b0 [unknown]
38970.522546688: tr strt 0 [unknown] => 55fc222a81c0 main+0x17
38970.522546688: tr end call 55fc222a81c0 main+0x17 => 55fc222a8090 [unknown]
38970.522546689: tr strt 0 [unknown] => 55fc222a81c5 main+0x1c
38970.522546894: tr end return 55fc222a81cb main+0x22 => 7f3a4dc29d90 __libc_start_call_main+0x80
After:
$ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
38970.522546686: tr strt 0 [unknown] => 55fc222a81a9 main+0x0
38970.522546686: tr end call 55fc222a81b1 main+0x8 => 55fc222a80a0 fn4@plt+0x0
38970.522546687: tr strt 0 [unknown] => 55fc222a81b6 main+0xd
38970.522546687: tr end call 55fc222a81b6 main+0xd => 55fc222a8080 fn1@plt+0x0
38970.522546688: tr strt 0 [unknown] => 55fc222a81bb main+0x12
38970.522546688: tr end call 55fc222a81bb main+0x12 => 55fc222a80b0 fn2@plt+0x0
38970.522546688: tr strt 0 [unknown] => 55fc222a81c0 main+0x17
38970.522546688: tr end call 55fc222a81c0 main+0x17 => 55fc222a8090 fn3@plt+0x0
38970.522546689: tr strt 0 [unknown] => 55fc222a81c5 main+0x1c
38970.522546894: tr end return 55fc222a81cb main+0x22 => 7f3a4dc29d90 __libc_start_call_main+0x80
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 30 +++++++++++++++++++++++-------
1 file changed, 23 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 9328c162d68f..bb1b5cb3ff12 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -379,6 +379,11 @@ static bool get_plt_sizes(struct dso *dso, GElf_Ehdr *ehdr, GElf_Shdr *shdr_plt,
return false;
}
+static bool machine_is_x86(GElf_Half e_machine)
+{
+ return e_machine == EM_386 || e_machine == EM_X86_64;
+}
+
/*
* We need to check if we have a .dynsym, so that we can handle the
* .plt, synthesizing its symbols, that aren't on the symtabs (be it
@@ -391,8 +396,8 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
uint32_t nr_rel_entries, idx;
GElf_Sym sym;
u64 plt_offset, plt_header_size, plt_entry_size;
- GElf_Shdr shdr_plt;
- struct symbol *f;
+ GElf_Shdr shdr_plt, plt_sec_shdr;
+ struct symbol *f, *plt_sym;
GElf_Shdr shdr_rel_plt, shdr_dynsym;
Elf_Data *syms, *symstrs;
Elf_Scn *scn_plt_rel, *scn_symstrs, *scn_dynsym;
@@ -422,10 +427,23 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
return 0;
/* Add a symbol for .plt header */
- f = symbol__new(shdr_plt.sh_offset, plt_header_size, STB_GLOBAL, STT_FUNC, ".plt");
- if (!f)
+ plt_sym = symbol__new(shdr_plt.sh_offset, plt_header_size, STB_GLOBAL, STT_FUNC, ".plt");
+ if (!plt_sym)
goto out_elf_end;
- symbols__insert(&dso->symbols, f);
+ symbols__insert(&dso->symbols, plt_sym);
+
+ /* Only x86 has .plt.sec */
+ if (machine_is_x86(ehdr.e_machine) &&
+ elf_section_by_name(elf, &ehdr, &plt_sec_shdr, ".plt.sec", NULL)) {
+ if (!get_plt_sizes(dso, &ehdr, &plt_sec_shdr, &plt_header_size, &plt_entry_size))
+ return 0;
+ /* Extend .plt symbol to entire .plt */
+ plt_sym->end = plt_sym->start + shdr_plt.sh_size;
+ /* Use .plt.sec offset */
+ plt_offset = plt_sec_shdr.sh_offset;
+ } else {
+ plt_offset = shdr_plt.sh_offset + plt_header_size;
+ }
scn_dynsym = ss->dynsym;
shdr_dynsym = ss->dynshdr;
@@ -474,8 +492,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
goto out_elf_end;
nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
- plt_offset = shdr_plt.sh_offset;
- plt_offset += plt_header_size;
ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;
--
2.34.1Hi 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
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?
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.
Thanks,
Namhyung
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.
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