perf symbols: Add support for x86 .plt.sec

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 may be enabled by default, but can be switched off
using gcc option -fcf-protection=none, or switched on by -z ibt or -z
ibtplt. On 32-bit, option -z ibt or -z ibtplt 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 -z ibt -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
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230131131625.6964-3-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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;