perf symbols: Start adding support for .plt.got for x86

For x86, .plt.got is used, for example, when the address is taken of a
dynamically linked function. Start adding support by synthesizing a
symbol for each entry. A subsequent patch will attempt to get a better
name for the symbol.

Example:

  Before:

    $ cat tstpltlib.c
    void fn1(void) {}
    void fn2(void) {}
    void fn3(void) {}
    void fn4(void) {}
    $ cat tstpltgot.c
    void fn1(void);
    void fn2(void);
    void fn3(void);
    void fn4(void);

    void callfn(void (*fn)(void))
    {
            fn();
    }

    int main()
    {
            fn4();
            fn1();
            callfn(fn3);
            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 tstpltgot tstpltgot.c -L . -ltstpltlib -Wl,-rpath="$(pwd)"
    $ readelf -SW tstpltgot | grep 'Name\|plt\|dyn'
      [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
      [ 6] .dynsym           DYNSYM          00000000000003d8 0003d8 0000f0 18   A  7   1  8
      [ 7] .dynstr           STRTAB          00000000000004c8 0004c8 0000c6 00   A  0   0  1
      [10] .rela.dyn         RELA            00000000000005d8 0005d8 0000d8 18   A  6   0  8
      [11] .rela.plt         RELA            00000000000006b0 0006b0 000048 18  AI  6  24  8
      [13] .plt              PROGBITS        0000000000001020 001020 000040 10  AX  0   0 16
      [14] .plt.got          PROGBITS        0000000000001060 001060 000020 10  AX  0   0 16
      [15] .plt.sec          PROGBITS        0000000000001080 001080 000030 10  AX  0   0 16
      [23] .dynamic          DYNAMIC         0000000000003d90 002d90 000210 10  WA  7   0  8
    $ perf record -e intel_pt//u --filter 'filter main @ ./tstpltgot , filter callfn @ ./tstpltgot' ./tstpltgot
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.011 MB perf.data ]
    $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
    28393.810326915:   tr strt                               0 [unknown] =>     562350baa1b2 main+0x0
    28393.810326915:   tr end  call               562350baa1ba main+0x8 =>     562350baa090 fn4@plt+0x0
    28393.810326917:   tr strt                               0 [unknown] =>     562350baa1bf main+0xd
    28393.810326917:   tr end  call               562350baa1bf main+0xd =>     562350baa080 fn1@plt+0x0
    28393.810326917:   tr strt                               0 [unknown] =>     562350baa1c4 main+0x12
    28393.810326917:   call                       562350baa1ce main+0x1c =>     562350baa199 callfn+0x0
    28393.810326917:   tr end  call               562350baa1ad callfn+0x14 =>     7f607d36110f fn3+0x0
    28393.810326922:   tr strt                               0 [unknown] =>     562350baa1af callfn+0x16
    28393.810326922:   return                     562350baa1b1 callfn+0x18 =>     562350baa1d3 main+0x21
    28393.810326922:   tr end  call               562350baa1d3 main+0x21 =>     562350baa0a0 fn2@plt+0x0
    28393.810326924:   tr strt                               0 [unknown] =>     562350baa1d8 main+0x26
    28393.810326924:   tr end  call               562350baa1d8 main+0x26 =>     562350baa060 [unknown]  <- call to fn3 via .plt.got
    28393.810326925:   tr strt                               0 [unknown] =>     562350baa1dd main+0x2b
    28393.810326925:   tr end  return             562350baa1e3 main+0x31 =>     7f607d029d90 __libc_start_call_main+0x80

  After:

    $ perf script --itrace=be --ns -F+flags,-event,+addr,-period,-comm,-tid,-cpu,-dso
    28393.810326915:   tr strt                               0 [unknown] =>     562350baa1b2 main+0x0
    28393.810326915:   tr end  call               562350baa1ba main+0x8 =>     562350baa090 fn4@plt+0x0
    28393.810326917:   tr strt                               0 [unknown] =>     562350baa1bf main+0xd
    28393.810326917:   tr end  call               562350baa1bf main+0xd =>     562350baa080 fn1@plt+0x0
    28393.810326917:   tr strt                               0 [unknown] =>     562350baa1c4 main+0x12
    28393.810326917:   call                       562350baa1ce main+0x1c =>     562350baa199 callfn+0x0
    28393.810326917:   tr end  call               562350baa1ad callfn+0x14 =>     7f607d36110f fn3+0x0
    28393.810326922:   tr strt                               0 [unknown] =>     562350baa1af callfn+0x16
    28393.810326922:   return                     562350baa1b1 callfn+0x18 =>     562350baa1d3 main+0x21
    28393.810326922:   tr end  call               562350baa1d3 main+0x21 =>     562350baa0a0 fn2@plt+0x0
    28393.810326924:   tr strt                               0 [unknown] =>     562350baa1d8 main+0x26
    28393.810326924:   tr end  call               562350baa1d8 main+0x26 =>     562350baa060 offset_0x1060@plt+0x0
    28393.810326925:   tr strt                               0 [unknown] =>     562350baa1dd main+0x2b
    28393.810326925:   tr end  return             562350baa1e3 main+0x31 =>     7f607d029d90 __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/20230131131625.6964-9-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -466,6 +466,30 @@ static bool machine_is_x86(GElf_Half e_machine)
 	return e_machine == EM_386 || e_machine == EM_X86_64;
 }
 
+static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
+					   GElf_Ehdr *ehdr,
+					   char *buf, size_t buf_sz)
+{
+	struct symbol *sym;
+	GElf_Shdr shdr;
+	Elf_Scn *scn;
+	size_t i;
+
+	scn = elf_section_by_name(elf, ehdr, &shdr, ".plt.got", NULL);
+	if (!scn || !shdr.sh_entsize)
+		return 0;
+
+	for (i = 0; i < shdr.sh_size; i += shdr.sh_entsize) {
+		snprintf(buf, buf_sz, "offset_%#" PRIx64 "@plt", (u64)shdr.sh_offset + i);
+		sym = symbol__new(shdr.sh_offset + i, shdr.sh_entsize, STB_GLOBAL, STT_FUNC, buf);
+		if (!sym)
+			return -1;
+		symbols__insert(&dso->symbols, sym);
+	}
+
+	return 0;
+}
+
 /*
  * 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
@@ -514,6 +538,11 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
 		goto out_elf_end;
 	symbols__insert(&dso->symbols, plt_sym);
 
+	/* Only x86 has .plt.got */
+	if (machine_is_x86(ehdr.e_machine) &&
+	    dso__synthesize_plt_got_symbols(dso, elf, &ehdr, sympltname, sizeof(sympltname)))
+		goto out_elf_end;
+
 	/* Only x86 has .plt.sec */
 	if (machine_is_x86(ehdr.e_machine) &&
 	    elf_section_by_name(elf, &ehdr, &plt_sec_shdr, ".plt.sec", NULL)) {