record: Library functions not traced

[clementguidi]

Hey,

On my machine (Oracle 7 x86_64 GCC-6.3), f7ecadb breaks test 001 basic and many more. getpid() is missing from the output (see below).

Is that related to entry size?

Compiler                  gc
Runtime test case         pg
------------------------: O0
build command: gcc -o t-abc -fno-inline -fno-builtin -fno-ipa-cp -fno-omit-frame-pointer -D_FORTIFY_SOURCE=0  -pg -O0 -fno-ipa-sra  s-abc.c
test command: /localdisk/uftrace/uftrace live --no-pager --no-event --libmcount-path=/localdisk/uftrace   -N memcpy t-abc
=========== original ===========
# DURATION     TID     FUNCTION
            [ 25525] | main() {
            [ 25525] |   a() {
            [ 25525] |     b() {
   0.629 us [ 25525] |       c();
   1.889 us [ 25525] |     } /* b */
   2.242 us [ 25525] |   } /* a */
   3.181 us [ 25525] | } /* main */

===========  result  ===========
main() {
   a() {
     b() {
       c();
     } /* b */
   } /* a */
 } /* main */
=========== expected ===========
main() {
   a() {
     b() {
       c() {
         getpid();
       } /* c */
     } /* b */
   } /* a */
 } /* main */
001 basic               : NG

[namhyung]

Probably. Can you please run the test program (or anything simple) with -v option? And also please share the output of readelf -SW <your-binary>.

[clementguidi]

Right, I spotted the plthook: cannot find REL(A)ENT size line.
I'm using tests/s-abc.c as source.

$ gcc -o t-abc -fno-inline -fno-builtin -fno-ipa-cp -fno-omit-frame-pointer -D_FORTIFY_SOURCE=0  -pg -O0 -fno-ipa-sra  s-abc.c
$ uftrace -v t-abc
uftrace: running uftrace v0.14-97-gf7ec ( x86_64 dwarf python3 tui perf sched dynamic )
uftrace: checking binary t-abc
uftrace: using /usr/local/lib/uftrace/libmcount.so library for tracing
uftrace: creating 3 thread(s) for recording
mcount: initializing mcount library
plthook: setup PLT hooking "/localdisk/uftrace/tests/t-abc"
plthook: cannot find REL(A)ENT size
mcount: mcount setup done
mcount: new session started: d1d99009924f59b3: t-abc
mcount: mcount trace finished
mcount: exit from libmcount
uftrace: child terminated with exit code: 0
uftrace: cannot read build-id section
uftrace: reading /tmp/uftrace-live-OTKMLH/task.txt file
uftrace: flushing /uftrace-d1d99009924f59b3-27908-000
uftrace: live-record finished..
uftrace: start live-replaying...
uftrace: reading /tmp/uftrace-live-OTKMLH/task.txt file
fstack: fixup for some special functions
uftrace: add field "duration"
uftrace: add field "tid"
# DURATION     TID     FUNCTION
            [ 27908] | main() {
            [ 27908] |   a() {
            [ 27908] |     b() {
   0.530 us [ 27908] |       c();
   1.993 us [ 27908] |     } /* b */
   2.357 us [ 27908] |   } /* a */
   3.267 us [ 27908] | } /* main */
uftrace: removing /tmp/uftrace-live-OTKMLH directory

$ readelf -SW t-abc
There are 27 section headers, starting at offset 0x1ab8:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .interp           PROGBITS        0000000000400238 000238 00001c 00   A  0   0  1
  [ 2] .note.ABI-tag     NOTE            0000000000400254 000254 000020 00   A  0   0  4
  [ 3] .hash             HASH            0000000000400278 000278 000034 04   A  4   0  8
  [ 4] .dynsym           DYNSYM          00000000004002b0 0002b0 0000c0 18   A  5   1  8
  [ 5] .dynstr           STRTAB          0000000000400370 000370 000060 00   A  0   0  1
  [ 6] .gnu.version      VERSYM          00000000004003d0 0003d0 000010 02   A  4   0  2
  [ 7] .gnu.version_r    VERNEED         00000000004003e0 0003e0 000020 00   A  5   1  8
  [ 8] .rela.plt         RELA            0000000000400400 000400 0000a8 18  AI  4  20  8
  [ 9] .init             PROGBITS        00000000004004a8 0004a8 00001a 00  AX  0   0  4
  [10] .plt              PROGBITS        00000000004004d0 0004d0 000080 10  AX  0   0 16
  [11] .text             PROGBITS        0000000000400550 000550 00027c 00  AX  0   0 16
  [12] .fini             PROGBITS        00000000004007cc 0007cc 000009 00  AX  0   0  4
  [13] .rodata           PROGBITS        00000000004007d8 0007d8 000004 04  AM  0   0  4
  [14] .eh_frame_hdr     PROGBITS        00000000004007dc 0007dc 00005c 00   A  0   0  4
  [15] .eh_frame         PROGBITS        0000000000400838 000838 000184 00   A  0   0  8
  [16] .init_array       INIT_ARRAY      0000000000600e48 000e48 000008 08  WA  0   0  8
  [17] .fini_array       FINI_ARRAY      0000000000600e50 000e50 000008 08  WA  0   0  8
  [18] .jcr              PROGBITS        0000000000600e58 000e58 000008 00  WA  0   0  8
  [19] .dynamic          DYNAMIC         0000000000600e60 000e60 0001a0 10  WA  5   0  8
  [20] .got.plt          PROGBITS        0000000000601000 001000 000050 08  WA  0   0  8
  [21] .data             PROGBITS        0000000000601050 001050 000010 00  WA  0   0  8
  [22] .bss              NOBITS          0000000000601060 001060 000008 00  WA  0   0 16
  [23] .comment          PROGBITS        0000000000000000 001060 000042 01  MS  0   0  1
  [24] .symtab           SYMTAB          0000000000000000 0010a8 0006c0 18     25  48  8
  [25] .strtab           STRTAB          0000000000000000 001768 00026e 00      0   0  1
  [26] .shstrtab         STRTAB          0000000000000000 0019d6 0000e2 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  l (large), p (processor specific)

[namhyung]

Ok, it seems the dynamic section doesn't have the data. But the section header (.rela.plt) has the entry size so we can fallback to read it.

[namhyung]

How about this?

diff --git a/libmcount/plthook.c b/libmcount/plthook.c
index 59f8e00b..bbc9c433 100644
--- a/libmcount/plthook.c
+++ b/libmcount/plthook.c
@@ -246,8 +246,22 @@ static int find_got(struct uftrace_elf_data *elf, struct uftrace_elf_iter *iter,
        }
 
        if (jmprel_ent_size == 0) {
-               pr_dbg("cannot find REL(A)ENT size\n");
-               return 0;
+               /*
+                * Some compilers didn't generate DT_REL(A)ENT entry.
+                * Check the section header for the entry size.
+                */
+               elf_for_each_shdr(elf, &sec_iter) {
+                       if (sec_iter.shdr.sh_type == SHT_REL ||
+                           sec_iter.shdr.sh_type == SHT_RELA) {
+                               jmprel_ent_size = sec_iter.shdr.sh_entsize;
+                               break;
+                       }
+               }
+
+               if (jmprel_ent_size == 0) {
+                       pr_dbg("cannot find REL(A)ENT size\n");
+                       return 0;
+               }
        }
 
        elf_for_each_shdr(elf, &sec_iter) {

[clementguidi]

That solves the problem on my machine. Thank you.