[llvm-dev] clang is not emitting .ARM.extab section?

[kamlesh kumar via llvm-dev]

Hi Devs,

For the below sample :

$cat test.cpp
int foo();
int main(){
int f=foo();
return 0;
}

We  compiled with clang(8.1) like

$clang -fno-builtin --target=arm-eabi  -mabi=aapcs -mlittle-endian
-mfpu=vfpv3 -mfloat-abi=hard -mcpu=cortex-a9 -O0 test.cpp -c

$readelfarm -S test.o
Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk
Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0
 0  0
  [ 1] .strtab           STRTAB          00000000 0001e8 000085 00      0
 0  1
  [ 2] .text             PROGBITS        00000000 000034 00002c 00  AX  0
 0  4
  [ 3] .rel.text         REL             00000000 0001d0 000008 08      9
 2  4
  [ 4] .ARM.exidx        ARM_EXIDX       00000000 000060 000008 00  AL  2
 0  4
  [ 5] .rel.ARM.exidx    REL             00000000 0001d8 000010 08      9
 4  4
  [ 6] .comment          PROGBITS        00000000 000068 0000ac 01  MS  0
 0  1
  [ 7] .note.GNU-stack   PROGBITS        00000000 000114 000000 00      0
 0  1
  [ 8] .ARM.attributes   ARM_ATTRIBUTES  00000000 000114 000049 00      0
 0  1
  [ 9] .symtab           SYMTAB          00000000 000160 000070 10      1
 4  4

And compiled by gcc:
$gcc  -fno-builtin -mabi=aapcs -mlittle-endian -mfpu=vfpv3 -mfloat-abi=hard
-mcpu=cortex-a9 -O0 test.cpp -c

$readelf -S test.o
Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk
Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0
 0  0
  [ 1] .text             PROGBITS        00000000 000034 000028 00  AX  0
 0  4
  [ 2] .rel.text         REL             00000000 00025c 000008 08   I 12
 1  4
  [ 3] .data             PROGBITS        00000000 00005c 000000 00  WA  0
 0  1
  [ 4] .bss              NOBITS          00000000 00005c 000000 00  WA  0
 0  1
  [ 5] .ARM.extab        PROGBITS        00000000 00005c 00000c 00   A  0
 0  4
  [ 6] .ARM.exidx        ARM_EXIDX       00000000 000068 000008 00  AL  1
 0  4
  [ 7] .rel.ARM.exidx    REL             00000000 000264 000018 08   I 12
 6  4
  [ 8] .comment          PROGBITS        00000000 000070 000012 01  MS  0
 0  1
  [ 9] .note.GNU-stack   PROGBITS        00000000 000082 000000 00      0
 0  1
  [10] .ARM.attributes   ARM_ATTRIBUTES  00000000 000082 000033 00      0
 0  1
  [11] .shstrtab         STRTAB          00000000 0000b5 000073 00      0
 0  1
  [12] .symtab           SYMTAB          00000000 000128 000100 10     13
13  4
  [13] .strtab           STRTAB          00000000 000228 000034 00      0
 0  1

>From the above sections you see that .ARM.extab  and  .ARM.exidx sections
are emitted by gcc  and in-case of clang only  the .ARM.exidx  section is
present.

We tried with -funwind-tables option too for clang with no luck and  we are
going with ARM EHABI  to understand these sections better, meanwhile  .

Is that  the clang semantics(not emitting the .ARM.extab section )  is
expected ?

~Kamlesh
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