arm - Information about Section Index field (st_shndx) in Section SHT_DYNSYM & SHT_SYMTAB -

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toolchain: product: arm compiler 5.04 component: arm compiler 5.04 update 1 (build 49)

from elf portable formats specification, version 1.1,

section index field (st_shndx) contains: every symbol table entry ‘‘defined’’ in relation section; member holds relevant section header table index.

i compiling simple object (exports 1 global data & routine) understand various fields of elf

source code (test.c):

__declspec(dllexport) int x21 = 0x100; __declspec(dllexport) void bar21(void) {   x21++; }

build script used (build.bat)

armcc -c test.c armlink --bpabi --dll -o test.dll test.o fromelf -cdrsy -o test.txt test.dll

my query usage of st_shndx field of dynsym section & symtab section.

output file (removed few sections keep short)

** section #1 'er_ro' (sht_progbits) [shf_alloc + shf_execinstr]     size   : 24 bytes (alignment 4)     address: 0x00008000      $a     .text     bar21         0x00008000:    e59f000c    ....    ldr      r0,[pc,#12] ; [0x8014] = 0         0x00008004:    e5901000    ....    ldr      r1,[r0,#0]         0x00008008:    e2811001    ....    add      r1,r1,#1         0x0000800c:    e5801000    ....    str      r1,[r0,#0]         0x00008010:    e12fff1e    ../.    bx       lr     $d         0x00008014:    00000000    ....    dcd    0  ** section #2 'er_rw' (sht_progbits) [shf_alloc + shf_write]     size   : 4 bytes (alignment 4)     address: 0x00000000      0x000000:   00 01 00 00                                        ....   ** section #3 '.dynstr' (sht_strtab)     size   : 32 bytes   ** section #4 '.dynsym' (sht_dynsym)     size   : 80 bytes (alignment 4)     string table #3 '.dynstr'     last local symbol no. 1      symbol table .dynsym (4 symbols, 1 local)        #  symbol name                value      bind  sec  type  vis  size     ========================================================================        1  .data                      0x00000000   lc    1  sect  de   0x4       2  shared_2.dll               0x00000000   gb  abs  data  de        3  x21                        0x00000000   gb    1  data  pr   0x4       4  bar21                      0x00008000   gb    2  code  pr   0x14   ** section #5 '.hash' (sht_hash)     size   : 40 bytes (alignment 4)     symbol table #4 '.dynsym' <section truncated>   ** section #7 '.version' (sht_gnu_versym)     size   : 10 bytes (alignment 4)     symbol table #4 '.dynsym' <section truncated>      ** section #8 '.version_d' (sht_gnu_verdef)     size   : 56 bytes (alignment 4)     string table #3 '.dynstr' <section truncated>      ** section #9 '.dynamic' (sht_dynamic)     size   : 120 bytes (alignment 4)     string table #3 '.dynstr' <section truncated>   ** section #10 '.debug_frame' (sht_progbits)     size   : 68 bytes   ** section #11 '.symtab' (sht_symtab)     size   : 176 bytes (alignment 4)     string table #12 '.strtab'     last local symbol no. 6      symbol table .symtab (10 symbols, 6 local)        #  symbol name                value      bind  sec  type  vis  size     ========================================================================        1  $a                         0x00008000   lc    1   --   de        2  $d                         0x00008014   lc    1   --   de        3  $d.realdata                0x00000000   lc    2   --   de        4  shared_2.c                 0x00000000   lc  abs  file  de        5  .text                      0x00008000   lc    1  sect  de        6  .data                      0x00000000   lc    2  sect  de   0x4       7  buildattributes$$arm_isav4$s$pe$a:l22$x:l11$s22$ieee1$~iw$usesv6$~stkckd$usesv7$~shl$ospace$eba8$standardlib$req8$pres8$eabiv2                                     0x00000000   gb  abs   --   hi        8  shared_2.dll               0x00000000   gb  abs  data  de        9  x21                        0x00000000   gb    2  data  pr   0x4      10  bar21                      0x00008000   gb    1  code  pr   0x14

section 1 code area (bar21 routine present here)

section 2 rw area (x21 variable present here)

now, if see st_shndx (section index -- marked "sec" in output above) field in dynsym section & symtab section these 2 variables different.

for example: x21 in dynsym points section 1 (code area) & in symtab, points section 2 (rw area)

can me understand why? or guide me resource can more information on this.

regards, raju udava


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