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linuxgcccompilationelfreadelf

Why sum of symbol size much less than ".text" section size?

I'm debugging a dynamic shared library in linux, the name of the library is libMNN.so.

Here is the size of all sections of libMNN.so got by size -A ./libMNN.so :

section                  size      addr
.note.gnu.build-id         36       512
.hash                    2288       552
.dynsym                  7368      2840
.dynstr                 11637     10208
.gnu.version              614     21846
.gnu.version_r             64     22464
.rela.dyn               78720     22528
.rela.plt                3960    101248
.plt                     2672    105216
.text                  804416    107904
.rodata                 17772    912320
.eh_frame_hdr           21460    930092
.eh_frame               79160    951552
.note.android.ident       152   1030712
.init_array              1400   1097864
.fini_array                16   1099264
.data.rel.ro            33232   1099280
.dynamic                  560   1132512
.got                     1512   1133072
.data                       8   1134592
.bss                      392   1134608
.comment                  100         0
Total                 1067539

We can see that the size of ".text" is 804416 and the size of ".rodata" is 17772.

Here is the sum of symbol size got by command readelf -D -sW ./libMNN.so | awk '{print $4}' | awk '{s+=$1} END {print s}':

79000

The sum of symbol size is much less than ".text" and ".rodata", why?

libMNN.so can be downloaded from https://github.com/alibaba/MNN/releases/download/1.0.0/Android.zip

Solution

  • LibMNN does not export static, internal and inline functions (by setting their visibility to "hidden") so you do not see symbols for them. Some more space is wasted due to symbol alignments and literal pools (which are stored in .text on ARM).