Why do common C compilers include the source filename in the output?

问题

I have learnt from this recent answer that gcc and clang include the source filename somewhere in the binary as metadata, even when debugging is not enabled.

I can't really understand why this should be a good idea. Besides the tiny privacy risks, this happens also when one optimizes for the size of the resulting binary (-Os), which looks inefficient.

Why do the compilers include this information?

回答1:

The reason why GCC includes the filename is mainly for debugging purposes, because it allows a programmer to identify from which source file a given symbol comes from as (tersely) outlined in the ELF spec p1-17 and further expanded upon in some Oracle docs on linking.

An example of using the STT_FILE section is given by this SO question.

I'm still confused why both GCC and Clang still include it even if you specify -g0, but you can stop it from including STT_FILE with -s. I couldn't find any explanation for this, nor could I find an "official reason" why STT_FILE is included in the ELF specification (which is very terse).

回答2:

I have learnt from this recent answer that gcc includes the source filename somewhere in the binary as metadata, even when debugging is not enabled.

~~Not quite~~. In modern ELF object files the file name indeed is a symbol of type FILE:

$ readelf bignum.o    # Source bignum.c
[...]
Symbol table (.symtab) contains 36 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS bignum.c
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    1
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    3
     4: 0000000000000000     0 SECTION LOCAL  DEFAULT    4
     5: 0000000000000000     0 SECTION LOCAL  DEFAULT    5
     6: 0000000000000000     0 SECTION LOCAL  DEFAULT    6
     7: 0000000000000000     0 SECTION LOCAL  DEFAULT    7
     8: 0000000000000000     0 SECTION LOCAL  DEFAULT    8
     9: 00000000000003f0   172 FUNC    GLOBAL DEFAULT    1 add
    10: 00000000000004a0   104 FUNC    GLOBAL DEFAULT    1 copy

However, once stripped, the symbol is gone:

$ strip bignum.o
$ readelf -all bignum.o | grep bignum.c
$

So to keep your privacy, strip the executable, or compile/link with -s.

来源：https://stackoverflow.com/questions/32413176/why-do-common-c-compilers-include-the-source-filename-in-the-output

标签

gcc

compilation

clang

compiler-optimization

compiler-options