puzzles about hidden_def and hidden_proto

[Ken YANG <spng.yang@gmail.com>]

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hi all,

i have three puzzles about the macro "hidden_def"
and "hidden_proto" in "libsepol/src/dso.h".

i copy the definitions of these two macros into
a separate header file to test these two macros,
and assembly them:

$ cat hidden_def.h

int extern_i=12345;
#define hidden __attribute__ ((visibility("hidden")))
#define hidden_proto(fct) __hidden_proto (fct, fct##_internal)
#define __hidden_proto(fct, internal)   \
        extern __typeof(fct) internal;  \
        extern __typeof(fct) fct __asm (#internal) hidden;
#define hidden_def(fct) \
        asm (".globl " #fct "\n.set " #fct ", " #fct "_internal");

$ cat hidden_def.c

#include "hidden_def.h"
int main()
{
        hidden_proto(extern_i);
}

$ gcc -S hidden_def.c -o hidden_proto.s
hidden_def.c: In function ¡®main¡¯:
hidden_def.c:17: warning: asm declaration ignored due to conflict with
previous rename

as a result, there aren't #APP(#NO_APP) section in ".s" file

Questions:

(1)
i don't know why i got these assembly warning?

(2)
i find in the gas manual:

.set SYMBOL, EXPRESSION

if SYMBOL are flagged as external, it remains flagged

how can "fct" be hidden, because it has been declared as globl.

(3)
what is the difference between hidden_def and gcc hidden
visibility attribute? why libsepol use both of them?


i know these problems are not selinux-specific, but i have
googled for a long time, i don't know where i can get guides
about these kinds of problems. can anyone give me some hints?






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