[LLVMdev] [lld] Handling multiple -init/-fini command line options

[Will Newton]

On 8 December 2014 at 16:21, Shankar Easwaran <shankare at codeaurora.org> wrote:
> This is a bug with the Gnu linker, IMO. There is also some behavioral
> difference for static executables when the -init/-fini options are used too.
>
> The DT_INIT/DT_FINI correspond to one initializer function,where as
> DT_INIT_ARRAY/DT_FINI_ARRAY is used when there is more than one initalizer
> function/finalizer function respectively.
>
> You could ask this same question in the binutils forums, but I think we
> should use DT_INIT_ARRAY/DT_FINI_ARRAY if more than one init/fini function
> is supplied by the user.

One reason why this behaviour is useful in the GNU world is if the
compiler adds an -init flag then the user can add
CFLAGS="-Wl,-init,foo" and override what the compiler passes without
causing an error. How useful this is in this particular case I am not
sure but it holds true for some linker options.

> On 12/8/2014 12:22 AM, Simon Atanasyan wrote:
>>
>> Hi,
>>
>> The LLD linker in gnu flavor mode accepts multiple -init/-fini command
>> line options. For _all_ symbols specified by these options the linker
>> creates appropriate entries in the .init_array/.fini_array sections.
>> But it looks like LD and Gold linkers do not support this feature and
>> take in account only the last -init/-fini options.
>>
>> % cat foo.c
>> int a = 0;
>> void foo() { a += 1; }
>> void bar() { a += 2; }
>>
>> % cat main.c
>> extern int a;
>> int printf(const char *, ...);
>> int main() { printf("a: %d\n", a); }
>>
>> % gcc -fPIC -shared -o libfoo.so -Wl,-init,foo -Wl,-init,bar foo.c
>> % gcc main.c -L. -lfoo -Wl,-rpath,.
>> % ./a.out
>> 2
>>
>> % gcc -fPIC -shared -o libfoo.so -Wl,-init,bar -Wl,-init,foo foo.c
>> % ./a.out
>> 1
>>
>> What is the reason of this incompatibility? The question is caused by
>> attempt to support DT_INIT/DT_FINI dynamic table tags. The table can
>> contain no more than one DT_INIT/DT_FINI tags. The LD and Gold linker
>> look up either default symbols (_init/_fini) or symbols specified by
>> the -init/-fini options and put their values to the tags.
>>
>
>
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-- 
Will Newton
Toolchain Working Group, Linaro