Re: gcc behavior of init priority of .ctors and .dtors section

On Thu, May 16, 2024 at 08:05:57PM +0000, Lorenzo Salvadore wrote:
> On Thursday, May 16th, 2024 at 20:26, Konstantin Belousov <kostikbel@gmail.com> wrote:
> > > gcc13 from ports
> > > `# gcc ctors.c && ./a.out init 1 init 2 init 5 init 4 init 3 main fini 3 fini 4 fini 5 fini 2 fini 1`
> > > 
> > > The above order is not expected. I think clang's one is correct.
> > > 
> > > Further hacking with readelf shows that clang produces the right order of
> > > section .rela.ctors but gcc does not.
> > > 
> > > ```
> > > # clang -fno-use-init-array -c ctors.c && readelf -r ctors.o | grep 'Relocation section with addend (.rela.ctors)' -A5 > clang.txt
> > > # gcc -c ctors.c && readelf -r ctors.o | grep 'Relocation section with addend (.rela.ctors)' -A5 > gcc.txt
> > > # diff clang.txt gcc.txt
> > > 3,5c3,5
> > > < 000000000000 000800000001 R_X86_64_64 0000000000000060 init_65535_2 + 0
> > > < 000000000008 000700000001 R_X86_64_64 0000000000000040 init + 0
> > > < 000000000010 000600000001 R_X86_64_64 0000000000000020 init_65535 + 0
> > > ---
> > > 
> > > > 000000000000 000600000001 R_X86_64_64 0000000000000011 init_65535 + 0
> > > > 000000000008 000700000001 R_X86_64_64 0000000000000022 init + 0
> > > > 000000000010 000800000001 R_X86_64_64 0000000000000033 init_65535_2 + 0
> > > > ```
> > > 
> > > The above show clearly gcc produces the wrong order of section `.rela.ctors`.
> > > 
> > > Is that expected behavior ?
> > > 
> > > I have not tried Linux version of gcc.
> > 
> > Note that init array vs. init function behavior is encoded by a note added
> > by crt1.o. I suspect that the problem is that gcc port is built without
> > --enable-initfini-array configure option.
> 
> Indeed, support for .init_array and .fini_array has been added to the GCC ports
> but is present in the *-devel ports only for now. I will
> soon proceed to enable it for the GCC standard ports too. lang/gcc14 is soon
> to be added to the ports tree and will have it since the beginning.
It is not 'support', but a bug.  For very long time, crt1.o instructs rtld
to use initarray instead of initfunc.  gcc generates broken binaries trying
to use initfunc.

> 
> If this is indeed the issue, switching to a -devel GCC port should fix it.
> 
> Cheers,
> 
> Lorenzo Salvadore