https://sourceware.org/bugzilla/show_bug.cgi?id=31795
Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:
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CC| |adhemerval.zanella at linaro
dot o
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--- Comment #39 from Adhemerval Zanella <adhemerval.zanella at linaro dot org>
---
(In reply to Fangrui Song from comment #37)
> I agree with mintsuki . The "-pie -Ttext-segment=non-zero => ET_EXEC" hack
> should not be needed.
>
> From https://sourceware.org/pipermail/binutils/2013-December/083381.html
>
> > Linker sets e_type in ELF header to ET_DYN for -pie -Ttext-segment=0xXXX.
> > When I added -Ttext-segment=0xXXX, one goal was to load
> > small model executable above 4GB on Linux/x86-64, which
> > was done with -pie -Ttext-segment=0xXXX. But -pie sets
> > e_type in ELF header to ET_DYN and kernel may ignore
> > p_vaddr in ELF header to load ET_DYN binary at a random
> > address. This patch changes ld to set e_type in ELF header
> > to ET_EXEC if the first PT_LOAD segment has non-zero
> > p_vaddr. If this is unacceptable as generic ELF change,
> > I can make it specific to x86.
>
> Was the intention for the following command to load the text segment at an
> address >= 0x600000000000 ?
>
> ```
> % cat a.c
> #include <stdio.h>
> int main() { printf("%p\n", main); }
> % gcc -pie -Wl,-no-pie a.c -fuse-ld=bfd
> -Wl,--no-relax,-Ttext-segment=0x600000000000 -o a
> % ./a
> 0x600000001139
> % ./a
> 0x600000001139 # no ASLR
> ```
>
> Changing ET_DYN to ET_EXEC fulfills the address requirement but disables
> ASLR.
> Is it intentional?
That's my understanding of reading the -Ttext-segment documentation. The
question is whether we relax the semantic to have it as a minimum address or
define it as the expected address (thus disabling ASLR as a consequence).
I don't have a strong opinion, but currently, Linux only enforces the former (I
think it is the main reason this makes some sense) so we will need to discuss
with kernel developers the expected semantics.
>
> I added `--no-pie` to GNU ld in 2021:
> https://sourceware.org/cgit/binutils-gdb/commit/
> ?id=e8f6c2a5bab10b039a12b69a30a8248c91161e11 , with which we can do the
> following instead. (GNU ld also needs `--no-relax` while lld doesn't).
>
> ```
> % gcc -pie a.c -fuse-ld=bfd
> -Wl,--no-pie,--no-relax,-Ttext-segment=0x600000000000 -o a
> % ./a
> 0x600000001139
> % ./a
> 0x600000001139
> ```
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