https://sourceware.org/bugzilla/show_bug.cgi?id=31795
--- Comment #41 from mintsuki <mintsuki at protonmail dot com> --- (In reply to Adhemerval Zanella from comment #39) > (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). My understanding is that the PT_LOAD PHDR addresses could be slid, as long as they are slid above the specified address. The fact that the first PT_LOAD PHDR is 0 or not should be irrelevant. It makes no sense for it to be relevant, let alone for it to dictate the ELF type to be ET_EXEC. This is how Limine behaves, and how I interpret the ELF format. > > 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 > > ``` -- You are receiving this mail because: You are on the CC list for the bug.
