" On Wed, Nov 13, 2024 at 7:55 AM Maciej W. Rozycki <macro@xxxxxxxxxxx> wrote: > > On Tue, 12 Nov 2024, Rong Xu wrote: > > > The _stext symbol is intended to reference the start of the text section. > > However, it currently relies on a fragile link order because the existing > > EXPORT(_stext) resides within the .text section, which is not guaranteed > > to be placed first. > > Umm, arch/mips/kernel/head.S does mean to be linked first. We rely on it > for environments where there's no entry point is available and execution > starts from the beginning of the image. See the comment right below your > change. > When you said "arch/mips/kernel/head.S does mean to be linked first", is it a hard requirement in mips? This patch only moves _stext but leaves other symbols from heads.S for TEXT_TEXT macro to order. For example, __kernel_entry is placed in the middle of the text segment. If we want head.S to be linked first, I can change the patch to place all symbols from head.S before TEXT_TEXT. This way, we can also resolve your concerns about moving _stext byond the exception handlers. I tried that method, and the symbol order is like the following: 0100000 T _text 80100400 T __kernel_entry 80100400 T _stext 80100410 T file_ra_state_init 80100450 T readahead_expand 80100710 t read_pages 80100a04 T page_cache_ra_unbounded 80100c10 t do_page_cache_ra 80100c9c T force_page_cache_ra 80100d50 T page_cache_ra_order 80100d8c T page_cache_sync_ra 80100ff4 T page_cache_async_ra 801011b8 T ksys_readahead 801012cc T __se_sys_readahead 801012cc T sys_readahead 801012e0 T __split_text_end 801012e0 T __split_text_start 801012e0 t __sync ... Note that the reserve space for exceptions is before _stext > > Move the _stext definition to the linker script to enforce an explicit > > ordering. > > So if you say that the link order is fragile (which it may well be), then > that problem has to be fixed instead, likely with the linker script too, I think what we meant was the way the current vmlinux.lds.S (linker script) written makes the symbol ordering fragile. This patch is to fix this. > and then perhaps an ASSERT placed there to verify that it has worked and > `_stext' refers to the beginning, taking into account what follows too. > > Also note that `_stext' currently points beyond the space reserved for > exception handlers. Have you analysed what the consequences would be if > it was moved ahead of it, which your change does AFAICT? I did not analyze this. I think it's fine. From section boundaries guideline in include/asm-generic/sections.h It seems ok to me that exception handlers are included in [_stext, _etext]. But I admit that I'm not an expert here. We can use the method I mentioned above to keep current behavior. > Maciej
