From 2b92982e2369d292560793bee8e730f695f48ff3 Mon Sep 17 00:00:00 2001 From: Michael Jeanson Date: Wed, 3 Jul 2024 12:35:34 -0400 Subject: nptl: fix potential merge of __rseq_* relro symbols While working on a patch to add support for the extensible rseq ABI, we came across an issue where a new 'const' variable would be merged with the existing '__rseq_size' variable. We tracked this to the use of '-fmerge-all-constants' which allows the compiler to merge identical constant variables. This means that all 'const' variables in a compile unit that are of the same size and are initialized to the same value can be merged. In this specific case, on 32 bit systems 'unsigned int' and 'ptrdiff_t' are both 4 bytes and initialized to 0 which should trigger the merge. However for reasons we haven't delved into when the attribute 'section (".data.rel.ro")' is added to the mix, only variables of the same exact types are merged. As far as we know this behavior is not specified anywhere and could change with a new compiler version, hence this patch. Move the definitions of these variables into an assembler file and add hidden writable aliases for internal use. This has the added bonus of removing the asm workaround to set the values on rseq registration. Tested on Debian 12 with GCC 12.2. Signed-off-by: Michael Jeanson Reviewed-by: Mathieu Desnoyers Reviewed-by: Florian Weimer --- elf/Makefile | 1 + 1 file changed, 1 insertion(+) (limited to 'elf/Makefile') diff --git a/elf/Makefile b/elf/Makefile index a3475f3..147f1d3 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -73,6 +73,7 @@ dl-routines = \ dl-origin \ dl-printf \ dl-reloc \ + dl-rseq-symbols \ dl-runtime \ dl-scope \ dl-setup_hash \ -- cgit v1.1