On Fri, May 12, 2023 at 02:25:28AM +0000, Fangrui Song wrote: > Tools like readelf/llvm-readelf use p_align to parse a PT_NOTE program > header as an array of 4-byte entries or 8-byte entries. Currently, there > are workarounds[1] in place for Linux to treat p_align==0 as 4. However, > it would be more appropriate to set the correct alignment so that tools > do not have to rely on guesswork. FreeBSD coredumps set p_align to 4 as > well. > > [1]: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=82ed9683ec099d8205dc499ac84febc975235af6 The interesting bit from here is: /* NB: Some note sections may have alignment value of 0 or 1. gABI specifies that notes should be aligned to 4 bytes in 32-bit objects and to 8 bytes in 64-bit objects. As a Linux extension, we also support 4 byte alignment in 64-bit objects. If section alignment is less than 4, we treate alignment as 4 bytes. */ if (align < 4) align = 4; else if (align != 4 && align != 8) { warn (_("Corrupt note: alignment %ld, expecting 4 or 8\n"), (long) align); return FALSE; } Should Linux use 8 for 64-bit processes to avoid the other special case? (And do we need to make some changes to make sure we are actually aligned?) -Kees -- Kees Cook
