From 91181954f94917b1e1ae591c60cbadf0321d35af Mon Sep 17 00:00:00 2001 From: Sudakshina Das Date: Tue, 17 Mar 2020 15:44:18 +0000 Subject: aarch64: Add BTI support to assembly files To enable building glibc with branch protection, assembly code needs BTI landing pads and ELF object file markings in the form of a GNU property note. The landing pads are unconditionally added to all functions that may be indirectly called. When the code segment is not mapped with PROT_BTI these instructions are nops. They are kept in the code when BTI is not supported so that the layout of performance critical code is unchanged across configurations. The GNU property notes are only added when there is support for BTI in the toolchain, because old binutils does not handle the notes right. (Does not know how to merge them nor to put them in PT_GNU_PROPERTY segment instead of PT_NOTE, and some versions of binutils emit warnings about the unknown GNU property. In such cases the produced libc binaries would not have valid ELF marking so BTI would not be enabled.) Note: functions using ENTRY or ENTRY_ALIGN now start with an additional BTI c, so alignment of the following code changes, but ENTRY_ALIGN_AND_PAD was fixed so there is no change to the existing code layout. Some string functions may need to be tuned for optimal performance after this commit. Co-authored-by: Szabolcs Nagy Reviewed-by: Adhemerval Zanella --- sysdeps/aarch64/start.S | 1 + 1 file changed, 1 insertion(+) (limited to 'sysdeps/aarch64/start.S') diff --git a/sysdeps/aarch64/start.S b/sysdeps/aarch64/start.S index d96cf57e2d..75393e1c18 100644 --- a/sysdeps/aarch64/start.S +++ b/sysdeps/aarch64/start.S @@ -46,6 +46,7 @@ .globl _start .type _start,#function _start: + BTI_C /* Create an initial frame with 0 LR and FP */ mov x29, #0 mov x30, #0 -- cgit 1.4.1