[gcc r11-1963] aarch64: Fix BTI support in libgcc [PR96001]

[Szabolcs Nagy]

https://gcc.gnu.org/g:f0f62fa0320762119446893c67cb52934bc5a05e

commit r11-1963-gf0f62fa0320762119446893c67cb52934bc5a05e
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Jul 2 17:11:56 2020 +0100

    aarch64: Fix BTI support in libgcc [PR96001]
    
    lse.S did not have the GNU property note markup and the BTI c
    instructions that are necessary when it is built with branch
    protection.
    
    The notes are only added when libgcc is built with branch
    protection, because old linkers mishandle the note (merge
    them incorrectly or emit warnings), the BTI instructions
    are added unconditionally.
    
    Note: BTI c is only necessary at function entry if the function
    may be called indirectly, currently lse functions are not called
    indirectly, but BTI is added for ABI reasons e.g. to allow
    linkers later to emit stub code with indirect jump.
    
    2020-07-09  Szabolcs Nagy  <szabolcs.nagy@arm.com>
    
    libgcc/ChangeLog:
    
            PR target/96001
            * config/aarch64/lse.S: Add BTI marking and related definitions,
            and add BTI c to function entries.

Diff:
---
 libgcc/config/aarch64/lse.S | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/libgcc/config/aarch64/lse.S b/libgcc/config/aarch64/lse.S
index 9e2acae806b..64691c601c1 100644
--- a/libgcc/config/aarch64/lse.S
+++ b/libgcc/config/aarch64/lse.S
@@ -136,6 +136,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define tmp1	17
 #define tmp2	15
 
+#define BTI_C	hint	34
+
 /* Start and end a function.  */
 .macro	STARTFN name
 	.text
@@ -145,6 +147,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 	.type	\name, %function
 	.cfi_startproc
 \name:
+	BTI_C
 .endm
 
 .macro	ENDFN name
@@ -275,6 +278,29 @@ STARTFN	NAME(LDNM)
 ENDFN	NAME(LDNM)
 #endif
 
+/* GNU_PROPERTY_AARCH64_* macros from elf.h for use in asm code.  */
+#define FEATURE_1_AND 0xc0000000
+#define FEATURE_1_BTI 1
+#define FEATURE_1_PAC 2
+
+/* Add a NT_GNU_PROPERTY_TYPE_0 note.  */
+#define GNU_PROPERTY(type, value)	\
+  .section .note.gnu.property, "a";	\
+  .p2align 3;				\
+  .word 4;				\
+  .word 16;				\
+  .word 5;				\
+  .asciz "GNU";				\
+  .word type;				\
+  .word 4;				\
+  .word value;				\
+  .word 0;
+
 #if defined(__linux__) || defined(__FreeBSD__)
 .section .note.GNU-stack, "", %progbits
+
+/* Add GNU property note if built with branch protection.  */
+# ifdef __ARM_FEATURE_BTI_DEFAULT
+GNU_PROPERTY (FEATURE_1_AND, FEATURE_1_BTI)
+# endif
 #endif