fix(cpufeat): replace "bti" mnemonic with hint instructions
Older GNU binutils version require to specify at least "armv8.5-a" for
the ARM architecture revision to accept "bti" instructions in the
assembly code. Binutils v2.35 have relaxed this, since "bti" is in the
hint space, so is ignored on older cores and does NOT require a BTI
enabled core to execute.
To not exclude those older binutils versions (as shipped with Ubuntu
20.04), use the "hint" encoding for the "bti" instructions, which are
accepted regardless of the minimum architecture revision. Hide this
encoding in a macro, to make the "bti" usage more readable in the
source code.
Change-Id: I005586efd8974a3f2c7202896c881bb5fed07eea
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/include/arch/aarch64/asm_macros.S b/include/arch/aarch64/asm_macros.S
index da51bf8..0afc9c2 100644
--- a/include/arch/aarch64/asm_macros.S
+++ b/include/arch/aarch64/asm_macros.S
@@ -230,7 +230,7 @@
*/
.macro read reg:req
#if ENABLE_BTI
- bti j
+ BTI j
#endif
mrs x0, \reg
ret
@@ -241,7 +241,7 @@
*/
.macro write reg:req
#if ENABLE_BTI
- bti j
+ BTI j
#endif
msr \reg, x1
ret
diff --git a/include/common/asm_macros_common.S b/include/common/asm_macros_common.S
index fd0ea81..9172b55 100644
--- a/include/common/asm_macros_common.S
+++ b/include/common/asm_macros_common.S
@@ -7,6 +7,20 @@
#define ASM_MACROS_COMMON_S
/*
+ * Provide a wrapper for the "bti" instructions using the more
+ * compatible "hint" encoding, otherwise older toolchains would reject
+ * this when not compiled for a BTI capable machine (-march=armv8.5-a).
+ */
+ .macro BTI _targets
+ .ifc \_targets, j
+ hint #36
+ .endif
+ .ifc \_targets, jc
+ hint #38
+ .endif
+ .endm
+
+ /*
* This macro is used to create a function label and place the
* code into a separate text section based on the function name
* to enable elimination of unused code during linking. It also adds
@@ -42,7 +56,7 @@
/* When Branch Target Identification is enabled, insert "bti jc"
* instruction to enable indirect calls and branches
*/
- bti jc
+ BTI jc
#endif
.endm
diff --git a/include/lib/cpus/aarch64/cpu_macros.S b/include/lib/cpus/aarch64/cpu_macros.S
index c43beb6..d303a70 100644
--- a/include/lib/cpus/aarch64/cpu_macros.S
+++ b/include/lib/cpus/aarch64/cpu_macros.S
@@ -550,7 +550,7 @@
.align \_align
\_name:
#if ENABLE_BTI
- bti jc
+ BTI jc
#endif
.endm
diff --git a/lib/aarch64/cache_helpers.S b/lib/aarch64/cache_helpers.S
index ff9a4e6..cc46c53 100644
--- a/lib/aarch64/cache_helpers.S
+++ b/lib/aarch64/cache_helpers.S
@@ -215,7 +215,7 @@
.macro dcsw_loop _op
#if ENABLE_BTI
- bti j
+ BTI j
#endif
loop2_\_op:
lsl w7, w6, w2 // w7 = aligned max set number