@@ -15,9 +15,9 @@
#define BTI_J hint 36 ;
/*
- * When using in-kernel BTI we need to ensure that assembly functions
- * have suitable annotations. Override SYM_FUNC_START to insert a BTI
- * landing pad at the start of everything.
+ * When using in-kernel BTI we need to ensure that PCS-conformant assembly
+ * functions have suitable annotations. Override SYM_FUNC_START to insert
+ * a BTI landing pad at the start of everything.
*/
#define SYM_FUNC_START(name) \
SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
@@ -15,7 +15,14 @@
.text
nop
-SYM_FUNC_START(__kernel_rt_sigreturn)
+/*
+ * GDB relies on being able to identify the sigreturn instruction sequence to
+ * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START()
+ * here, as it will emit a BTI C instruction and break the unwinder. Thankfully,
+ * this function is only ever called from a RET and so omitting the landing pad
+ * is perfectly fine.
+ */
+SYM_CODE_START(__kernel_rt_sigreturn)
.cfi_startproc
.cfi_signal_frame
.cfi_def_cfa x29, 0
@@ -24,6 +31,6 @@ SYM_FUNC_START(__kernel_rt_sigreturn)
mov x8, #__NR_rt_sigreturn
svc #0
.cfi_endproc
-SYM_FUNC_END(__kernel_rt_sigreturn)
+SYM_CODE_END(__kernel_rt_sigreturn)
emit_aarch64_feature_1_and
@@ -17,39 +17,39 @@
.save {r0-r15}
.pad #COMPAT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_sigreturn_arm)
+SYM_CODE_START(__kernel_sigreturn_arm)
mov r7, #__NR_compat_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_sigreturn_arm)
+SYM_CODE_END(__kernel_sigreturn_arm)
.fnstart
.save {r0-r15}
.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_rt_sigreturn_arm)
+SYM_CODE_START(__kernel_rt_sigreturn_arm)
mov r7, #__NR_compat_rt_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_rt_sigreturn_arm)
+SYM_CODE_END(__kernel_rt_sigreturn_arm)
.thumb
.fnstart
.save {r0-r15}
.pad #COMPAT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_sigreturn_thumb)
+SYM_CODE_START(__kernel_sigreturn_thumb)
mov r7, #__NR_compat_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_sigreturn_thumb)
+SYM_CODE_END(__kernel_sigreturn_thumb)
.fnstart
.save {r0-r15}
.pad #COMPAT_RT_SIGFRAME_REGS_OFFSET
nop
-SYM_FUNC_START(__kernel_rt_sigreturn_thumb)
+SYM_CODE_START(__kernel_rt_sigreturn_thumb)
mov r7, #__NR_compat_rt_sigreturn
svc #0
.fnend
-SYM_FUNC_END(__kernel_rt_sigreturn_thumb)
+SYM_CODE_END(__kernel_rt_sigreturn_thumb)
For better or worse, GDB relies on the exact instruction sequence in the VDSO sigreturn trampoline in order to unwind from signals correctly. Commit c91db232da48 ("arm64: vdso: Convert to modern assembler annotations") unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn, which breaks this check. Thankfully, it's also not required, since the trampoline is called from a RET instruction when returning from the signal handler Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn, and do the same for the 32-bit VDSO as well for good measure. Cc: Daniel Kiss <daniel.kiss@arm.com> Cc: Tamas Zsoldos <tamas.zsoldos@arm.com> Reviewed-by: Dave Martin <dave.martin@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Fixes: c91db232da48 ("arm64: vdso: Convert to modern assembler annotations") Signed-off-by: Will Deacon <will@kernel.org> --- arch/arm64/include/asm/linkage.h | 6 +++--- arch/arm64/kernel/vdso/sigreturn.S | 11 +++++++++-- arch/arm64/kernel/vdso32/sigreturn.S | 16 ++++++++-------- 3 files changed, 20 insertions(+), 13 deletions(-)