use explicit __cp_cancel label in cancellable syscall asm for all archs

previously, only archs that needed to do stack cleanup defined a
__cp_cancel label for acting on cancellation in their syscall asm, and
a default definition was provided by a weak alias to __cancel, the C
function. this resulted in wrong codegen for arm on gcc versions
affected by pr 68178 and possibly similar issues (like pr 66609) on
other archs, and also created an inconsistency where the __cp_begin
and __cp_end labels were treated as const data but __cp_cancel was
treated as a function. this in turn caused incorrect code generation
on archs where function pointers point to function descriptors rather
than code (for now, only sh/fdpic).

1 files changed, 3 insertions, 1 deletions

diff --git a/src/thread/x86_64/syscall_cp.s b/src/thread/x86_64/syscall_cp.s
index 1a0fd5d2..4f101716 100644
--- a/src/thread/x86_64/syscall_cp.s
+++ b/src/thread/x86_64/syscall_cp.s
@@ -14,7 +14,7 @@ __syscall_cp_asm:
 __cp_begin:
 	mov (%rdi),%eax
 	test %eax,%eax
-	jnz __cancel
+	jnz __cp_cancel
 	mov %rdi,%r11
 	mov %rsi,%rax
 	mov %rdx,%rdi
@@ -27,3 +27,5 @@ __cp_begin:
 	syscall
 __cp_end:
 	ret
+__cp_cancel:
+	jmp __cancel