Add arm32 case to BIONIC_STOP_UNWIND to correctly stop unwinders
The arm32 case was omitted when the macro was originally added due to
clang issues (b/15469122#comment5).
Testing at ToT master, ".cfi_undefined r14" appears to compile & work as
expected. This is the same directive as used by the linker's begin.S.
Test: ran a 32 bit binary on crosshatch-userdebug, verified that
"debuggerd -b" (which uses libunwindstack) stops at __libc_init as in
the arm64 case (before it would unwind past _start_main, with an
erroneous frame at the bottom).
Test: ran unwind_reg_info tool on /system/lib/libc.so with an address
within __libc_init, confirmed that the "debug_frame" section includes
"r14 = undefine" (arm exidx still contains "r14 = [cfa - 4]", but that
looked correct to cferris@).
Bug: 140008396
Change-Id: I6eb0bc6cf516fddee2df40492350678a0547fee3
diff --git a/libc/private/bionic_macros.h b/libc/private/bionic_macros.h
index 13934e5..54903f5 100644
--- a/libc/private/bionic_macros.h
+++ b/libc/private/bionic_macros.h
@@ -50,10 +50,7 @@
}
#if defined(__arm__)
-// Do not emit anything for arm, clang does not allow emiting an arm unwind
-// directive.
-// #define BIONIC_STOP_UNWIND asm volatile(".cantunwind")
-#define BIONIC_STOP_UNWIND
+#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined r14")
#elif defined(__aarch64__)
#define BIONIC_STOP_UNWIND asm volatile(".cfi_undefined x30")
#elif defined(__i386__)