[ARM] __cxa_end_cleanup: avoid clobbering r4 am: c0a6edcf3b am: 00928ed8ee
Original change: https://android-review.googlesource.com/c/platform/external/libcxxabi/+/2024827
Change-Id: I375e63b4b18f4832f19a591216b21118a4084ac7
diff --git a/src/cxa_exception.cpp b/src/cxa_exception.cpp
index 8d30e5c..9e650b5 100644
--- a/src/cxa_exception.cpp
+++ b/src/cxa_exception.cpp
@@ -343,8 +343,11 @@
According to ARM EHABI 8.4.1, __cxa_end_cleanup() should not clobber any
register, thus we have to write this function in assembly so that we can save
{r1, r2, r3}. We don't have to save r0 because it is the return value and the
-first argument to _Unwind_Resume(). In addition, we are saving r4 in order to
-align the stack to 16 bytes, even though it is a callee-save register.
+first argument to _Unwind_Resume(). The function also saves/restores r4 to
+keep the stack aligned and to provide a temp register. _Unwind_Resume never
+returns and we need to keep the original lr so just branch to it. When
+targeting bare metal, the function also clobbers ip/r12 to hold the address of
+_Unwind_Resume, which may be too far away for an ordinary branch.
*/
__attribute__((used)) static _Unwind_Exception *
__cxa_end_cleanup_impl()
@@ -374,20 +377,30 @@
return &exception_header->unwindHeader;
}
-asm (
- " .pushsection .text.__cxa_end_cleanup,\"ax\",%progbits\n"
+asm(" .pushsection .text.__cxa_end_cleanup,\"ax\",%progbits\n"
" .globl __cxa_end_cleanup\n"
" .type __cxa_end_cleanup,%function\n"
"__cxa_end_cleanup:\n"
+#if defined(__ARM_FEATURE_BTI_DEFAULT)
+ " bti\n"
+#endif
" push {r1, r2, r3, r4}\n"
+ " mov r4, lr\n"
" bl __cxa_end_cleanup_impl\n"
+ " mov lr, r4\n"
+#if defined(LIBCXXABI_BAREMETAL)
+ " ldr r4, =_Unwind_Resume\n"
+ " mov ip, r4\n"
+#endif
" pop {r1, r2, r3, r4}\n"
- " bl _Unwind_Resume\n"
- " bl abort\n"
- " .popsection"
-);
-#endif // defined(_LIBCXXABI_ARM_EHABI)
-
+#if defined(LIBCXXABI_BAREMETAL)
+ " bx ip\n"
+#else
+ " b _Unwind_Resume\n"
+#endif
+ " .popsection");
+#endif // defined(_LIBCXXABI_ARM_EHABI)
+
/*
This routine can catch foreign or native exceptions. If native, the exception
can be a primary or dependent variety. This routine may remain blissfully
