commit 559f27828cbc51851978c5781618fe5b3d34e4ba
author Chris Wailes <chriswailes@google.com> Mon May 03 14:27:12 2021 -0700
committer Chris Wailes <chriswailes@google.com> Fri May 07 15:00:55 2021 -0700
tree 4b6cb79ec78207cbe3faa1fab72597db1c436b07
parent 3e0defac5d546c3a0ed0f5faae1a40502ffac003

Clear the stack frame pointer in _start and __bionic_clone

This CL adds an instruction to the _start label that clears the frame
pointer.  This allows stack walking code to determine when it has
reached the end of the stack.

The __bionic_clone function is similarly modified, for architectures
that weren't already doing both.

Test: bionic-unit-tests
Test: CtsBionicTestCases
Change-Id: Iea3949f52c44f7931f9fff2d60d4d9e5c742c120

libc/arch-arm/bionic/__bionic_clone.S

diff --git a/libc/arch-arm/bionic/__bionic_clone.S b/libc/arch-arm/bionic/__bionic_clone.S
index 6669b93..3fe212b 100644
--- a/libc/arch-arm/bionic/__bionic_clone.S
+++ b/libc/arch-arm/bionic/__bionic_clone.S
@@ -61,6 +61,8 @@
     b       __set_errno_internal
 
 .L_bc_child:
+    # We're in the child now. Set the end of the frame record chain.
+    mov    fp, #0
     # Setting lr to 0 will make the unwinder stop at __start_thread.
     mov    lr, #0
     # Call __start_thread with the 'fn' and 'arg' we stored on the child stack.