[PATCH v4 11/12] aarch64: redefine RETURN_ADDRESS to strip PAC
Fri Jun 12 13:29:29 GMT 2020
RETURN_ADDRESS is used at several places in glibc to mean a valid
code address of the call site, but with pac-ret it may contain a
pointer authentication code (PAC), so its definition is adjusted.
This is gcc PR target/95891: __builtin_return_address should not
expose signed pointers to user code where it can cause ABI issues.
In glibc RETURN_ADDRESS is only changed if it is built with pac-ret.
There is no detection for the specific gcc issue because it is
hard to test and the additional xpac does not cause problems.
sysdeps/aarch64/sysdep.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index 2879aeaa5c..593bdd35a2 100644
@@ -44,6 +44,13 @@ strip_pac (void *p)
asm ("hint 7 // xpaclri" : "+r"(ra));
+/* This is needed when glibc is built with -mbranch-protection=pac-ret
+ with a gcc that is affected by PR target/95891. */
+# if HAVE_AARCH64_PAC_RET
+# undef RETURN_ADDRESS
+# define RETURN_ADDRESS(n) strip_pac (__builtin_return_address (n))
More information about the Libc-alpha