[FFmpeg-devel] [PATCH v2] Add assembly support for -fsanitize=hwaddress tagged globals.

[Peter Collingbourne]

As of LLVM r368102, Clang will set a pointer tag in bits 56-63 of the
address of a global when compiling with -fsanitize=hwaddress. This requires
an adjustment to assembly code that takes the address of such globals: the
code cannot use the regular R_AARCH64_ADR_PREL_PG_HI21 relocation to refer
to the global, since the tag would take the address out of range. Instead,
the code must use the non-checking (_NC) variant of the relocation (the
link-time check is substituted by a runtime check).

This change makes the necessary adjustment in the movrel macro, where it is
needed when compiling with -fsanitize=hwaddress.

Signed-off-by: Peter Collingbourne <pcc at google.com>
---
 libavutil/aarch64/asm.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libavutil/aarch64/asm.S b/libavutil/aarch64/asm.S
index 5c329430fd..3ac2ba0d52 100644
--- a/libavutil/aarch64/asm.S
+++ b/libavutil/aarch64/asm.S
@@ -32,6 +32,10 @@
 #   define FUNC #
 #endif
 
+#ifndef __has_feature
+#   define __has_feature(x) 0
+#endif
+
 .macro  function name, export=0, align=2
     .macro endfunc
 ELF     .size   \name, . - \name
@@ -94,7 +98,11 @@ ELF     .size   \name, . - \name
         add             \rd, \rd, :lo12:\val+(\offset)
     .endif
 #elif CONFIG_PIC
+#   if __has_feature(hwaddress_sanitizer)
+        adrp            \rd, :pg_hi21_nc:\val+(\offset)
+#   else
         adrp            \rd, \val+(\offset)
+#   endif
         add             \rd, \rd, :lo12:\val+(\offset)
 #else
         ldr             \rd, =\val+\offset
-- 
2.23.0.187.g17f5b7556c-goog