On 21/07/2022 10:17, Andrea Corallo via Gcc-patches wrote:
Richard Earnshaw <richard.earns...@foss.arm.com> writes:
On 28/04/2022 10:48, Andrea Corallo via Gcc-patches wrote:
This change add bti instructions at the beginning of arm specific
libgcc hand written assembly routines.
2022-03-31 Andrea Corallo <andrea.cora...@arm.com>
* libgcc/config/arm/crti.S (FUNC_START): Add bti instruction
if
necessary.
* libgcc/config/arm/lib1funcs.S (THUMB_FUNC_START, FUNC_START):
Likewise.
+#if defined(__ARM_FEATURE_BTI)
Wouldn't it be better to use __ARM_FEATURE_BTI_DEFAULT? That way we
only get BTI instructions in multilib variants that have asked for
BTI.
R.
Hi Richard,
good point, yes I think so.
Please find attached the updated patch.
BR
Andrea
I've been pondering this patch. The way it is implemented would put a
BTI instruction at the start of every assembler routine in libgcc. But
the vast majority of functions in libgcc cannot have their address
taken, so a BTI isn't needed (BTI is only needed when an indirect jump
could be used). So I wonder if we really need to do this so aggressively?
Perhaps a better approach would be to define a macro (eg MAYBEBTI) which
expands a BTI if the compilation requires it and nothing otherwise), and
then manually insert that in any functions that really need this (if any).
R.
