On Sat, Jul 10, 2021 at 6:13 PM Bin Meng [off-list ref] wrote:

Hi Anup,

On Sat, Jul 10, 2021 at 6:42 PM Anup Patel [off-list ref] wrote:

quoted

Hi Bin,

On Sat, Jul 10, 2021 at 2:23 PM Bin Meng [off-list ref] wrote:

quoted

On Sat, Jul 10, 2021 at 10:56 AM Bin Meng [off-list ref] wrote:

quoted

On Sat, Jul 10, 2021 at 3:35 AM Jessica Clarke [off-list ref] wrote:

quoted

When using Clang with a bare-metal triple, -pie does not get passed to
the linker as it's not normally a thing that makes sense. However, in
our case it is, and manually forwarding it on works as desired, so do so
to fully support FW_PIC with Clang, including when linking with LLD.
---
 firmware/objects.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/firmware/objects.mk b/firmware/objects.mk
index ce91c2f..3bc83cd 100644
--- a/firmware/objects.mk
+++ b/firmware/objects.mk

@@ -21,7 +21,7 @@ ifeq ($(FW_PIC),y)
 firmware-genflags-y += -DFW_PIC
 firmware-asflags-y  += -fpic
 firmware-cflags-y   += -fPIE -pie
-firmware-ldflags-y  +=  -Wl,--no-dynamic-linker
+firmware-ldflags-y  +=  -Wl,--no-dynamic-linker -Wl,-pie
 endif

Does this manual forwarding also work for GNU ld? If so, I think we
don't need to detect bare-metal triple and turn off FW_PIC in
Makefile?

I just built a riscv64-unknown-elf-gcc toolchain and used it to build
the current HEAD of opensbi/master. Indeed it's broken that pie is not
supported with the bare-metal triple.

The GNU ld simply complains:

 ELF       platform/generic/firmware/payloads/test.elf
/opt/riscv-unknown-elf/lib/gcc/riscv64-unknown-elf/10.1.0/../../../../riscv64-unknown-elf/bin/ld.bfd:
-pie not supported

The firmware/objects.mk is doing the following:

ifndef FW_PIC
FW_PIC := y
endif

Instead of above, we should set FW_PIC=y only when the underlying
toolchain supports pie.

Agree.

quoted

We need a patch for this to be merged before we can merge this
series. Can you send such a patch ? If not then I can send it.

Do you have some reliable ways to check whether a toolchain supports PIE?

How about checking "-linux-" in CROSS_COMPILE prefix ? If it's available then
we set FW_PIC=y else we set FW_PIC=n. I did not find any info in the
"${CROSS_COMPILE}gcc -v" output.

Maybe also add some comment in objects.mk that GCC bare-metal toolchain
does not have PIE enabled.

Regards,
Anup

Regards,
Bin