? 2021-07-10???? 20:26 +0530?Anup Patel???

On Sat, Jul 10, 2021 at 7:13 PM Bin Meng [off-list ref] wrote:

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On Sat, Jul 10, 2021 at 9:38 PM Anup Patel [off-list ref]
wrote:

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

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Hi Anup,

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

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Hi Bin,

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

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On Sat, Jul 10, 2021 at 10:56 AM Bin Meng <
bmeng.cn at gmail.com> wrote:

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On Sat, Jul 10, 2021 at 3:35 AM Jessica Clarke <
jrtc27 at jrtc27.com> wrote:

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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.

That works for cross-compile toolchains. But how about native
toolchains (building OpenSBI on a RISC-V machine)?

Yes, it will not work for native compilation of OpenSBI.

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I did not find any info in the "${CROSS_COMPILE}gcc -v" output.

Me neither.

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

Or we can just document if using bare-metal toolchain FW_PIC has to
be
set to n in the build.

Sounds good.

We should document it under section "Required Toolchain" of top-level
README.md. Basically, we prefer toolchains with PIE support and for
toolchains not having PIE users have to pass the "FW_PIC=n" option.

Also, we should replace references of bare-metal toolchain prefix
with
linux toolchain prefix everywhere in documentation.

Regards,
Anup

We can add the following code to the makefile to detect pie support

pie_support=$(shell $(CC) -nostdlib -fPIE -Wl,-pie /dev/null
2>/dev/null && echo y || echo n)

quoted

Regards,
Bin