Hi,
On Tue, Dec 10, 2024 at 05:11:59PM +0100, Alexander Dahl wrote:
> I'm using nftables and on an armv5te target (microchip at91 sam9x60)
> the command `nft list ruleset` crashes with 'illegal instruction'.
>
> BSP is on ptxdist-2024.05.0 with the latest libgmp 6.3 backported from
> master. Toolchain is precompiled
> OSELAS.Toolchain-2023.07.1/arm-v5te-linux-gnueabi from
> debian.pengutronix.de, so overall nothing special.
>
> `ptxdist prepare libgmp` gives this (somewhere in between):
>
> using ABI="32"
> CC="arm-v5te-linux-gnueabi-gcc"
> CFLAGS="-O2 -pedantic -fomit-frame-pointer -march=armv4
> -mfloat-abi=softfp"
> CPPFLAGS=""
> MPN_PATH=" arm generic"
>
> After staring at configure.ac and configure I guess they try to be
> smart here, but do not detect the actual arch.
>
> Analzing the coredump with cgdb suggests it fails in __gmp_doprnt()
> shows this:
>
> 1│ Dump of assembler code for function __gmp_doprnt:
> 2│ 0xb6d69840 <+0>: push {r4, r5, r6, r7, r8, r9, r10, r11,
> lr}
> 3├──> 0xb6d69844 <+4>: vpush {d8}
> 4│ 0xb6d69848 <+8>: sub sp, sp, #132 @ 0x84
>
> That instruction seems to be some VFP related ARM floating point thing?
>
> I tried adding this to rules/libgmp.make:
>
> LIBGMP_CONF_ENV := \
> CFLAGS='-O2 -pedantic -g'
>
> This gives almost the same output of prepare, but with "my" cflags
> only, so without -march or -mfloat-abi and then nft does not crash
> anymore.
>
> I could use that as a workaround, but it seems to circumvent libgmp
> arch detection entirely, and so I'm not sure if that's the correct way
> here?
>
> btw, you can see libgmp autoconf is not so super smart, because this is the
> output of `ptxdist prepare libgmp` on v7a target:
>
> using ABI="32"
> CC="arm-v7a-linux-gnueabihf-gcc"
> CFLAGS="-O2 -pedantic -fomit-frame-pointer -march=armv4
> -mfloat-abi=hard"
> CPPFLAGS=""
> MPN_PATH=" arm generic"
>
> So it's still -march=armv4 here. But is that really necessary with
> the cross compiler at all?
Wow that detection is really confusing. And I'm not seeing anything there
that should be added to the CFLAGS. And somewhere in there I find: "Any
user CFLAGS, even an empty string, takes precedence".
So setting the CFLAGS works by design and I think it's the correct fix. But
please add a comment why this is necessary.
Michael
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