[Buildroot] USE_BX=n on armv4 generate bx instruction

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear |~?~| demoniark |~?~|,

On Fri, 14 Feb 2014 00:02:18 +0100, |~?~| demoniark |~?~| wrote:
> I'm tring to self compile a system for my ib-nas-4220-b which embed a fa526
> cpu.
> I'm using buildroot v2013.11 with compiling kernel 3.12.
> My configs files are here:
> buildroot config:
> https://paste.ydct.org/?d7d79d21da6e34dc#cIrSeqbdDpbAvA3d55DoH36Eb417bDysMEjmtaYaaZU=
> busybox config:
> https://paste.ydct.org/?a1a61121ae4be30f#cBDY3H89/m4owEwtCO0Mv6nI0WFhScBuwJ92V/zyOPE=
> kernel config:
> https://paste.ydct.org/?a3035f3c2a153083#w7dWY4LuBgoSMXDWn7alrIuueR1x+Gc75Rt6nlZLS2I=
> uclibc config:
> https://paste.ydct.org/?91bbe608fe4be481#JRt/Zd/1I5VOmyYldmUK+2L1fxM0sSHDbplmZxGXPxM=
> When I try to boot my kernel with internet found filesystem, the nas boots.
> When the nas boot with the filesystem compiled with buildroot I get:
> [    4.630000] init (1): undefined instruction: pc=b6f0df40
> [    4.640000] Code: e5803180 e5802188 e580c18c e8bd4038 (e12fff1e)
> [    4.650000] Kernel panic - not syncing: Attempted to kill init!
> exitcode=0x00000004
> [    4.650000]
> [    4.650000] CPU: 0 PID: 1 Comm: init Not tainted 3.12.1 #2
> [    4.650000] Backtrace:
> [    4.650000] [<c001119c>] (dump_backtrace+0x0/0x10c) from [<c001153c>]
> (show_stack+0x18/0x1c)
> [    4.650000]  r6:c7825be0 r5:c0c78de0 r4:c072c728 r3:00000204
> [    4.650000] [<c0011524>] (show_stack+0x0/0x1c) from [<c05a3880>]
> (dump_stack+0x20/0x28)
> [    4.650000] [<c05a3860>] (dump_stack+0x0/0x28) from [<c059f8e0>]
> (panic+0x80/0x1d4)
> [    4.650000] [<c059f860>] (panic+0x0/0x1d4) from [<c001bf94>]
> (do_exit+0x388/0x75c)
> [    4.650000]  r3:c7829c40 r2:c7825cd0 r1:00000004 r0:c065552f
> [    4.650000]  r7:c0c78e10
> [    4.650000] [<c001bc0c>] (do_exit+0x0/0x75c) from [<c001c428>]
> (do_group_exit+0x88/0xc4)
> [    4.650000]  r7:c7829c40
> [    4.650000] [<c001c3a0>] (do_group_exit+0x0/0xc4) from [<c0026018>]
> (get_signal_to_deliver+0x40c/0x458)
> [    4.650000]  r4:c7826000 r3:80000013
> [    4.650000] [<c0025c0c>] (get_signal_to_deliver+0x0/0x458) from
> [<c059f3c4>] (do_signal+0xa0/0x3c0)
> [    4.650000] [<c059f324>] (do_signal+0x0/0x3c0) from [<c0010f28>]
> (do_work_pending+0x64/0xbc)
> [    4.650000] [<c0010ec4>] (do_work_pending+0x0/0xbc) from [<c000e9dc>]
> (work_pending+0xc/0x20)
> [    4.650000]  r6:ffffffff r5:60000010 r4:b6f0df40 r3:c7825be0
> With objdump fautly code e12fff1e appears to be the assembly 'bx'
> instruction. However, due to arm.com (
> http://infocenter.arm.com/help/topic/com.arm.doc.dui0204j/Cihfddaf.html#Cihiiajh
> ),
> I suppose that this instruction is not implemented in my farraday 526
> processor (an old armv4).
> In reference of this patch:
> http://git.buildroot.net/buildroot/commit/?id=9474421da36d8602f56b84b150e4cf4c78e788b3
> [*
> Fix uClibc USE_BX logic, it was always on, this would break the new
> FA526/626 support and broke StrongARM since it's a v4 core.] I understood
> it was corrected.
> So my question is next: what i'm doing wrong/missing?

Thanks a lot for your very detailed report, great to see people
reporting precise bugs, with all the details (configuration files,
Buildroot version, things that are happening, and the beginning of an
analysis).

Would you mind retrying with 2014.02-rc1, which has been recently
released? It might be possible that the commit
http://git.buildroot.net/buildroot/commit/arch/Config.in.arm?id=d3539dd53bf9e37538fd4d8b89783a11fded119f,
which has been merged after 2013.11, is fixing the problem you're
reporting.

If not, then please get back to us again, and I'll have a look.

Thanks again for your report!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com