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From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: barebox@lists.infradead.org
Subject: [BUG] Padding inserted by linker breaks magicvar linker array
Date: Mon, 4 Nov 2019 08:42:58 +0100	[thread overview]
Message-ID: <2c00f789-0630-5dca-d0a6-3aa33b03e1ce@pengutronix.de> (raw)

Hi,

I run into a crash with barebox master[1] when running the magicvar command.
The culprit seems to be 8 bytes of padding inserted between
__barebox_magicvar_start and OPTARG, the first array element:

                  0x0000000000061918                __barebox_magicvar_start = .
   *(SORT_BY_NAME(.barebox_magicvar*))
=> *fill*         0x0000000000061918        0x8
   .barebox_magicvar_OPTARG
                  0x0000000000061920       0x10 common/built-in.o
                  0x0000000000061920                __barebox_magicvar_OPTARG

The 8 byte *fill*er aligns the .barebox_magicvar_OPTARG section to 16 bytes.
Via addition and removal of dummy initcalls, we can shift the magicvars around
until we no longer straddle the 16 bit boundary:

                 0x0000000000061910                __barebox_magicvar_start = .
   *(SORT_BY_NAME(.barebox_magicvar*))
   .barebox_magicvar_OPTARG
                 0x0000000000061910       0x10 common/built-in.o
                 0x0000000000061910                __barebox_magicvar_OPTARG

Now running magicvar no longer crashes. We can achieve the alignment reliably by
adding . = ALIGN(16) at the start of the BAREBOX_MAGICVARS definition in
include/asm-generic/barebox.lds.h.

Does someone know what controls this 16 byte (or maybe 32 byte?) alignment?
Do we need to explicitly align the other linker array start symbols as well or
is there a better way?

Interestingly, the barebox_cmd array which I would've expected to behave the same
doesn't:

               0x0000000000061638                __barebox_cmd_start = .
*(SORT_BY_NAME(.barebox_cmd*))
.barebox_cmd_2048
               0x0000000000061638        0x8 commands/built-in.o
               0x0000000000061638                barebox_cmd_2048

Here the 8 byte alignment is deemed ok by the linker...

Thoughts?

Cheers,
Ahmad



[1]: master at time of writing is 27ee6010 "console_simple: fix linking error when
     ARCH_HAS_CTRLC enabled". To reproduce the issue I've added a single dummy initcall.
     I can provide defconfig if requested.
-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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             reply	other threads:[~2019-11-04  7:44 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04  7:42 Ahmad Fatoum [this message]
2019-11-04  8:36 ` Ahmad Fatoum

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