linux-kernel - [PATCH 3.12 59/76] ARM: OMAP3: Fix booting with thumb2 kernel

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Date:	Thu, 19 May 2016 11:08:21 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 59/76] ARM: OMAP3: Fix booting with thumb2 kernel

From: Tony Lindgren <tony@...mide.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit d8a50941c91a68da202aaa96a3dacd471ea9c693 upstream.

We get a NULL pointer dereference on omap3 for thumb2 compiled kernels:

Internal error: Oops: 80000005 [#1] SMP THUMB2
...
[<c046497b>] (_raw_spin_unlock_irqrestore) from [<c0024375>]
(omap3_enter_idle_bm+0xc5/0x178)
[<c0024375>] (omap3_enter_idle_bm) from [<c0374e63>]
(cpuidle_enter_state+0x77/0x27c)
[<c0374e63>] (cpuidle_enter_state) from [<c00627f1>]
(cpu_startup_entry+0x155/0x23c)
[<c00627f1>] (cpu_startup_entry) from [<c06b9a47>]
(start_kernel+0x32f/0x338)
[<c06b9a47>] (start_kernel) from [<8000807f>] (0x8000807f)

The power management related assembly on omaps needs to interact with
ARM mode bootrom code, so we need to keep most of the related assembly
in ARM mode.

Turns out this error is because of missing ENDPROC for assembly code
as suggested by Stephen Boyd <sboyd@...eaurora.org>. Let's fix the
problem by adding ENDPROC in two places to sleep34xx.S.

Let's also remove the now duplicate custom code for mode switching.
This has been unnecessary since commit 6ebbf2ce437b ("ARM: convert
all "mov.* pc, reg" to "bx reg" for ARMv6+").

And let's also remove the comments about local variables, they are
now just confusing after the ENDPROC.

The reason why ENDPROC makes a difference is it sets .type and then
the compiler knows what to do with the thumb bit as explained at:

https://wiki.ubuntu.com/ARM/Thumb2PortingHowto

Reported-by: Kevin Hilman <khilman@...nel.org>
Tested-by: Kevin Hilman <khilman@...aro.org>
Signed-off-by: Tony Lindgren <tony@...mide.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/arm/mach-omap2/sleep34xx.S | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/arch/arm/mach-omap2/sleep34xx.S b/arch/arm/mach-omap2/sleep34xx.S
index d1dedc8195ed..eafd120b53f1 100644
--- a/arch/arm/mach-omap2/sleep34xx.S
+++ b/arch/arm/mach-omap2/sleep34xx.S
@@ -203,23 +203,8 @@ save_context_wfi:
 	 */
 	ldr	r1, kernel_flush
 	blx	r1
-	/*
-	 * The kernel doesn't interwork: v7_flush_dcache_all in particluar will
-	 * always return in Thumb state when CONFIG_THUMB2_KERNEL is enabled.
-	 * This sequence switches back to ARM.  Note that .align may insert a
-	 * nop: bx pc needs to be word-aligned in order to work.
-	 */
- THUMB(	.thumb		)
- THUMB(	.align		)
- THUMB(	bx	pc	)
- THUMB(	nop		)
-	.arm
-
 	b	omap3_do_wfi
-
-/*
- * Local variables
- */
+ENDPROC(omap34xx_cpu_suspend)
 omap3_do_wfi_sram_addr:
 	.word omap3_do_wfi_sram
 kernel_flush:
@@ -364,10 +349,7 @@ exit_nonoff_modes:
  * ===================================
  */
 	ldmfd	sp!, {r4 - r11, pc}	@ restore regs and return
-
-/*
- * Local variables
- */
+ENDPROC(omap3_do_wfi)
 sdrc_power:
 	.word	SDRC_POWER_V
 cm_idlest1_core:
-- 
2.8.2