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authorFlorian Fainelli <florian@openwrt.org>2013-03-18 15:56:10 +0000
committerRalf Baechle <ralf@linux-mips.org>2013-03-19 19:15:35 +0100
commit63c2b6812f1dc0beda4d6adad0365e048aa693e2 (patch)
treebfcb619a1130e1b2a6153d45fa46f61af8e08e53 /arch/mips/kernel/Makefile
parenta4285b99e0087361c61f51c819633382fa659ea6 (diff)
downloadvexpress-lsk-63c2b6812f1dc0beda4d6adad0365e048aa693e2.tar.gz
MIPS: Fix code generation for non-DSP capable CPUs
Commit 32a7ede (MIPS: dsp: Add assembler support for DSP ASEs) has enabled the use of DSP ASE specific instructions such as rddsp and wrdsp under the idea that all code path that will make use of these two instructions are properly checking for cpu_has_dsp to ensure that the particular CPU we are running on *actually* supports DSP ASE. This commit actually causes the following oops on QEMU Malta emulating a MIPS 24Kc without the DSP ASE implemented: [ 7.960000] Reserved instruction in kernel [ 7.960000] Cpu 0 [ 7.960000] $ 0 : 00000000 00000000 00000014 00000005 [ 7.960000] $ 4 : 8fc2de48 00000001 00000000 8f59ddb0 [ 7.960000] $ 8 : 8f5ceec4 00000018 00000c00 00800000 [ 7.960000] $12 : 00000100 00000200 00000000 00457b84 [ 7.960000] $16 : 00000000 8fc2ba78 8f4ec980 00000001 [ 7.960000] $20 : 80418f90 00000000 00000000 000002dd [ 7.960000] $24 : 0000009c 7730d7b8 [ 7.960000] $28 : 8f59c000 8f59dd38 00000001 80104248 [ 7.960000] Hi : 0000001d [ 7.960000] Lo : 0000000b [ 7.960000] epc : 801041ec thread_saved_pc+0x2c/0x38 [ 7.960000] Not tainted [ 7.960000] ra : 80104248 get_wchan+0x48/0xac [ 7.960000] Status: 1000b703 KERNEL EXL IE [ 7.960000] Cause : 10800028 [ 7.960000] PrId : 00019300 (MIPS 24Kc) [ 7.960000] Modules linked in: [ 7.960000] Process killall (pid: 1574, threadinfo=8f59c000, task=8fd14558, tls=773aa440) [ 7.960000] Stack : 8fc2ba78 8012b008 0000000c 0000001d 00000000 00000000 8f58a380 8f58a380 8fc2ba78 80202668 8f59de78 8f468600 8f59de28 801b2a3c 8f59df00 8f98ba20 74696e69 8f468600 8f59de28 801b7308 0081c007 00000000 00000000 00000000 00000000 00000000 00000000 00000000 8fc2bbb4 00000001 0000001d 0000000b 77f038cc 7fe80648 ffffffff ffffffff 00000000 00000001 0016e000 00000000 ... [ 7.960000] Call Trace: [ 7.960000] [<801041ec>] thread_saved_pc+0x2c/0x38 [ 7.960000] [<80104248>] get_wchan+0x48/0xac The disassembly of thread_saved_pc points to the following: 000006d0 <thread_saved_pc>: 6d0: 8c820208 lw v0,520(a0) 6d4: 3c030000 lui v1,0x0 6d8: 24630000 addiu v1,v1,0 6dc: 10430008 beq v0,v1,700 <thread_saved_pc+0x30> 6e0: 00000000 nop 6e4: 3c020000 lui v0,0x0 6e8: 8c43000c lw v1,12(v0) 6ec: 04620004 bltzl v1,700 <thread_saved_pc+0x30> 6f0: 00001021 move v0,zero 6f4: 8c840200 lw a0,512(a0) 6f8: 00031080 sll v0,v1,0x2 6fc: 7c44100a lwx v0,a0(v0) <------------ 700: 03e00008 jr ra 704: 00000000 nop If we specifically disable -mdsp/-mdspr2 for arch/mips/kernel/process.o, we get the following (non-crashing) assembly: 00000708 <thread_saved_pc>: 708: 8c820208 lw v0,520(a0) 70c: 3c030000 lui v1,0x0 710: 24630000 addiu v1,v1,0 714: 10430009 beq v0,v1,73c <thread_saved_pc+0x34> 718: 00000000 nop 71c: 3c020000 lui v0,0x0 720: 8c42000c lw v0,12(v0) 724: 04420005 bltzl v0,73c <thread_saved_pc+0x34> 728: 00001021 move v0,zero 72c: 8c830200 lw v1,512(a0) 730: 00021080 sll v0,v0,0x2 734: 00431021 addu v0,v0,v1 738: 8c420000 lw v0,0(v0) 73c: 03e00008 jr ra 740: 00000000 nop The specific line that leads a different assembly being produced is: unsigned long thread_saved_pc(struct task_struct *tsk) ... return ((unsigned long *)t->reg29)[schedule_mfi.pc_offset]; <--- The problem here is that the compiler was given the right to use DSP instructions with the -mdsp / -mdspr2 command-line switches and performed some optimization for us and used DSP ASE instructions where we are not checking that the running CPU actually supports DSP ASE. This patch fixes the issue by partially reverting commit 32a7ede for arch/mips/kernel/Makefile in order to remove the -mdsp / -mdspr2 compiler command-line switches such that we are now guaranteed that the compiler will not optimize using DSP ASE reserved instructions. We also need to fixup the rddsp/wrdsp and m{t,h}{hi,lo}{0,1,2,3} macros in arch/mips/include/asm/mipsregs.h to tell the assembler that we are going to explicitely use DSP ASE reserved instructions. The comment in arch/mips/kernel/Makefile is also updated to reflect that. Signed-off-by: Florian Fainelli <florian@openwrt.org> Acked-by: Steven J. Hill <Steven.Hill@imgtec.com> Cc: linux-mips@linux-mips.org Cc: blogic@openwrt.org Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch/mips/kernel/Makefile')
-rw-r--r--arch/mips/kernel/Makefile25
1 files changed, 6 insertions, 19 deletions
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index f81d98f6184..de75fb50562 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -100,29 +100,16 @@ obj-$(CONFIG_HW_PERF_EVENTS) += perf_event_mipsxx.o
obj-$(CONFIG_JUMP_LABEL) += jump_label.o
#
-# DSP ASE supported for MIPS32 or MIPS64 Release 2 cores only. It is safe
-# to enable DSP assembler support here even if the MIPS Release 2 CPU we
-# are targetting does not support DSP because all code-paths making use of
-# it properly check that the running CPU *actually does* support these
-# instructions.
+# DSP ASE supported for MIPS32 or MIPS64 Release 2 cores only. It is not
+# safe to unconditionnaly use the assembler -mdsp / -mdspr2 switches
+# here because the compiler may use DSP ASE instructions (such as lwx) in
+# code paths where we cannot check that the CPU we are running on supports it.
+# Proper abstraction using HAVE_AS_DSP and macros is done in
+# arch/mips/include/asm/mipsregs.h.
#
ifeq ($(CONFIG_CPU_MIPSR2), y)
CFLAGS_DSP = -DHAVE_AS_DSP
-#
-# Check if assembler supports DSP ASE
-#
-ifeq ($(call cc-option-yn,-mdsp), y)
-CFLAGS_DSP += -mdsp
-endif
-
-#
-# Check if assembler supports DSP ASE Rev2
-#
-ifeq ($(call cc-option-yn,-mdspr2), y)
-CFLAGS_DSP += -mdspr2
-endif
-
CFLAGS_signal.o = $(CFLAGS_DSP)
CFLAGS_signal32.o = $(CFLAGS_DSP)
CFLAGS_process.o = $(CFLAGS_DSP)