[RFC] ARM/mem: handle data aborts gracefully for md
Sascha Hauer
s.hauer at pengutronix.de
Thu Sep 4 23:44:45 PDT 2014
On Sun, Aug 03, 2014 at 05:51:38PM +0200, Jan Luebbe wrote:
> The current implementation breaks everything except ARM and takes several
> shortcuts which need to be implemented more cleanly. Suggestions are very
> welcome!
The following is much cleaner but still not ready. It still breaks
everything except ARM (and even ARM with exceptions disabled).
It also doesn't work properly. I had to make abort_conf volatile, but
even then with "md -b" the abort_conf value hasn't changed after an
abort. I had to read it again, then it changed its value. I think there
is some barrier missing.
------------------------8<---------------------------
>From 5793cd4beaccad0d3515296f2eb7b26f05613d04 Mon Sep 17 00:00:00 2001
From: Jan Luebbe <jlu at pengutronix.de>
Date: Sun, 3 Aug 2014 17:51:38 +0200
Subject: [PATCH] ARM/mem: handle data aborts gracefully for md
Sometimes memory ranges contain inaccessible registers which trigger a
data abort when accessed. To handle this gracefully, we extend the data
abort exception handler to ignore the exception when configured to do
so.
This allows detecting inaccessible memory from the md command. It will
show XX for unreadable bytes instead.
The previous behaviour:
barebox at TI AM335x BeagleBone:/ md 0x50000000
unable to handle paging request at address 0x500000ac
pc : [<8fe2e0dc>] lr : [<8fe2e0b9>]
sp : 8ffff898 ip : 00000024 fp : 00000000
r10: 8bfa0204 r9 : 00000000 r8 : 8bfa0204
r7 : 00000100 r6 : 50000000 r5 : 8bfa0204 r4 : 00000004
r3 : 00000f00 r2 : 000000ac r1 : 00000004 r0 : 00000014
Flags: nZCv IRQs off FIQs on Mode SVC_32
[<8fe2e0dc>] (memcpy_sz+0x40/0x48) from [<8fe2f337>] (mem_read+0x3b/0x48)
[<8fe2f337>] (mem_read+0x3b/0x48) from [<8fe2bb13>] (cdev_read+0x25/0x2e)
[<8fe2bb13>] (cdev_read+0x25/0x2e) from [<8fe2c15b>] (devfs_read+0x1b/0x1e)
[<8fe2c15b>] (devfs_read+0x1b/0x1e) from [<8fe2df5b>] (__read+0x43/0x5c)
[<8fe2df5b>] (__read+0x43/0x5c) from [<8fe2e61f>] (read+0x2b/0x48)
[<8fe2e61f>] (read+0x2b/0x48) from [<8fe1e4a5>] (do_mem_md+0xc1/0x144)
[<8fe1e4a5>] (do_mem_md+0xc1/0x144) from [<8fe02889>] (execute_command+0x21/0x48)
[<8fe02889>] (execute_command+0x21/0x48) from [<8fe061c1>] (run_list_real+0x549/0x634)
[<8fe061c1>] (run_list_real+0x549/0x634) from [<8fe05b43>] (parse_stream_outer+0xdb/0x174)
[<8fe05b43>] (parse_stream_outer+0xdb/0x174) from [<8fe06435>] (run_shell+0x29/0x54)
[<8fe06435>] (run_shell+0x29/0x54) from [<8fe02889>] (execute_command+0x21/0x48)
[<8fe02889>] (execute_command+0x21/0x48) from [<8fe061c1>] (run_list_real+0x549/0x634)
[<8fe061c1>] (run_list_real+0x549/0x634) from [<8fe05efb>] (run_list_real+0x283/0x634)
[<8fe31e1d>] (unwind_backtrace+0x1/0x64) from [<8fe24e61>] (panic+0x1d/0x34)
[<8fe24e61>] (panic+0x1d/0x34) from [<8fe322c1>] (do_exception+0xd/0x10)
[<8fe322c1>] (do_exception+0xd/0x10) from [<8fe32329>] (do_data_abort+0x21/0x2c)
[<8fe32329>] (do_data_abort+0x21/0x2c) from [<8fe31fe8>] (data_abort+0x48/0x60)
The new behaviour:
barebox at TI AM335x BeagleBone:/ md 0x50000000
50000000: 00000060 00000000 00000000 00000000 `...............
50000010: 00000000 00000001 00000000 00000000 ................
50000020: 00000000 00000000 00000000 00000000 ................
50000030: 00000000 00000000 00000000 00000000 ................
50000040: 00001ff0 400000ac 00000211 00000000 ....... at ........
50000050: 00000a00 00000001 00000000 00000000 ................
50000060: 00000000 00101001 22060514 10057016 ...........".p..
50000070: 010f1111 8f070000 00000f40 00000000 ........ at .......
50000080: 00000000 00000000 00000000 00000000 ................
50000090: 00001000 00101001 22060514 10057016 ...........".p..
500000a0: 010f1111 8f070000 00000f00 XXXXXXXX ................
500000b0: XXXXXXXX XXXXXXXX 00000000 00000000 ................
500000c0: 00001000 00101001 22060514 10057016 ...........".p..
500000d0: 010f1111 8f070000 00000f00 XXXXXXXX ................
500000e0: XXXXXXXX XXXXXXXX 00000000 00000000 ................
500000f0: 00001000 00101001 22060514 10057016 ...........".p..
The current implementation breaks everything except ARM and takes several
shortcuts which need to be implemented more cleanly. Suggestions are very
welcome!
Signed-off-by: Jan Luebbe <jlu at pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
arch/arm/cpu/exceptions.S | 19 +++++++++++++++++++
commands/md.c | 8 ++++++++
common/memory_display.c | 37 ++++++++++++++++++++++++++++++++-----
3 files changed, 59 insertions(+), 5 deletions(-)
diff --git a/arch/arm/cpu/exceptions.S b/arch/arm/cpu/exceptions.S
index 167c8d1..b13e112 100644
--- a/arch/arm/cpu/exceptions.S
+++ b/arch/arm/cpu/exceptions.S
@@ -88,6 +88,21 @@
movs pc, lr
.endm
+ .macro try_data_abort
+ ldr r13, =abort_conf @ check try mode
+ ldr r13, [r13]
+ cmp r13, #0
+ bne no_abort_\@
+ ldr r13, =abort_conf @ disable try mode
+ str r13, [r13]
+ mrs r13, spsr @ read saved CPSR
+ tst r13, #1<<5 @ check Thumb mode
+ subeq lr, #4 @ next ARM instr
+ subne lr, #6 @ next Thumb instr
+ movs pc, lr
+no_abort_\@:
+ .endm
+
.macro get_irq_stack @ setup IRQ stack
ldr sp, IRQ_STACK_START
.endm
@@ -122,6 +137,7 @@ prefetch_abort:
.align 5
data_abort:
+ try_data_abort
get_bad_stack
bad_save_user_regs
bl do_data_abort
@@ -202,5 +218,8 @@ _fiq: .word fiq
.section .data
.align 4
+.global abort_conf
+abort_conf:
+.word abort_conf /* = 0 when enabled, =abort_conf when disabled */
abort_stack:
.space 8
diff --git a/commands/md.c b/commands/md.c
index c1361a6..49b36fd 100644
--- a/commands/md.c
+++ b/commands/md.c
@@ -44,6 +44,7 @@ static int do_mem_md(int argc, char *argv[])
char *filename = "/dev/mem";
int mode = O_RWSIZE_4;
int swab = 0;
+ void *addr;
if (argc < 2)
return COMMAND_ERROR_USAGE;
@@ -65,6 +66,13 @@ static int do_mem_md(int argc, char *argv[])
if (fd < 0)
return 1;
+ addr = memmap(fd, PROT_READ);
+ if (addr != (void *)-1) {
+ ret = memory_display(addr + start, start, size,
+ mode >> O_RWSIZE_SHIFT, swab);
+ goto out;
+ }
+
do {
now = min(size, (loff_t)RW_BUF_SIZE);
r = read(fd, mem_rw_buf, now);
diff --git a/common/memory_display.c b/common/memory_display.c
index c8ae57a..766b8c0 100644
--- a/common/memory_display.c
+++ b/common/memory_display.c
@@ -7,6 +7,7 @@ int memory_display(const void *addr, loff_t offs, unsigned nbytes, int size, int
{
ulong linebytes, i;
u_char *cp;
+ extern volatile int abort_conf;
/* Print the lines.
*
@@ -26,18 +27,44 @@ int memory_display(const void *addr, loff_t offs, unsigned nbytes, int size, int
for (i = 0; i < linebytes; i += size) {
if (size == 4) {
u32 res;
- res = (*uip++ = *((uint *)addr));
+ abort_conf = 0;
+ res = *((uint *)addr);
if (swab)
res = __swab32(res);
- count -= printf(" %08x", res);
+ if (abort_conf) {
+ res = 0xffffffff;
+ count -= printf(" xxxxxxxx");
+ } else {
+ abort_conf = 1;
+ count -= printf(" %08x", res);
+ }
+ *uip++ = res;
} else if (size == 2) {
u16 res;
- res = (*usp++ = *((ushort *)addr));
+ abort_conf = 0;
+ res = *((ushort *)addr);
if (swab)
res = __swab16(res);
- count -= printf(" %04x", res);
+ if (abort_conf) {
+ res = 0xffff;
+ count -= printf(" xxxx");
+ } else {
+ abort_conf = 1;
+ count -= printf(" %04x", res);
+ }
+ *usp++ = res;
} else {
- count -= printf(" %02x", (*ucp++ = *((u_char *)addr)));
+ u8 res;
+ abort_conf = 0;
+ res = *((u_char *)addr);
+ if (abort_conf) {
+ res = 0xff;
+ count -= printf(" xx");
+ } else {
+ abort_conf = 1;
+ count -= printf(" %02x", res);
+ }
+ *ucp++ = res;
}
addr += size;
offs += size;
--
2.1.0
--
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