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powerpc/xmon: Fix SPR read/write commands and add command to dump SPRs 

xmon has commands for reading and writing SPRs, but they don't work
currently for several reasons. They attempt to synthesize a small
function containing an mfspr or mtspr instruction and call it. However,
the instructions are on the stack, which is usually not executable.
Also, for 64-bit we set up a procedure descriptor, which is fine for the
big-endian ABIv1, but not correct for ABIv2. Finally, the code uses the
infrastructure for catching memory errors, but that only catches data
storage interrupts and machine check interrupts, but a failed
mfspr/mtspr can generate a program interrupt or a hypervisor emulation
assist interrupt, or be a no-op.

Instead of trying to synthesize a function on the fly, this adds two new
functions, xmon_mfspr() and xmon_mtspr(), which take an SPR number as an
argument and read or write the SPR. Because there is no Power ISA
instruction which takes an SPR number in a register, we have to generate
one of each possible mfspr and mtspr instruction, for all 1024 possible
SPRs. Thus we get just over 8k bytes of code for each of xmon_mfspr()
and xmon_mtspr(). However, this 16kB of code pales in comparison to the
> 130kB of PPC opcode tables used by the xmon disassembler.

To catch interrupts caused by the mfspr/mtspr instructions, we add a new
'catch_spr_faults' flag. If an interrupt occurs while it is set, we come
back into xmon() via program_check_interrupt(), _exception() and die(),
see that catch_spr_faults is set and do a longjmp to bus_error_jmp, back
into read_spr() or write_spr().

This adds a couple of other nice features: first, a "Sa" command that
attempts to read and print out the value of all 1024 SPRs. If any mfspr
instruction acts as a no-op, then the SPR is not implemented and not
printed.

Secondly, the Sr and Sw commands detect when an SPR is not
implemented (i.e. mfspr is a no-op) and print a message to that effect
rather than printing a bogus value.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Paul Mackerras 2016-04-13 21:31:24 +10:00 committed by Michael Ellerman
parent f47822078d
commit 31cdd0c39c
3 changed files with 123 additions and 62 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/powerpc/xmon/Makefile
View File

@ -7,7 +7,7 @@ UBSAN_SANITIZE := n
ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
obj-y += xmon.o nonstdio.o
obj-y += xmon.o nonstdio.o spr_access.o
ifdef CONFIG_XMON_DISASSEMBLY
obj-y += ppc-dis.o ppc-opc.o

45
arch/powerpc/xmon/spr_access.S Normal file
View File

@ -0,0 +1,45 @@
#include <asm/ppc_asm.h>
/* unsigned long xmon_mfspr(sprn, default_value) */
_GLOBAL(xmon_mfspr)
ld r5, .Lmfspr_table@got(r2)
b xmon_mxspr
/* void xmon_mtspr(sprn, new_value) */
_GLOBAL(xmon_mtspr)
ld r5, .Lmtspr_table@got(r2)
b xmon_mxspr
/*
* r3 = sprn
* r4 = default or new value
* r5 = table base
*/
xmon_mxspr:
/*
* To index into the table of mxsprs we need:
* i = (sprn & 0x3ff) * 8
* or using rwlinm:
* i = (sprn << 3) & (0x3ff << 3)
*/
rlwinm r3, r3, 3, 0x3ff << 3
add r5, r5, r3
mtctr r5
mr r3, r4 /* put default_value in r3 for mfspr */
bctr
.Lmfspr_table:
spr = 0
.rept 1024
mfspr r3, spr
blr
spr = spr + 1
.endr
.Lmtspr_table:
spr = 0
.rept 1024
mtspr spr, r4
blr
spr = spr + 1
.endr

138
arch/powerpc/xmon/xmon.c
View File

@ -86,6 +86,7 @@ static char tmpstr[128];
static long bus_error_jmp[JMP_BUF_LEN];
static int catch_memory_errors;
static int catch_spr_faults;
static long *xmon_fault_jmp[NR_CPUS];
/* Breakpoint stuff */
@ -147,7 +148,7 @@ void getstring(char *, int);
static void flush_input(void);
static int inchar(void);
static void take_input(char *);
static unsigned long read_spr(int);
static int read_spr(int, unsigned long *);
static void write_spr(int, unsigned long);
static void super_regs(void);
static void remove_bpts(void);
@ -250,6 +251,9 @@ Commands:\n\
sdi # disassemble spu local store for spu # (in hex)\n"
#endif
" S print special registers\n\
Sa print all SPRs\n\
Sr # read SPR #\n\
Sw #v write v to SPR #\n\
t print backtrace\n\
x exit monitor and recover\n\
X exit monitor and don't recover\n"
@ -442,6 +446,12 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
#ifdef CONFIG_SMP
cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, &cpus_in_xmon)) {
/*
* We catch SPR read/write faults here because the 0x700, 0xf60
* etc. handlers don't call debugger_fault_handler().
*/
if (catch_spr_faults)
longjmp(bus_error_jmp, 1);
get_output_lock();
excprint(regs);
printf("cpu 0x%x: Exception %lx %s in xmon, "
@ -1635,89 +1645,87 @@ static void cacheflush(void)
catch_memory_errors = 0;
}
static unsigned long
read_spr(int n)
extern unsigned long xmon_mfspr(int spr, unsigned long default_value);
extern void xmon_mtspr(int spr, unsigned long value);
static int
read_spr(int n, unsigned long *vp)
{
unsigned int instrs[2];
unsigned long (*code)(void);
unsigned long ret = -1UL;
#ifdef CONFIG_PPC64
unsigned long opd[3];
opd[0] = (unsigned long)instrs;
opd[1] = 0;
opd[2] = 0;
code = (unsigned long (*)(void)) opd;
#else
code = (unsigned long (*)(void)) instrs;
#endif
/* mfspr r3,n; blr */
instrs[0] = 0x7c6002a6 + ((n & 0x1F) << 16) + ((n & 0x3e0) << 6);
instrs[1] = 0x4e800020;
store_inst(instrs);
store_inst(instrs+1);
int ok = 0;
if (setjmp(bus_error_jmp) == 0) {
catch_memory_errors = 1;
catch_spr_faults = 1;
sync();
ret = code();
ret = xmon_mfspr(n, *vp);
sync();
/* wait a little while to see if we get a machine check */
__delay(200);
n = size;
*vp = ret;
ok = 1;
}
catch_spr_faults = 0;
return ret;
return ok;
}
static void
write_spr(int n, unsigned long val)
{
unsigned int instrs[2];
unsigned long (*code)(unsigned long);
#ifdef CONFIG_PPC64
unsigned long opd[3];
opd[0] = (unsigned long)instrs;
opd[1] = 0;
opd[2] = 0;
code = (unsigned long (*)(unsigned long)) opd;
#else
code = (unsigned long (*)(unsigned long)) instrs;
#endif
instrs[0] = 0x7c6003a6 + ((n & 0x1F) << 16) + ((n & 0x3e0) << 6);
instrs[1] = 0x4e800020;
store_inst(instrs);
store_inst(instrs+1);
if (setjmp(bus_error_jmp) == 0) {
catch_memory_errors = 1;
catch_spr_faults = 1;
sync();
code(val);
xmon_mtspr(n, val);
sync();
/* wait a little while to see if we get a machine check */
__delay(200);
n = size;
} else {
printf("SPR 0x%03x (%4d) Faulted during write\n", n, n);
}
catch_spr_faults = 0;
}
static unsigned long regno;
extern char exc_prolog;
extern char dec_exc;
static void dump_one_spr(int spr, bool show_unimplemented)
{
unsigned long val;
val = 0xdeadbeef;
if (!read_spr(spr, &val)) {
printf("SPR 0x%03x (%4d) Faulted during read\n", spr, spr);
return;
}
if (val == 0xdeadbeef) {
/* Looks like read was a nop, confirm */
val = 0x0badcafe;
if (!read_spr(spr, &val)) {
printf("SPR 0x%03x (%4d) Faulted during read\n", spr, spr);
return;
}
if (val == 0x0badcafe) {
if (show_unimplemented)
printf("SPR 0x%03x (%4d) Unimplemented\n", spr, spr);
return;
}
}
printf("SPR 0x%03x (%4d) = 0x%lx\n", spr, spr, val);
}
static void super_regs(void)
{
int cmd;
unsigned long val;
int spr;
cmd = skipbl();
if (cmd == '\n') {
switch (cmd) {
case '\n': {
unsigned long sp, toc;
asm("mr %0,1" : "=r" (sp) :);
asm("mr %0,2" : "=r" (toc) :);
@ -1730,21 +1738,29 @@ static void super_regs(void)
mfspr(SPRN_DEC), mfspr(SPRN_SPRG2));
printf("sp = "REG" sprg3= "REG"\n", sp, mfspr(SPRN_SPRG3));
printf("toc = "REG" dar = "REG"\n", toc, mfspr(SPRN_DAR));
return;
}
scanhex(&regno);
switch (cmd) {
case 'w':
val = read_spr(regno);
case 'w': {
unsigned long val;
scanhex(&regno);
val = 0;
read_spr(regno, &val);
scanhex(&val);
write_spr(regno, val);
/* fall through */
case 'r':
printf("spr %lx = %lx\n", regno, read_spr(regno));
dump_one_spr(regno, true);
break;
}
case 'r':
scanhex(&regno);
dump_one_spr(regno, true);
break;
case 'a':
/* dump ALL SPRs */
for (spr = 1; spr < 1024; ++spr)
dump_one_spr(spr, false);
break;
}
scannl();
}