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this patch adds access to the debug breakpoints to

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the kernel. They are not used atm, but having them in trunk allows them
to be easily used when needed. To set a breakpoint that triggers when
the variable foo is written to (the most common use case), one calls:

breakpoint_set(vir2phys((vir_bytes) &foo), 0,
  BREAKPOINT_FLAG_MODE_GLOBAL |
  BREAKPOINT_FLAG_RW_WRITE |
  BREAKPOINT_FLAG_LEN_4);

It can later be disabled using:

breakpoint_set(vir2phys((vir_bytes) &foo), 0,
  BREAKPOINT_FLAG_MODE_OFF);

There are some limitations:

- There are at most four breakpoints (hardware limit); the index of the
  breakpoint (0-3) is specified as the second parameter of
  breakpoint_set.

- The breakpoint exception in the kernel is not handled and causes a
  panic; it would be reasonably easy to change this by inspecing DR6,
  printing a message, disabling the breakpoint and continuing. However,
  in my experience even just a panic can be very useful.

- Breakpoints can be set only in the part of the address space that is
  in every page table. It is useful for the kernel, but to use this for
  user processes would require saving and restoring the debug registers
  as part of the context switch. Although the CPU provides support for
  local breakpoints (I implemened this as BREAKPOINT_FLAG_LOCAL) they
  only work if task switching is used.
This commit is contained in:
Erik van der Kouwe 2010-03-19 19:15:20 +00:00
parent 19ff96081c
commit b42c66ed10
8 changed files with 159 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
commands/i386/gas2ack/asm86.c
View File

@ -75,6 +75,7 @@ int isregister(const char *name)
"eax", "ebx", "ecx", "edx", "esi", "edi", "ebp", "esp",
"cs", "ds", "es", "fs", "gs", "ss",
"cr0", "cr1", "cr2", "cr3", "cr4",
"dr0", "dr1", "dr2", "dr3", "dr6", "dr7",
"st",
};
int reg;

4
commands/i386/gas2ack/gas2ack.c
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@ -1,7 +1,7 @@
/* asmconv 1.11 - convert 80X86 assembly Author: Kees J. Bot
/* asmconv 1.12 - convert 80X86 assembly Author: Kees J. Bot
* 24 Dec 1993
*/
static char version[] = "1.11";
static char version[] = "1.12";
#define nil 0
#include <stdio.h>

2
docs/UPDATING
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@ -70,4 +70,6 @@
The hello driver (/dev/hello) added to the distribution:
# cd /usr/src/commands/scripts && make clean install
# cd /dev && MAKEDEV hello
20100318:
Gas2ack updates: Run 'make install' in commands/i386/gas2ack

7
kernel/arch/i386/Makefile
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@ -9,7 +9,9 @@ ARCHAR=$(ARCH).a
# by an upper level Makefile.
OBJS= arch_do_vmctl.o \
breakpoints.o \
clock.o \
debugreg.o \
do_int86.o \
do_iopenable.o \
do_readbios.o \
@ -56,6 +58,11 @@ apic_asm.o: apic_asm.S
gas2ack -u $@.tmp $@.s
$(CC) $(CFLAGS) -c -o $@ $@.s
debugreg.o: debugreg.S
$(CC) $(CFLAGS) -E -D__ASSEMBLY__ -o $@.tmp $<
gas2ack -u $@.tmp $@.s
$(CC) $(CFLAGS) -c -o $@ $@.s
$(HEAD): mpx386.o
cp $< $@

60
kernel/arch/i386/breakpoints.c Normal file
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@ -0,0 +1,60 @@
#include "../../kernel.h"
#include "proto.h"
#include "debugreg.h"
int breakpoint_set(phys_bytes linaddr, int bp, int flags)
{
u32_t dr7, dr7flags;
if (bp >= BREAKPOINT_COUNT)
return EINVAL;
/* convert flags */
dr7flags = 0;
switch (flags & BREAKPOINT_FLAG_RW_MASK) {
case BREAKPOINT_FLAG_RW_EXEC: dr7flags |= DR7_RW_EXEC(bp); break;
case BREAKPOINT_FLAG_RW_WRITE: dr7flags |= DR7_RW_WRITE(bp); break;
case BREAKPOINT_FLAG_RW_RW: dr7flags |= DR7_RW_RW(bp); break;
default: return EINVAL;
}
switch (flags & BREAKPOINT_FLAG_LEN_MASK) {
case BREAKPOINT_FLAG_LEN_1: dr7flags |= DR7_LN_1(bp); break;
case BREAKPOINT_FLAG_LEN_2: dr7flags |= DR7_LN_2(bp); break;
case BREAKPOINT_FLAG_LEN_4: dr7flags |= DR7_LN_4(bp); break;
default: return EINVAL;
}
switch (flags & BREAKPOINT_FLAG_MODE_MASK) {
case BREAKPOINT_FLAG_MODE_OFF: break;
case BREAKPOINT_FLAG_MODE_LOCAL: dr7flags |= DR7_L(bp); break;
case BREAKPOINT_FLAG_MODE_GLOBAL: dr7flags |= DR7_G(bp); break;
default: return EINVAL;
}
/* disable breakpoint before setting address */
dr7 = st_dr7();
dr7 &= ~(DR7_L(bp) | DR7_G(bp) | DR7_RW_MASK(bp) | DR7_LN_MASK(bp));
printf("ld_dr7(0x%x)\n",dr7);
ld_dr7(dr7);
/* need to set new breakpoint? */
if ((flags & BREAKPOINT_FLAG_MODE_MASK) == BREAKPOINT_FLAG_MODE_OFF)
return 0;
/* set breakpoint address */
switch (bp) {
case 0: ld_dr0(linaddr); break;
case 1: ld_dr1(linaddr); break;
case 2: ld_dr2(linaddr); break;
case 3: ld_dr3(linaddr); break;
default: panic(__FILE__, "invalid breakpoint index", __LINE__);
}
printf("ld_dr%d(0x%x, 0x%x)\n",bp,linaddr);
/* set new flags */
dr7 |= dr7flags;
ld_dr7(dr7);
printf("ld_dr7(0x%x)\n",dr7);
return 0;
}

26
kernel/arch/i386/debugreg.S Normal file
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@ -0,0 +1,26 @@
.text
#define LD_ST_REG(reg) ;\
.globl ld_##reg ;\
.globl st_##reg ;\
;\
ld_##reg: ;\
mov 4(%esp), %eax ;\
mov %eax, %reg ;\
ret ;\
;\
st_##reg: ;\
mov %reg, %eax ;\
ret
/*
* void ld_dr0(u32_t value)
* u32_t st_dr0(void)
*/
LD_ST_REG(dr0)
LD_ST_REG(dr1)
LD_ST_REG(dr2)
LD_ST_REG(dr3)
LD_ST_REG(dr6)
LD_ST_REG(dr7)

44
kernel/arch/i386/debugreg.h Normal file
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@ -0,0 +1,44 @@
#ifndef __DEBUGREG_H__
#define __DEBUGREG_H__
/* DR6: status flags */
#define DR6_B(bp) (1 << (bp)) /* breakpoint was triggered */
#define DR6_BD (1 << 13) /* debug register access detected */
#define DR6_BS (1 << 14) /* single step */
#define DR6_BT (1 << 15) /* task switch */
/* DR7: control flags */
#define DR7_L(bp) (1 << (2*(bp))) /* breakpoint armed locally */
#define DR7_G(bp) (1 << (1+2*(bp))) /* breakpoint armed globally */
#define DR7_LE (1 << 8) /* exact local breakpoints */
#define DR7_GE (1 << 9) /* exact global breakpoints */
#define DR7_GD (1 << 13) /* detect debug reg movs */
#define DR7_RW_MASK(bp) (3 << (16+4*(bp)))
#define DR7_RW_EXEC(bp) (0 << (16+4*(bp))) /* execute */
#define DR7_RW_WRITE(bp) (1 << (16+4*(bp))) /* write */
#define DR7_RW_IO(bp) (2 << (16+4*(bp))) /* IO */
#define DR7_RW_RW(bp) (3 << (16+4*(bp))) /* read or write */
#define DR7_LN_MASK(bp) (3 << (18+4*(bp)))
#define DR7_LN_1(bp) (0 << (18+4*(bp))) /* 1 byte */
#define DR7_LN_2(bp) (1 << (18+4*(bp))) /* 2 bytes */
#define DR7_LN_8(bp) (2 << (18+4*(bp))) /* 8 bytes */
#define DR7_LN_4(bp) (3 << (18+4*(bp))) /* 4 bytes */
/* debugreg.S */
void ld_dr0(u32_t value);
void ld_dr1(u32_t value);
void ld_dr2(u32_t value);
void ld_dr3(u32_t value);
void ld_dr6(u32_t value);
void ld_dr7(u32_t value);
u32_t st_dr0(void);
u32_t st_dr1(void);
u32_t st_dr2(void);
u32_t st_dr3(void);
u32_t st_dr6(void);
u32_t st_dr7(void);
#endif /* __DEBUGREG_H__ */

17
kernel/arch/i386/proto.h
View File

@ -156,6 +156,23 @@ _PROTOTYPE(void __copy_msg_from_user_end, (void));
_PROTOTYPE(void __copy_msg_to_user_end, (void));
_PROTOTYPE(void __user_copy_msg_pointer_failure, (void));
/* breakpoints.c */
#define BREAKPOINT_COUNT 4
#define BREAKPOINT_FLAG_RW_MASK (3 << 0)
#define BREAKPOINT_FLAG_RW_EXEC (0 << 0)
#define BREAKPOINT_FLAG_RW_WRITE (1 << 0)
#define BREAKPOINT_FLAG_RW_RW (2 << 0)
#define BREAKPOINT_FLAG_LEN_MASK (3 << 2)
#define BREAKPOINT_FLAG_LEN_1 (0 << 2)
#define BREAKPOINT_FLAG_LEN_2 (1 << 2)
#define BREAKPOINT_FLAG_LEN_4 (2 << 2)
#define BREAKPOINT_FLAG_MODE_MASK (3 << 4)
#define BREAKPOINT_FLAG_MODE_OFF (0 << 4)
#define BREAKPOINT_FLAG_MODE_LOCAL (1 << 4)
#define BREAKPOINT_FLAG_MODE_GLOBAL (2 << 4)
_PROTOTYPE(int breakpoint_set, (phys_bytes linaddr, int index, int flags));
/* functions defined in architecture-independent kernel source. */
#include "../../proto.h"