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powerpc/kgdb: add kgdb_arch_set/remove_breakpoint() 

Generic implementation fails to remove breakpoints after init
when CONFIG_STRICT_KERNEL_RWX is selected:

[   13.251285] KGDB: BP remove failed: c001c338
[   13.259587] kgdbts: ERROR PUT: end of test buffer on 'do_fork_test' line 8 expected OK got $E14#aa
[   13.268969] KGDB: re-enter exception: ALL breakpoints killed
[   13.275099] CPU: 0 PID: 1 Comm: init Not tainted 4.18.0-g82bbb913ffd8 #860
[   13.282836] Call Trace:
[   13.285313] [c60e1ba0] [c0080ef0] kgdb_handle_exception+0x6f4/0x720 (unreliable)
[   13.292618] [c60e1c30] [c000e97c] kgdb_handle_breakpoint+0x3c/0x98
[   13.298709] [c60e1c40] [c000af54] program_check_exception+0x104/0x700
[   13.305083] [c60e1c60] [c000e45c] ret_from_except_full+0x0/0x4
[   13.310845] [c60e1d20] [c02a22ac] run_simple_test+0x2b4/0x2d4
[   13.316532] [c60e1d30] [c0081698] put_packet+0xb8/0x158
[   13.321694] [c60e1d60] [c00820b4] gdb_serial_stub+0x230/0xc4c
[   13.327374] [c60e1dc0] [c0080af8] kgdb_handle_exception+0x2fc/0x720
[   13.333573] [c60e1e50] [c000e928] kgdb_singlestep+0xb4/0xcc
[   13.339068] [c60e1e70] [c000ae1c] single_step_exception+0x90/0xac
[   13.345100] [c60e1e80] [c000e45c] ret_from_except_full+0x0/0x4
[   13.350865] [c60e1f40] [c000e11c] ret_from_syscall+0x0/0x38
[   13.356346] Kernel panic - not syncing: Recursive entry to debugger

This patch creates powerpc specific version of
kgdb_arch_set_breakpoint() and kgdb_arch_remove_breakpoint()
using patch_instruction()

Fixes: 1e0fc9d1eb ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
hifive-unleashed-5.1
Christophe Leroy 2018-09-18 09:26:03 +00:00 committed by Michael Ellerman
parent 6beb3381b1
commit fb978ca207
2 changed files with 39 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/powerpc/include/asm/kgdb.h
View File

@ -26,9 +26,12 @@
#define BREAK_INSTR_SIZE 4
#define BUFMAX ((NUMREGBYTES * 2) + 512)
#define OUTBUFMAX ((NUMREGBYTES * 2) + 512)
#define BREAK_INSTR 0x7d821008 /* twge r2, r2 */
static inline void arch_kgdb_breakpoint(void)
{
asm(".long 0x7d821008"); /* twge r2, r2 */
asm(stringify_in_c(.long BREAK_INSTR));
}
#define CACHE_FLUSH_IS_SAFE 1
#define DBG_MAX_REG_NUM 70

43
arch/powerpc/kernel/kgdb.c
View File

@ -24,6 +24,7 @@
#include <asm/processor.h>
#include <asm/machdep.h>
#include <asm/debug.h>
#include <asm/code-patching.h>
#include <linux/slab.h>
/*
@ -144,7 +145,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
if (kgdb_handle_exception(1, SIGTRAP, 0, regs) != 0)
return 0;
if (*(u32 *) (regs->nip) == *(u32 *) (&arch_kgdb_ops.gdb_bpt_instr))
if (*(u32 *)regs->nip == BREAK_INSTR)
regs->nip += BREAK_INSTR_SIZE;
return 1;
@ -441,16 +442,42 @@ int kgdb_arch_handle_exception(int vector, int signo, int err_code,
return -1;
}
int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
{
int err;
unsigned int instr;
unsigned int *addr = (unsigned int *)bpt->bpt_addr;
err = probe_kernel_address(addr, instr);
if (err)
return err;
err = patch_instruction(addr, BREAK_INSTR);
if (err)
return -EFAULT;
*(unsigned int *)bpt->saved_instr = instr;
return 0;
}
int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
{
int err;
unsigned int instr = *(unsigned int *)bpt->saved_instr;
unsigned int *addr = (unsigned int *)bpt->bpt_addr;
err = patch_instruction(addr, instr);
if (err)
return -EFAULT;
return 0;
}
/*
* Global data
*/
struct kgdb_arch arch_kgdb_ops = {
#ifdef __LITTLE_ENDIAN__
.gdb_bpt_instr = {0x08, 0x10, 0x82, 0x7d},
#else
.gdb_bpt_instr = {0x7d, 0x82, 0x10, 0x08},
#endif
};
struct kgdb_arch arch_kgdb_ops;
static int kgdb_not_implemented(struct pt_regs *regs)
{