diff options
Diffstat (limited to 'hurd/debugging')
| -rw-r--r-- | hurd/debugging/glibc.mdwn | 29 | ||||
| -rw-r--r-- | hurd/debugging/hardware_watchpoint.mdwn | 96 |
2 files changed, 125 insertions, 0 deletions
diff --git a/hurd/debugging/glibc.mdwn b/hurd/debugging/glibc.mdwn index dfc4c1c6..086cffff 100644 --- a/hurd/debugging/glibc.mdwn +++ b/hurd/debugging/glibc.mdwn @@ -64,6 +64,35 @@ or of just one subdir with for instance: --- +In some cases, printing to stdout/stderr is problematic. One can use a kernel +with kdb enabled, and `mach_print` to get messages on the console: + + #include <mach/mach_traps.h> + ... + mach_print("foo\n"); + +If your `mach_traps.h` does not have the declaration, use: + + extern void mach_print(const char *s); + +This call does not support any formatting. You can use this kind of helper to +format a message before passing to gnumach: + + #include <mach/mach_traps.h> + #include <stdio.h> + + static void myprintf(const char *fmt, ...) + { + va_list ap; + char buf[1024]; + va_start(ap, fmt); + vsnprintf(buf, sizeof(buf), fmt, ap); + mach_print(buf); + va_end(ap); + } + +--- + If you've been doing simple changes to glibc functions that end up in `libc.so`, you may test them like this (like for a `strerror_l` implementation in this case): diff --git a/hurd/debugging/hardware_watchpoint.mdwn b/hurd/debugging/hardware_watchpoint.mdwn new file mode 100644 index 00000000..f7d153c8 --- /dev/null +++ b/hurd/debugging/hardware_watchpoint.mdwn @@ -0,0 +1,96 @@ +[[!meta copyright="Copyright © 2016 Free Software +Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +Hardware watchpoints work in gdb, provided that you give an absolute address and a size which is 1, 2, 4, or 8: + + (gdb) watch *(unsigned *) 0x1234 + Hardware watchpoint 2: * (unsigned*) 0x1234 + +One can also trigger this from an application, by using the following function: + + #include <mach/machine/thread_status.h> + #include <mach/mach_interface.h> + #include <mach/mach_traps.h> + #include <sys/types.h> + #include <stdint.h> + #include <stdio.h> + #include <signal.h> + #include <assert.h> + + void set_hardware_watchpoint(mach_port_t thread, int num, int type, void *addr, size_t len) + { + struct i386_debug_state regs; + + int persistence = 3; + len = len - 1; + if (len == 7) + len = 2; + + mach_msg_type_number_t count = i386_DEBUG_STATE_COUNT; + int ret = thread_get_state(thread, i386_DEBUG_STATE, (unsigned*) ®s, &count); + assert(ret == 0); + + regs.dr[num] = (uintptr_t) addr; + regs.dr[7] &= ~(0xfUL << (4*num+16)) & ~(0x3UL << (2*num)); + if (addr) + regs.dr[7] |= (((len << 2) | type) << (4*num+16)) | (persistence << (2*num)); + + ret = thread_set_state(thread, i386_DEBUG_STATE, (unsigned*) ®s, count); + assert(ret == 0); + ret = thread_get_state(thread, i386_DEBUG_STATE, (unsigned*) ®s, &count); + assert(ret == 0); + } + + .... + set_hardware_watchpoint(mach_thread_self(), 0, 1, &x, sizeof(x)); + .... + set_hardware_watchpoint(mach_thread_self(), 0, 0, 0, 0); + +Up to 4 watchpoints can be set, `num` determines which one should be set. + +`type` can be 0 (`I386_DB_TYPE_X`), 1 (`I386_DB_TYPE_W`), or 3 (`I386_DB_TYPE_RW`) + +Note that only the specified thread will have the breakpoint. + +Note that only recent versions of gnumach allows to set hardware watchpoints for +the current thread. + +These watchpoints will trigger a SIGTRAP signal. If one only wants to see the +events, one can use this gnumach patch: + + diff --git a/i386/i386/trap.c b/i386/i386/trap.c + index 6470504..e3b5864 100644 + --- a/i386/i386/trap.c + +++ b/i386/i386/trap.c + @@ -395,6 +395,23 @@ printf("user trap %d error %d sub %08x\n", type, code, subcode); + return 0; + } + #endif /* MACH_KDB */ + + + + printf("user debug trap %p\n", regs->eip); + + vm_offset_t addr; + + if (get_dr6() & 0x1) + + addr = get_dr0(); + + if (get_dr6() & 0x2) + + addr = get_dr1(); + + if (get_dr6() & 0x4) + + addr = get_dr2(); + + if (get_dr6() & 0x8) + + addr = get_dr3(); + + unsigned long data; + + db_read_bytes(addr, 4, &data, current_task()); + + printf("hit %lx at %p\n", data, addr); + + set_dr6(0); + + return 0; + + + /* Make the content of the debug status register (DR6) + available to user space. */ + if (thread->pcb) |