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authorSamuel Thibault <samuel.thibault@ens-lyon.org>2016-06-09 02:05:44 +0200
committerSamuel Thibault <samuel.thibault@ens-lyon.org>2016-06-09 02:05:52 +0200
commitaf4e2bc8f1b5c450b22c19ff8e06ded02ef08cba (patch)
treed60c240927ffd28d985287ace742f42de0f7e7bf /hurd/debugging
parente25d4ea07b09e7e6df61777988c1fc104f0a538e (diff)
Add more hardcore debugging hints
Diffstat (limited to 'hurd/debugging')
-rw-r--r--hurd/debugging/glibc.mdwn29
-rw-r--r--hurd/debugging/hardware_watchpoint.mdwn96
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*) &regs, &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*) &regs, count);
+ assert(ret == 0);
+ ret = thread_get_state(thread, i386_DEBUG_STATE, (unsigned*) &regs, &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)