On Tue, Oct 25, 2016 at 11:07:38AM -0700, Richard Henderson wrote: > On 10/25/2016 01:26 AM, Michael Cree wrote: > > And while I mention gdb, it no longer works on Alpha since version > > 7.10. Richard, would you be able to take a look at the bug report: > > https://sourceware.org/bugzilla/show_bug.cgi?id=19061 > > In the PR, Pedro has exactly the right pointer to the problem. > > >From arch/alpha/kernel/traps.c: > > info.si_signo = SIGTRAP; > info.si_errno = 0; > info.si_code = TRAP_BRKPT; > info.si_trapno = 0; > info.si_addr = (void __user *) regs->pc; > > if (ptrace_cancel_bpt(current)) { > regs->pc -= 4; /* make pc point to former bpt */ > } > > So we report the same si_code for executing a breakpoint insn inserted by gdb, > and a "hardware" breakpoint managed by the kernel. But for the later, we > already back up the PC. > > So gdb winds up backing up the PC twice. > > This ought to be fixed by using TRAP_HWBKPT (4) for the ptrace_cancel_bpt case, > but telling gdb about the issue in gdb/nat/linux-ptrace.c like so: > > #elif defined __alpha__ > # define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == TRAP_BRKPT) > # define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_BRKPT || (X) == TRAP_HWBKPT) > > which looks confusing, but does get checked: > > if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code) > && GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code)) > { > /* The si_code is ambiguous on this arch -- check debug > registers. */ > if (!check_stopped_by_watchpoint (lp)) > lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT; > > but at the moment the default definition of GDB_ARCH_IS_TRAP_HWBKPT is always > false for alpha. By saying "This ought to be fixed by [...] but at the moment [...]" are you saying that the fix provided above will not work? Indeed, it doesn't work: I tried it and just about every test in the gdb test suite still fails. For example: Running /home/mjc/toolchain/gdb-build/gdb/testsuite/../../../binutils-gdb/gdb/testsuite/gdb.base/break.exp ... FAIL: gdb.base/break.exp: run until function breakpoint (timeout) FAIL: gdb.base/break.exp: list marker1 (timeout) FAIL: gdb.base/break.exp: break lineno (timeout) FAIL: gdb.base/break.exp: delete $bpnum (timeout) FAIL: gdb.base/break.exp: run until breakpoint set at a line number (timeout) FAIL: gdb.base/break.exp: run until file:function(6) breakpoint (timeout) Cheers Michael. -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
