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Date: Wed, 17 Apr 2013 22:02:06 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>, Arnaldo Carvalho de Melo <acme@...stprotocols.net>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>, Corey Ashford <cjashfor@...ux.vnet.ibm.com>, Vince Weaver <vincent.weaver@...ne.edu>, Stephane Eranian <eranian@...gle.com> Subject: Re: [PATCH 1/6] signal x86: Propage RF EFLAGS bit throught the signal restore call On 04/16, Oleg Nesterov wrote: > > On 04/16, Frederic Weisbecker wrote: > > > > On Sun, Mar 10, 2013 at 07:41:06PM +0100, Jiri Olsa wrote: > > > Adding RF EFLAGS bit to be restored on return from signal from > > > the original register context before the signal was entered. > > > > > > This will prevent the RF flag to disappear when returning > > > from exception due to the signal handler being executed. > > > > So that happens if, say, we get a breakpoint exception and then we > > run a signal handler before returning to the ip that triggered the > > breakpoint? > > Afaics these changes (1 and 2) should fix the bug. > > Suppose that the first insn in the signal handler should trigger > another bp, we should clear X86_EFLAGS_RF (2/6). > > Otoh, we should restore it when we return to the original insn > which triggered the trap to avoid another trap. I applied 1 and 2, and this fixes the test-case below. > But. it seems that we have yet another problem? Suppose that > the signal handler does siglongjmp() and jumps to yet another > insn which should trigger the trap? Argh. Sorry for confusion. I tried to say that the signal handler can play with sigcontext->ip before sigreturn(). But probably we can ignore this. Oleg. ------------------------------------------------------------------------------- #define _GNU_SOURCE 1 #include <stdio.h> #include <unistd.h> #include <sys/ptrace.h> #include <sys/debugreg.h> #include <sys/user.h> #include <sys/wait.h> #include <assert.h> #include <assert.h> #include <stddef.h> #define DR_GLOBAL_ENABLE 0x2 #define DR_LOCAL_ENABLE 0x1 unsigned long encode_dr7(int drnum, int enable, unsigned int type, unsigned int len) { unsigned long dr7; dr7 = ((len | type) & 0xf) << (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE); if (enable) dr7 |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)); return dr7; } int write_dr(int pid, int dr, unsigned long val) { return ptrace(PTRACE_POKEUSER, pid, offsetof (struct user, u_debugreg[dr]), val); } #define GET_REG(pid, reg) \ ptrace(PTRACE_PEEKUSER, (pid), \ offsetof(struct user, regs.reg), 0) void *get_ip(int pid) { return (void*)GET_REG(pid, rip); } void func(void) { printf("bp_1 passed\n"); } void sigh(int sig) { printf("bp_2 passed\n"); } int main(void) { int pid, stat; unsigned long dr7; pid = fork(); if (!pid) { assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0); kill(getpid(), SIGHUP); signal(SIGINT, sigh); func(); return 0x13; } assert(pid == waitpid(-1, &stat, 0)); assert(WSTOPSIG(stat) == SIGHUP); assert(write_dr(pid, 0, (long)func) == 0); assert(write_dr(pid, 1, (long)sigh) == 0); dr7 = 0; dr7 |= encode_dr7(0, 1, DR_RW_EXECUTE, DR_LEN_1); dr7 |= encode_dr7(1, 1, DR_RW_EXECUTE, DR_LEN_1); assert(write_dr(pid, 7, dr7) == 0); assert(ptrace(PTRACE_CONT, pid, 0,0) == 0); assert(pid == waitpid(-1, &stat, 0)); assert(WSTOPSIG(stat) == SIGTRAP); assert(get_ip(pid) == func); kill(pid, SIGINT); assert(ptrace(PTRACE_CONT, pid, 0,0) == 0); assert(pid == waitpid(-1, &stat, 0)); assert(WSTOPSIG(stat) == SIGINT); assert(ptrace(PTRACE_CONT, pid, 0,SIGINT) == 0); assert(pid == waitpid(-1, &stat, 0)); assert(WSTOPSIG(stat) == SIGTRAP); assert(get_ip(pid) == sigh); assert(ptrace(PTRACE_CONT, pid, 0,0) == 0); assert(pid == waitpid(-1, &stat, 0)); assert(stat == 0x1300); return 0; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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