From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31826 invoked by alias); 13 Jun 2011 15:56:19 -0000 Received: (qmail 31804 invoked by uid 22791); 13 Jun 2011 15:56:17 -0000 X-SWARE-Spam-Status: No, hits=-1.9 required=5.0 tests=AWL,BAYES_00,TW_XF,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from sibelius.xs4all.nl (HELO glazunov.sibelius.xs4all.nl) (83.163.83.176) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 13 Jun 2011 15:56:01 +0000 Received: from glazunov.sibelius.xs4all.nl (kettenis@localhost [127.0.0.1]) by glazunov.sibelius.xs4all.nl (8.14.3/8.14.3) with ESMTP id p5DFtwgx030500 for ; Mon, 13 Jun 2011 17:55:58 +0200 (CEST) Received: (from kettenis@localhost) by glazunov.sibelius.xs4all.nl (8.14.3/8.14.3/Submit) id p5DFtucc019690; Mon, 13 Jun 2011 17:55:56 +0200 (CEST) Date: Mon, 13 Jun 2011 15:56:00 -0000 Message-Id: <201106131555.p5DFtucc019690@glazunov.sibelius.xs4all.nl> From: Mark Kettenis To: gdb-patches@sourceware.org Subject: [RFC] i386 PLT stub unwinder Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2011-06/txt/msg00162.txt.bz2 Jan's mail about DWARF CFI for PLT stubs prompted me to write an undinder for the PLT stubs as defined by the i386 ABI. With this change I can step through the PLT stubs and always have a proper backtrace. The reason that this is an RFC, is that I'm a little bit confused about the TRY_CATCH stuff that was introduced in some of the i386 unwinders by Pedro. It isn't entirely clear to me when that is needed. Unwinding the PC should always succeed at this point, since the sniffers already rely on that. And unwinding the stack pointer needs to be working as well, otherwise unwinding the PC will never have worked. So I don't think I need to worry about unavailable registers here. 2011-06-12 Mark Kettenis * i386-tdep.c (i386_plt0_stub_insns, i386_plt_stub_insns) (i386_pic_plt0_stub_insns, i386_pic_plt_stub_insns): New variables. (i386_plt_stub_frame_cache, i386_plt_stub_frame_this_id) (i386_plt_stub_frame_prev_register, i386_plt_stub_frame_sniffer): New functions. (i386_plt_stub_frame_unwind): New variable. (i386_elf_init_abi): Append PLT stub unwinder. Index: i386-tdep.c =================================================================== RCS file: /cvs/src/src/gdb/i386-tdep.c,v retrieving revision 1.334 diff -u -p -r1.334 i386-tdep.c --- i386-tdep.c 12 Jun 2011 20:46:11 -0000 1.334 +++ i386-tdep.c 13 Jun 2011 15:43:26 -0000 @@ -2070,6 +2070,200 @@ static const struct frame_unwind i386_st }; +/* PLT stubs. */ + +struct i386_insn i386_plt0_stub_insns[] = +{ + /* `pushl imm32' */ + { 6, { 0xff, 0x35 }, { 0xff, 0xff } }, + + /* `jmp *disp32' */ + { 6, { 0xff, 0x25 }, { 0xff, 0xff } }, + + {0} +}; + +struct i386_insn i386_plt_stub_insns[] = +{ + /* `jmp *disp32' */ + { 6, { 0xff, 0x25 }, { 0xff, 0xff } }, + + /* `pushl imm32' */ + { 5, { 0x68 }, { 0xff } }, + + /* `jmp rel32' */ + { 5, { 0xe9 }, { 0xff } }, + + {0} +}; + +struct i386_insn i386_pic_plt0_stub_insns[] = +{ + /* `pushl imm32' */ + { 6, { 0xff, 0xb3, 4, 0, 0, 0 }, { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } }, + + /* `jmp *imm32' */ + { 6, { 0xff, 0xa3, 8, 0, 0, 0 }, { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } }, + + {0} +}; + +struct i386_insn i386_pic_plt_stub_insns[] = +{ + /* `jmp *disp32(%ebx)' */ + { 6, { 0xff, 0xa3 }, { 0xff, 0xff } }, + + /* `pushl imm32' */ + { 5, { 0x68 }, { 0xff } }, + + /* `jmp rel32' */ + { 5, { 0xe9 }, { 0xff } }, + + {0} +}; + +static struct i386_frame_cache * +i386_plt_stub_frame_cache (struct frame_info *this_frame, void **this_cache) +{ + struct i386_frame_cache *cache; + struct i386_insn *insn; + LONGEST sp_offset = -4; + CORE_ADDR pc, sp; + int i; + + if (*this_cache) + return *this_cache; + + cache = i386_alloc_frame_cache (); + *this_cache = cache; + + pc = get_frame_pc (this_frame); + if (i386_match_insn_block (pc, i386_plt_stub_insns)) + { + insn = i386_match_insn (pc, i386_plt_stub_insns); + + for (i = 0; i < ARRAY_SIZE(i386_plt_stub_insns); i++) + { + if (insn == &i386_plt_stub_insns[i]) + break; + + pc -= i386_plt_stub_insns[i].len; + } + + if (insn == &i386_plt_stub_insns[2]) + cache->sp_offset = 0; + } + else if (i386_match_insn_block (pc, i386_plt0_stub_insns)) + { + insn = i386_match_insn (pc, i386_plt0_stub_insns); + + for (i = 0; i < ARRAY_SIZE(i386_plt0_stub_insns); i++) + { + if (insn == &i386_plt0_stub_insns[i]) + break; + + pc -= i386_plt0_stub_insns[i].len; + } + + if (insn == &i386_plt0_stub_insns[0]) + cache->sp_offset = 0; + else + cache->sp_offset = 4; + } + else if (i386_match_insn_block (pc, i386_pic_plt_stub_insns)) + { + insn = i386_match_insn (pc, i386_pic_plt_stub_insns); + + for (i = 0; i < ARRAY_SIZE(i386_pic_plt_stub_insns); i++) + { + if (insn == &i386_pic_plt_stub_insns[i]) + break; + + pc -= i386_pic_plt_stub_insns[i].len; + } + + if (insn == &i386_pic_plt_stub_insns[2]) + cache->sp_offset = 0; + } + else if (i386_match_insn_block (pc, i386_pic_plt0_stub_insns)) + { + insn = i386_match_insn (pc, i386_pic_plt0_stub_insns); + + for (i = 0; i < ARRAY_SIZE(i386_pic_plt0_stub_insns); i++) + { + if (insn == &i386_pic_plt0_stub_insns[i]) + break; + + pc -= i386_pic_plt0_stub_insns[i].len; + } + + if (insn == &i386_pic_plt0_stub_insns[0]) + cache->sp_offset = 0; + else + cache->sp_offset = 4; + } + + cache->pc = pc; + + sp = get_frame_register_unsigned (this_frame, I386_ESP_REGNUM); + cache->base = sp + cache->sp_offset; + cache->saved_sp = cache->base + 8; + cache->saved_regs[I386_EIP_REGNUM] = cache->base + 4; + + cache->base_p = 1; + return cache; +} + +static void +i386_plt_stub_frame_this_id (struct frame_info *this_frame, void **this_cache, + struct frame_id *this_id) +{ + struct i386_frame_cache *cache = + i386_plt_stub_frame_cache (this_frame, this_cache); + + /* See the end of i386_push_dummy_call. */ + (*this_id) = frame_id_build (cache->base + 8, cache->pc); +} + +static struct value * +i386_plt_stub_frame_prev_register (struct frame_info *this_frame, + void **this_cache, int regnum) +{ + /* Make sure we've initialized the cache. */ + i386_plt_stub_frame_cache (this_frame, this_cache); + + return i386_frame_prev_register (this_frame, this_cache, regnum); +} + +static int +i386_plt_stub_frame_sniffer (const struct frame_unwind *self, + struct frame_info *this_frame, void **this_cache) +{ + CORE_ADDR pc = get_frame_pc (this_frame); + + if (!in_plt_section(pc, NULL)) + return 0; + + if (!i386_match_insn_block (pc, i386_plt_stub_insns) + && !i386_match_insn_block (pc, i386_plt0_stub_insns) + && !i386_match_insn_block (pc, i386_pic_plt_stub_insns) + && !i386_match_insn_block (pc, i386_pic_plt0_stub_insns)) + return 0; + + return 1; +} + +static const struct frame_unwind i386_plt_stub_frame_unwind = +{ + NORMAL_FRAME, + default_frame_unwind_stop_reason, + i386_plt_stub_frame_this_id, + i386_plt_stub_frame_prev_register, + NULL, + i386_plt_stub_frame_sniffer +}; + + /* Signal trampolines. */ static struct i386_frame_cache * @@ -3305,6 +3499,8 @@ i386_elf_init_abi (struct gdbarch_info i { /* We typically use stabs-in-ELF with the SVR4 register numbering. */ set_gdbarch_stab_reg_to_regnum (gdbarch, i386_svr4_reg_to_regnum); + + frame_unwind_append_unwinder (gdbarch, &i386_plt_stub_frame_unwind); } /* System V Release 4 (SVR4). */