From patchwork Wed Mar 22 21:17:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Burgess X-Patchwork-Id: 66773 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id C0F5A385F014 for ; Wed, 22 Mar 2023 21:18:12 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C0F5A385F014 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1679519892; bh=fGGIQu2gSfCMm7ghPG4KSQrXbRkEXvzTVvCjmyRWMgY=; h=To:Cc:Subject:Date:In-Reply-To:References:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From:Reply-To:From; b=Vhib2xikUjVxne8cUIW85qciFEQ3eD2143tP3o598uNm8XG2aKStCHdo6TCZWSIZ3 idV5bM2OvypCpynKh4QL8ZUWJgzH844RGwgMAOs1xgmqLPGfJjGnBk8GIc4FjXMnvb rQP28eViqIgPj485JwHsPaXNW3xg3UxdQy2y20Ac= X-Original-To: gdb-patches@sourceware.org Delivered-To: gdb-patches@sourceware.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 0AA75385843D for ; Wed, 22 Mar 2023 21:17:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 0AA75385843D Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-260-xNLLo0a2Nzaq_RpTMH93rg-1; Wed, 22 Mar 2023 17:17:44 -0400 X-MC-Unique: xNLLo0a2Nzaq_RpTMH93rg-1 Received: by mail-wm1-f70.google.com with SMTP id iv10-20020a05600c548a00b003ee112e6df1so4110100wmb.2 for ; Wed, 22 Mar 2023 14:17:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679519863; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=fGGIQu2gSfCMm7ghPG4KSQrXbRkEXvzTVvCjmyRWMgY=; b=KU7ypsMnQLQqX8anWt7sRwlmn+vQQwGkIbW74xn84yhLvj5Odvdc6/rGqXJVRpYbeL l5J/JneGn36abxrn02Hy87iNOf59glNuQhKyXNAx5SAiZPV+fZO+N6jR51bY/L/b+VQz wlDPzYSKZ1YKN8Ho9RoCklO6afRDjN+6ULiFJBWkLlZ/mQfBCUKlc3IqSM+59SnbghyR 0cw5YZUcDLiACMnsdxfKmXn/zsQxF09HdeqZaYPohQ+gK+F3PbVHDY2Rw2YxfgxrDh4o iFScFZ1rHsvHMHNv+DJ6uWPGVGm+KiFlTWwkalkEXELqSPcY8x84IVFZoqR5YoZT4j+g +1RQ== X-Gm-Message-State: AAQBX9c1RvX9SpnZ5WObPDVqE8ENtgmkHsj+6ZU4aJCY3hr+3nAMObSl WAQRV41dDdUj8IY9qBYMCSxSt0O3oxv3TiGhGgzNngpjB0UV48eH3EtwlX9Nc5SDxAn7pf1VcbU F7EgHzMs1z3YfRCVQzVcEuls983unlNyJbH9AZ1wfTJ36/peBSur059Wd9p4c5znOEA/OgKc5cn 1+e0lZ7A== X-Received: by 2002:adf:f5c2:0:b0:2cf:f467:54d9 with SMTP id k2-20020adff5c2000000b002cff46754d9mr881949wrp.53.1679519862883; Wed, 22 Mar 2023 14:17:42 -0700 (PDT) X-Google-Smtp-Source: AKy350bUm4xvIThD3aZidrKCB81t+H6tg5nvhCC4zwyh8NN8VpT4rUnS4JzKh366JmQGhKsCL2gskg== X-Received: by 2002:adf:f5c2:0:b0:2cf:f467:54d9 with SMTP id k2-20020adff5c2000000b002cff46754d9mr881933wrp.53.1679519862434; Wed, 22 Mar 2023 14:17:42 -0700 (PDT) Received: from localhost (95.72.115.87.dyn.plus.net. [87.115.72.95]) by smtp.gmail.com with ESMTPSA id y16-20020a056000109000b002c56013c07fsm14540721wrw.109.2023.03.22.14.17.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 14:17:42 -0700 (PDT) To: gdb-patches@sourceware.org Cc: Pedro Alves , Simon Marchi , Andrew Burgess Subject: [PATCHv2 1/2] gdb: more debug output for displaced stepping Date: Wed, 22 Mar 2023 21:17:37 +0000 Message-Id: X-Mailer: git-send-email 2.25.4 In-Reply-To: References: <8473de37-fa6b-f7ec-e4b6-78b971324804@simark.ca> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-11.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Andrew Burgess via Gdb-patches From: Andrew Burgess Reply-To: Andrew Burgess Errors-To: gdb-patches-bounces+patchwork=sourceware.org@sourceware.org Sender: "Gdb-patches" While investigating a displaced stepping issue I wanted an easy way to see what GDB thought the original instruction was, and what instruction GDB replaced that with when performing the displaced step. We do print out the address that is being stepped, so I can track down the original instruction, I just need to go find the information myself. And we do print out the bytes of the new instruction, so I can figure out what the replacement instruction was, but it's not really easy. Also, the code that prints the bytes of the replacement instruction only prints 4 bytes, which clearly isn't always going to be correct. In this commit I remove the existing code that prints the bytes of the replacement instruction, and add two new blocks of code to displaced_step_prepare_throw. This new code prints the original instruction, and the replacement instruction. In each case we print both the bytes that make up the instruction and the completely disassembled instruction. Here's an example of what the output looks like on x86-64 (this is with 'set debug displaced on'). The two interesting lines contain the strings 'original insn' and 'replacement insn': (gdb) step [displaced] displaced_step_prepare_throw: displaced-stepping 2892655.2892655.0 now [displaced] displaced_step_prepare_throw: original insn 0x401030: ff 25 e2 2f 00 00 jmp *0x2fe2(%rip) # 0x404018 [displaced] prepare: selected buffer at 0x401052 [displaced] prepare: saved 0x401052: 1e fa 31 ed 49 89 d1 5e 48 89 e2 48 83 e4 f0 50 [displaced] fixup_riprel: %rip-relative addressing used. [displaced] fixup_riprel: using temp reg 2, old value 0x7ffff7f8a578, new value 0x401036 [displaced] amd64_displaced_step_copy_insn: copy 0x401030->0x401052: ff a1 e2 2f 00 00 68 00 00 00 00 e9 e0 ff ff ff [displaced] displaced_step_prepare_throw: prepared successfully thread=2892655.2892655.0, original_pc=0x401030, displaced_pc=0x401052 [displaced] displaced_step_prepare_throw: replacement insn 0x401052: ff a1 e2 2f 00 00 jmp *0x2fe2(%rcx) [displaced] finish: restored 2892655.2892655.0 0x401052 [displaced] amd64_displaced_step_fixup: fixup (0x401030, 0x401052), insn = 0xff 0xa1 ... [displaced] amd64_displaced_step_fixup: restoring reg 2 to 0x7ffff7f8a578 0x00007ffff7e402c0 in puts () from /lib64/libc.so.6 (gdb) One final note. For many targets that support displaced stepping (in fact all targets except ARM) the replacement instruction is always a single instruction. But on ARM the replacement could actually be a series of instructions. The debug code tries to handle this by disassembling the entire displaced stepping buffer. Obviously this might actually print more than is necessary, but there's (currently) no easy way to know how many instructions to disassemble; that knowledge is all locked in the architecture specific code. Still I don't think it really hurts, if someone is looking at this debug then hopefully they known what to expect. Obviously we can imagine schemes where the architecture specific displaced stepping code could communicate back how many bytes its replacement sequence was, and then our debug print code could use this to limit the disassembly. But this seems like a lot of effort just to save printing a few additional instructions in some debug output. I'm not proposing to do anything about this issue for now. --- gdb/infrun.c | 85 +++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 68 insertions(+), 17 deletions(-) diff --git a/gdb/infrun.c b/gdb/infrun.c index 5c9babb9104..8c56a9a4dfb 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -74,6 +74,7 @@ #include "gdbsupport/common-debug.h" #include "gdbsupport/buildargv.h" #include "extension.h" +#include "disasm.h" /* Prototypes for local functions */ @@ -1807,6 +1808,31 @@ displaced_step_prepare_throw (thread_info *tp) CORE_ADDR original_pc = regcache_read_pc (regcache); CORE_ADDR displaced_pc; + /* Display the instruction we are going to displaced step. */ + if (debug_displaced) + { + string_file tmp_stream; + int dislen = gdb_print_insn (gdbarch, original_pc, &tmp_stream, + nullptr); + + if (dislen > 0) + { + gdb::byte_vector insn_buf (dislen); + read_memory (original_pc, insn_buf.data (), insn_buf.size ()); + + std::string insn_bytes + = displaced_step_dump_bytes (insn_buf.data (), insn_buf.size ()); + + displaced_debug_printf ("original insn %s: %s \t %s", + paddress (gdbarch, original_pc), + insn_bytes.c_str (), + tmp_stream.string ().c_str ()); + } + else + displaced_debug_printf ("replacement insn %s: invalid length: %d", + paddress (gdbarch, original_pc), dislen); + } + displaced_step_prepare_status status = gdbarch_displaced_step_prepare (gdbarch, tp, displaced_pc); @@ -1845,6 +1871,48 @@ displaced_step_prepare_throw (thread_info *tp) paddress (gdbarch, original_pc), paddress (gdbarch, displaced_pc)); + /* Display the new displaced instruction(s). */ + if (debug_displaced) + { + string_file tmp_stream; + CORE_ADDR addr = displaced_pc; + + /* If displaced stepping is going to use h/w single step then we know + that the replacement instruction can only be a single instruction, + in that case set the end address at the next byte. + + Otherwise the displaced stepping copy instruction routine could + have generated multiple instructions, and all we know is that they + must fit within the LEN bytes of the buffer. */ + CORE_ADDR end + = addr + (gdbarch_displaced_step_hw_singlestep (gdbarch) + ? 1 : gdbarch_displaced_step_buffer_length (gdbarch)); + + while (addr < end) + { + int dislen = gdb_print_insn (gdbarch, addr, &tmp_stream, nullptr); + if (dislen <= 0) + { + displaced_debug_printf + ("replacement insn %s: invalid length: %d", + paddress (gdbarch, addr), dislen); + break; + } + + gdb::byte_vector insn_buf (dislen); + read_memory (addr, insn_buf.data (), insn_buf.size ()); + + std::string insn_bytes + = displaced_step_dump_bytes (insn_buf.data (), insn_buf.size ()); + std::string insn_str = tmp_stream.release (); + displaced_debug_printf ("replacement insn %s: %s \t %s", + paddress (gdbarch, addr), + insn_bytes.c_str (), + insn_str.c_str ()); + addr += dislen; + } + } + return DISPLACED_STEP_PREPARE_STATUS_OK; } @@ -2711,23 +2779,6 @@ resume_1 (enum gdb_signal sig) step = false; } - if (debug_displaced - && tp->control.trap_expected - && use_displaced_stepping (tp) - && !step_over_info_valid_p ()) - { - struct regcache *resume_regcache = get_thread_regcache (tp); - struct gdbarch *resume_gdbarch = resume_regcache->arch (); - CORE_ADDR actual_pc = regcache_read_pc (resume_regcache); - gdb_byte buf[4]; - - read_memory (actual_pc, buf, sizeof (buf)); - displaced_debug_printf ("run %s: %s", - paddress (resume_gdbarch, actual_pc), - displaced_step_dump_bytes - (buf, sizeof (buf)).c_str ()); - } - if (tp->control.may_range_step) { /* If we're resuming a thread with the PC out of the step