From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by sourceware.org (Postfix) with ESMTPS id 0138D3858012 for ; Tue, 30 Mar 2021 21:33:11 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 0138D3858012 Received: from simark.ca (simark.ca [158.69.221.121]) (authenticated bits=0) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 12ULX54P006803 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 30 Mar 2021 17:33:10 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 12ULX54P006803 Received: from [10.0.0.11] (192-222-157-6.qc.cable.ebox.net [192.222.157.6]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id 4A0491E789; Tue, 30 Mar 2021 17:33:05 -0400 (EDT) Subject: Re: Remote query for structure layout To: Tim Newsome , gdb References: From: Simon Marchi Message-ID: Date: Tue, 30 Mar 2021 17:33:04 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Tue, 30 Mar 2021 21:33:05 +0000 X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_PASS, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gdb@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 30 Mar 2021 21:33:13 -0000 On 2021-03-30 4:35 p.m., Tim Newsome wrote: > On Sun, Mar 28, 2021 at 5:00 AM wrote: > >> I would like to propose a new command for the remote protocol that can be >> used to >> query structure layouts. >> Essentially a `qSymbol` equivalent for the output of `ptype`. >> > > I'm really interested in this. I've been working on OpenOCD FreeRTOS > support and as Thomas points out, it's a fragile mess. > > There's another use case that this would be great for. FreeRTOS stores > registers on the stack when it switches to another thread. OpenOCD needs to > know what this register layout is, and it also depends on compile time > options. With this mechanism I think it would be possible for FreeRTOS to > define a struct that represents how the registers are laid out on the > stack. E.g.: > struct register_stacking_t { > uint32_t x1; > uint32_t x2; > uint32_t x3; > uint32_t x4; > ... > uint32_t pc; > }; > > Am I right that this will end up in the dwarf info even if the struct > itself isn't used anywhere in the FreeRTOS code? This would simplify so > much. It doesn't seem like it: $ cat test.cpp struct foo { int a; }; int main() { } $ g++ test.cpp -g3 -O0 $ llvm-dwarfdump -F -color a.out a.out: file format elf64-x86-64 .debug_info contents: 0x00000000: Compile Unit: length = 0x00000053, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000057) 0x0000000b: DW_TAG_compile_unit DW_AT_producer [DW_FORM_strp] ("GNU C++14 10.2.0 -mtune=generic -march=x86-64 -g3 -O0") DW_AT_language [DW_FORM_data1] (DW_LANG_C_plus_plus) DW_AT_name [DW_FORM_strp] ("test.cpp") DW_AT_comp_dir [DW_FORM_strp] ("/home/simark/build/lttng-ust/doc/examples/easy-ust") DW_AT_low_pc [DW_FORM_addr] (0x0000000000001119) DW_AT_high_pc [DW_FORM_data8] (0x000000000000000b) DW_AT_stmt_list [DW_FORM_sec_offset] (0x00000000) DW_AT_GNU_macros [DW_FORM_sec_offset] (0x00000000) 0x00000031: DW_TAG_base_type DW_AT_byte_size [DW_FORM_data1] (0x04) DW_AT_encoding [DW_FORM_data1] (DW_ATE_signed) DW_AT_name [DW_FORM_string] ("int") 0x00000038: DW_TAG_subprogram DW_AT_external [DW_FORM_flag_present] (true) DW_AT_name [DW_FORM_strp] ("main") DW_AT_decl_file [DW_FORM_data1] ("/home/simark/build/lttng-ust/doc/examples/easy-ust/test.cpp") DW_AT_decl_line [DW_FORM_data1] (6) DW_AT_decl_column [DW_FORM_data1] (0x05) DW_AT_type [DW_FORM_ref4] (0x00000031 "int") DW_AT_low_pc [DW_FORM_addr] (0x0000000000001119) DW_AT_high_pc [DW_FORM_data8] (0x000000000000000b) DW_AT_frame_base [DW_FORM_exprloc] (DW_OP_call_frame_cfa) DW_AT_GNU_all_call_sites [DW_FORM_flag_present] (true) 0x00000056: NULL There might be some clever trick to force the compiler in emitting it though, but I suppose it will always be a bit fragile, dependent on the particular compiler. Simon