From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-x136.google.com (mail-lf1-x136.google.com [IPv6:2a00:1450:4864:20::136]) by sourceware.org (Postfix) with ESMTPS id 11DF83857828 for ; Wed, 3 Mar 2021 19:25:34 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 11DF83857828 Received: by mail-lf1-x136.google.com with SMTP id u4so38982012lfs.0 for ; Wed, 03 Mar 2021 11:25:34 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=bbl3O59Mr7XmlbWW937VBS6tgoGWRgMIqU/htK7AQlw=; b=N0i4VAMszkUeLt+4XVBfHgiU8NCdCW2rdGzFupguVKmzP+Pqv3Y6ZuHL/vAMLJDvZD X0m0pxK+8Mj/cJDIt15qmC1vWRxJIRe9ZVzVR4Sow6hIU7Z1oLNgMEq8I46IbonwltMc XjDbjOhn9/llzIMIBVv1vM6BwEGcFDdPi1QTwtS6mo52+V3/mbUWctB1SsjM64qOUA4z Q2P/BLr8iy14TZgsMMX9xpGDJ+xCW/9171r73zcU+GwlUhlYFkyWFU1b403KT8znwYeo c3PMSFDJnQ+FDtn57llBZRal5ovZ1u13u8d0iod8HJvjW+npxfpIcLr6jLKhY85r2/RD itxg== X-Gm-Message-State: AOAM5329OCPfMQ51gbJ1TBNIevVrt8zR35uyBR22YygbUxrZTyC+qLcV Lt48GLmvY4Ihsv/pE+9CRSOI+r3tjjjV6LyUs4GVendE X-Google-Smtp-Source: ABdhPJy6paWE0q+4/V3FA+lmLBHwnqdldQQxebcclpSSTw+rvT9CAoVrRweaRFLYU9XG2Shyl9WEUxnOy+9R6PZ7umo= X-Received: by 2002:a05:6512:3692:: with SMTP id d18mr159675lfs.128.1614799532110; Wed, 03 Mar 2021 11:25:32 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Evan Bowman Date: Wed, 3 Mar 2021 14:25:07 -0500 Message-ID: Subject: Re: Question about selectors in the Objective-C ABI To: gcc-help@gcc.gnu.org X-Spam-Status: No, score=-1.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, HTML_MESSAGE, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, 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 Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: gcc-help@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-help mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Mar 2021 19:25:38 -0000 Oh, perhaps not, maybe I'm still confused. On Wed, Mar 3, 2021 at 2:19 PM Evan Bowman wrote: > Never mind! I answered my own question. It seems that for short names, gcc > is doing a small size optimization, by storing string literals in-place > within the selectors, rather than as a pointer to the string. > > On Wed, Mar 3, 2021 at 12:05 PM Evan Bowman > wrote: > >> Hello, >> >> Yesterday, I was playing around with objective-c and GCC, and I have a >> question about module loading and selectors. >> >> Given this minimal sample code: >> ``` >> #import "Object.h" >> #include >> >> @interface HelloWorld:Object { >> } >> +(void) hello: (const char*) param; >> +(void) world: (const char*) param; >> @end >> >> @implementation HelloWorld >> +(void) hello: (const char*) param { >> printf("hello %s\n", param); >> } >> >> +(void) world: (const char*) param { >> printf("world %s\n", param); >> } >> @end >> >> int main() >> { >> [HelloWorld hello:"some text"]; >> } >> ``` >> >> I am able to get the code to compile and link with my own implementations >> of the objective-c runtime ABI functions, but I'm confused about how to >> determine the string name of a selector attached to a method definition. >> For example, I have this C code, which I run upon sending the hello: >> message to class HelloWorld, in the above example: >> >> void debug_walk_class(struct objc_class_gsv1* class, int depth) >> { >> printf("name: %s, info: %zu, inst_size: %zu, abi: %zu\n", >> class->name, >> class->info, >> class->instance_size, >> class->abi_version); >> >> if (class->methods) { >> struct objc_method_list_gcc* methods = class->methods; >> >> for (int i = 0; i < methods->count; ++i) { >> struct objc_method_gcc* method = &methods->methods[i]; >> printf("method: %s %zu\n", >> method->types ? method->types : "no types", >> method->selector->index); >> } >> } >> >> puts(""); >> >> if (class->isa && depth < 2) { >> debug_walk_class((struct objc_class_gsv1*)class->isa, depth + 1); >> } >> } >> >> id objc_msg_lookup(id receiver, SEL selector) >> { >> debug_walk_class((struct objc_class_gsv1*)receiver, 0); >> } >> >> The output, when walking the class tree, looks like this: >> name: (null), info: 0, inst_size: 94483748880412, abi: 1 >> >> name: HelloWorld, info: 1, inst_size: 8, abi: 0 >> >> name: HelloWorld, info: 2, inst_size: 104, abi: 0 >> method: v24@0:8r*16 5692614131986886519 >> method: v24@0:8r*16 8574917940748248424 >> >> So, I see the two methods in the metaclass, but when I try to print the >> selector->name string rather than selector->index, the code segfaults, so I >> guess the selector in this case holds an index rather than a string? Does >> anyone know how to determine the string name of the selector attached to an >> objc_method_gcc struct? If not, what does the index represent? The selector >> passed to objc_msg_lookup, on the other hand, does seem to be a string, I >> can print it just fine. >> >