From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by sourceware.org (Postfix) with ESMTP id A55973858C83 for ; Thu, 11 May 2023 11:35:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org A55973858C83 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [113.200.148.30]) by gateway (Coremail) with SMTP id _____8CxE_AN01xkGLwHAA--.13237S3; Thu, 11 May 2023 19:35:43 +0800 (CST) Received: from [10.130.0.149] (unknown [113.200.148.30]) by localhost.localdomain (Coremail) with SMTP id AQAAf8DxD78L01xksLpVAA--.21395S3; Thu, 11 May 2023 19:35:39 +0800 (CST) Subject: Re: [PATCH v2 RESEND] gdb/elfread.c: Add plt symbol check for _PROCEDURE_LINKAGE_TABLE_ To: Hui Li , gdb-patches@sourceware.org, Tom Tromey References: <20230410123030.25326-1-lihui@loongson.cn> From: Tiezhu Yang Message-ID: <57010698-8358-ba0d-3e20-b58f72202d66@loongson.cn> Date: Thu, 11 May 2023 19:35:39 +0800 User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20230410123030.25326-1-lihui@loongson.cn> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID:AQAAf8DxD78L01xksLpVAA--.21395S3 X-CM-SenderInfo: p1dqw3xlh2x3gn0dqz5rrqw2lrqou0/ X-Coremail-Antispam: 1Uk129KBjvJXoW3WFykGw4kGF47Jw47Zr1fWFg_yoW7Ar13pr WUtFW5GFs5X348Awn7Jr1rXF4rZrn3AF1UArW5Kr1avrW5WFn7XrW8G3y5KayrJrs0yFyI v3ZrZr40yrn5AaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUj1kv1TuYvTs0mT0YCTnIWj qI5I8CrVACY4xI64kE6c02F40Ex7xfYxn0WfASr-VFAUDa7-sFnT9fnUUIcSsGvfJTRUUU bI8YFVCjjxCrM7AC8VAFwI0_Jr0_Gr1l1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s 1l1IIY67AEw4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xv wVC0I7IYx2IY67AKxVWUJVWUCwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVWUJVW8JwA2z4 x0Y4vEx4A2jsIE14v26r4UJVWxJr1l84ACjcxK6I8E87Iv6xkF7I0E14v26F4UJVW0owAS 0I0E0xvYzxvE52x082IY62kv0487Mc804VCY07AIYIkI8VC2zVCFFI0UMc02F40EFcxC0V AKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Gr0_Cr1l Ox8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxk0xIA0c2IEe2xFo4CEbIxvr21l42 xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWU GwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1Y6r17MIIYrxkI7VAKI4 8JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4U MIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVW8JVWxJwCI42IY6I 8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxU20PSUUUUU X-Spam-Status: No, score=-12.3 required=5.0 tests=BAYES_00,GIT_PATCH_0,KAM_DMARC_STATUS,KAM_STOCKGEN,NICE_REPLY_A,SPF_HELO_PASS,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 04/10/2023 08:30 PM, Hui Li wrote: > In the current code, when execute the following test on LoongArch: > > $ make check-gdb TESTS="gdb.base/gnu-ifunc.exp" > === gdb Summary === > > # of expected passes 111 > # of unexpected failures 62 > > According to IFUNC's working process [1]. first time the IFUNC function > is called, the dynamic linker will not simply fill the .got.plt entry > with the actual address of IFUNC symbol, it will call the IFUNC resolver > function and take the return address, uses it as the sym-bound address > and puts it in the .got.plt entry. Initial address in .got.plt entry is > not a real function addresss. Depending on the compiler implementation, > some different addresses will be filled in. Most architectures will use > a .plt entry address to fill in the corresponding .got.plt entry. > > In gdb, elf_gnu_ifunc_resolve_addr() will be called to return a real > IFUNC function addresss. First check to see if the real address for > the IFUNC symbol has been resolved by the following function: > > elf_gnu_ifunc_resolve_name (const char *name, CORE_ADDR *addr_p) > { > if (elf_gnu_ifunc_resolve_by_cache (name, addr_p)) > return true; > > if (elf_gnu_ifunc_resolve_by_got (name, addr_p)) > return true; > > return false; > } > > in elf_gnu_ifunc_resolve_by_got(), it gets the contents of the > .got.plt entry and determines if the contents is the correct address > by calling elf_gnu_ifunc_record_cache(). Based on the IFUNC working > principle analysis above, the address filled in the .got.plt entry is > not the actual target function address initially, it would be a .plt > entry address corresponding symbol like *@plt. In this case, gdb just > go back to execute the resolver function and puts the return address > in the .got.plt entry. After that, gdb can get a real ifun address via > .got.plt entry. > > On LoongArch, initially, each address filled in the .got.plt entries > is the first .plt entry address. Some architectures such as LoongArch > define the symbol _PROCEDURE_LINKAGE_TABLE_ at the start of the .plt > section. This symbol is the first plt entry, so gdb needs to check > this symbol in elf_gnu_ifunc_record_cache(). > > On LoongArch .got.plt and .plt section as follow: > > $objdump -D gdb/testsuite/outputs/gdb.base/gnu-ifunc/gnu-ifunc-0-0-0 > ... > 0000000120010008 <.got.plt>: > 120010008: ffffffff 0xffffffff > 12001000c: ffffffff 0xffffffff > ... > 120010018: 20004000 ll.w $zero, $zero, 64(0x40) > 12001001c: 00000001 0x00000001 > 120010020: 20004000 ll.w $zero, $zero, 64(0x40) > 120010024: 00000001 0x00000001 > 120010028: 20004000 ll.w $zero, $zero, 64(0x40) > 12001002c: 00000001 0x00000001 > 120010030: 20004000 ll.w $zero, $zero, 64(0x40) > 120010034: 00000001 0x00000001 > > ... > Disassembly of section .plt: > > 0000000120004000 <_PROCEDURE_LINKAGE_TABLE_>: > 120004000: 1c00018e pcaddu12i $t2, 12(0xc) > 120004004: 0011bdad sub.d $t1, $t1, $t3 > 120004008: 28c021cf ld.d $t3, $t2, 8(0x8) > 12000400c: 02ff51ad addi.d $t1, $t1, -44(0xfd4) > 120004010: 02c021cc addi.d $t0, $t2, 8(0x8) > 120004014: 004505ad srli.d $t1, $t1, 0x1 > 120004018: 28c0218c ld.d $t0, $t0, 8(0x8) > 12000401c: 4c0001e0 jirl $zero, $t3, 0 > > 0000000120004020 <__libc_start_main@plt>: > 120004020: 1c00018f pcaddu12i $t3, 12(0xc) > 120004024: 28ffe1ef ld.d $t3, $t3, -8(0xff8) > 120004028: 4c0001ed jirl $t1, $t3, 0 > 12000402c: 03400000 andi $zero, $zero, 0x0 > > 0000000120004030 : > 120004030: 1c00018f pcaddu12i $t3, 12(0xc) > 120004034: 28ffc1ef ld.d $t3, $t3, -16(0xff0) > 120004038: 4c0001ed jirl $t1, $t3, 0 > 12000403c: 03400000 andi $zero, $zero, 0x0 > > 0000000120004040 : > 120004040: 1c00018f pcaddu12i $t3, 12(0xc) > 120004044: 28ffa1ef ld.d $t3, $t3, -24(0xfe8) > 120004048: 4c0001ed jirl $t1, $t3, 0 > 12000404c: 03400000 andi $zero, $zero, 0x0 > ... > > With this patch: > > $make check-gdb TESTS="gdb.base/gnu-ifunc.exp" > === gdb Summary === > > #of expected passes 173 > > [1] https://sourceware.org/glibc/wiki/GNU_IFUNC > > Signed-off-by: Hui Li > --- > gdb/elfread.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/gdb/elfread.c b/gdb/elfread.c > index b414da9ed21..1e606783c33 100644 > --- a/gdb/elfread.c > +++ b/gdb/elfread.c > @@ -722,6 +722,9 @@ elf_gnu_ifunc_record_cache (const char *name, CORE_ADDR addr) > if (len > 4 && strcmp (target_name + len - 4, "@plt") == 0) > return 0; > > + if (strcmp (target_name, "_PROCEDURE_LINKAGE_TABLE_") == 0) > + return 0; > + > htab = elf_objfile_gnu_ifunc_cache_data.get (objfile); > if (htab == NULL) > { > Hi, I noticed the following review comments by Tom Tromey [1] on Mar 24: It would be helpful to know how precisely things go wrong. The patch itself seems reasonable enough -- hacky maybe but not out of the ordinary way -- but I don't understand how it relates to the problem. Like, why does ignoring this symbol here affect the results? Are you OK for this v2 patch with the updated commit message resent on Apr 10 [2]? If no more comments, let me push this patch next week. [1] https://sourceware.org/pipermail/gdb-patches/2023-March/198285.html [2] https://sourceware.org/pipermail/gdb-patches/2023-April/198731.html Thanks, Tiezhu