From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-2.mimecast.com ([207.211.31.81]:53547 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726017AbgFARix (ORCPT ); Mon, 1 Jun 2020 13:38:53 -0400 Date: Mon, 1 Jun 2020 12:38:40 -0500 From: Josh Poimboeuf Subject: Re: [PATCH 0/2] Build ORC fast lookup table in scripts/sorttable tool Message-ID: <20200601173840.3f36m6l4fsu5bill@treble> References: <20200429064626.16389-1-changhuaixin@linux.alibaba.com> <20200522182815.ezanmvbemhzq2fmm@treble> <482837A8-E9D9-4229-B7B1-8E14403FB2AC@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <482837A8-E9D9-4229-B7B1-8E14403FB2AC@linux.alibaba.com> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: changhuaixin Cc: linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, bp@alien8.de, hpa@zytor.com, luto@amacapital.net, michal.lkml@markovi.net, mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, x86@kernel.org, yamada.masahiro@socionext.com On Sun, May 31, 2020 at 01:26:54PM +0800, changhuaixin wrote: > It turned out to be an alignment problem. If sh_size of previous section > orc_unwind is not 4-byte aligned, sh_offset of the following orc_lookup > section is not 4-byte aligned too. However, the VMA of section orc_lookup > is aligned to the nearest 4-byte. Thus, the orc_lookup section means two > different ares for scripts/sorttable tool and kernel. > > Sections headers look like this when it happens: > > 12 .orc_unwind_ip 00172124  ffffffff82573b28  0000000002573b28  01773b28 >  2**0 >                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA > 13 .orc_unwind   0022b1b6  ffffffff826e5c4c  00000000026e5c4c  018e5c4c >  2**0 >                  CONTENTS, ALLOC, LOAD, READONLY, DATA > 14 .orc_lookup   0003003c  ffffffff82910e04  0000000002910e04  01b10e02 >  2**0 >                  ALLOC > 15 .vvar         00001000  ffffffff82941000  0000000002941000  01b41000 >  2**4 >                  CONTENTS, ALLOC, LOAD, DATA > > Sorttable tool uses the are starting with offset 0x01b10e02 for 0x0003003c > bytes. While kernel use the area starting with VMA at  0xffffffff82910e04 > for 0x0003003c bytes, meaning that each entry in this table used by kernel > is actually 2 bytes behind the corresponding entry set from sorttable > tool. > > Any suggestion on fixing this？ The VMA and LMA are both 4-byte aligned. The file offset alignment (0x01b10e02) shouldn't matter. Actually it looks like the problem is that the section doesn't have CONTENTS, so it's just loaded as a BSS section (all zeros). The section needs to be type SHT_PROGBITS instead of SHT_NOBITS. $ readelf -S vmlinux |grep orc_lookup [16] .orc_lookup NOBITS ffffffff82b68418 01d68418 I tried to fix it with diff --git a/scripts/sorttable.h b/scripts/sorttable.h index a36c76c17be4..76adb1fb88f8 100644 --- a/scripts/sorttable.h +++ b/scripts/sorttable.h @@ -341,6 +341,7 @@ static int do_sort(Elf_Ehdr *ehdr, param.lookup_table_size = s->sh_size; param.orc_lookup_table = (unsigned int *) ((void *)ehdr + s->sh_offset); + w(SHT_PROGBITS, &s->sh_type); } if (!strcmp(secstrings + idx, ".text")) { param.text_size = s->sh_size; But that makes kallsyms unhappy, so I guess we need to do it from the linker script where .orc_lookup is created. Linker script doesn't seem to allow manual specification of the section type, so this is the best I could come up with: diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index db600ef218d7..49f4f5bc6165 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -826,6 +826,8 @@ . += (((SIZEOF(.text) + LOOKUP_BLOCK_SIZE - 1) / \ LOOKUP_BLOCK_SIZE) + 1) * 4; \ orc_lookup_end = .; \ + /* HACK: force SHT_PROGBITS so sorttable can edit: */ \ + BYTE(1); \ } #else #define ORC_UNWIND_TABLE