From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELvWQEOm11tOFRcBwHP+I32QUHtSNXOD28RD/UXqiMy/KtIw2IUmc5WrOUGNvhCPL+0I/2Zw ARC-Seal: i=1; a=rsa-sha256; t=1521214129; cv=none; d=google.com; s=arc-20160816; b=RWeMzfxzt8H8x+qwhAgi7iHeLI6seEU/8b56nhHCG4ber4/eRfMluPq3kRGqmkYoLP PECRsXwbpRTz1YeNPEMoPEXdCYtczR4paBmOZyZEZFR2GdhFjicpYPWPRSW2HTCypvBL iW3xKfkbq00iB5pPgJOS7GDN7xt/VU2Je9JLrVVYh2eQ1c+5lp94HFzzFxrW8EZfhoMF Q7cv85sxrIQdCVIVEC4Agfm/hsYWh0Bxo60EtJJ7feHQ5rC0Q5bPsM04EabaEf8YXfZ7 aeae4Bgo8YM+e1aNu+IYBhs1jGVnDfOcV9rauvUx8rtDImL9zq0YOmqH3WyLn4XHVF4r D+2w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=cFtn8glGYSMV9R5x0kBIwy0NwyKSrAHKHfO3a+u0hf0=; b=vmT2xN5tNsrjMCCI5oOyHnEihq4H5S6NbMVcfW+lFSCT5s0uD2b8T9bRaz9woqEFa+ eRxHuO5090BlDf/W36wIje8sSyUaWKMtR2psnPUTt6uZoAppDdLmy/ASuNKicp6wlpO3 35ODMEB7oq0QRuHjIMKfAabbTDkA77+ps2gmJbdsR4llo7tFLjZiSo8Kjg2eoxfnkeja rADMZw86ouMf6gq/Pjt8yStmGZKhjgptRSLV/02khUYDs2fxt6IagA6a6cKq8hLFhhC0 MXSU0I/7ZSJ2YLa0U+6npE+ugr49oICV7jh7/rWE7WA2How5++PnKN3MpLPpJYMrvYuK 9eEw== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "H.J. Lu" , Linus Torvalds , Matthias Kaehlcke Subject: [PATCH 4.4 51/63] x86: Treat R_X86_64_PLT32 as R_X86_64_PC32 Date: Fri, 16 Mar 2018 16:23:23 +0100 Message-Id: <20180316152305.620032754@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180316152259.964532775@linuxfoundation.org> References: <20180316152259.964532775@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1595108490440452142?= X-GMAIL-MSGID: =?utf-8?q?1595108626813159466?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: H.J. Lu commit b21ebf2fb4cde1618915a97cc773e287ff49173e upstream. On i386, there are 2 types of PLTs, PIC and non-PIC. PIE and shared objects must use PIC PLT. To use PIC PLT, you need to load _GLOBAL_OFFSET_TABLE_ into EBX first. There is no need for that on x86-64 since x86-64 uses PC-relative PLT. On x86-64, for 32-bit PC-relative branches, we can generate PLT32 relocation, instead of PC32 relocation, which can also be used as a marker for 32-bit PC-relative branches. Linker can always reduce PLT32 relocation to PC32 if function is defined locally. Local functions should use PC32 relocation. As far as Linux kernel is concerned, R_X86_64_PLT32 can be treated the same as R_X86_64_PC32 since Linux kernel doesn't use PLT. R_X86_64_PLT32 for 32-bit PC-relative branches has been enabled in binutils master branch which will become binutils 2.31. [ hjl is working on having better documentation on this all, but a few more notes from him: "PLT32 relocation is used as marker for PC-relative branches. Because of EBX, it looks odd to generate PLT32 relocation on i386 when EBX doesn't have GOT. As for symbol resolution, PLT32 and PC32 relocations are almost interchangeable. But when linker sees PLT32 relocation against a protected symbol, it can resolved locally at link-time since it is used on a branch instruction. Linker can't do that for PC32 relocation" but for the kernel use, the two are basically the same, and this commit gets things building and working with the current binutils master - Linus ] Signed-off-by: H.J. Lu Signed-off-by: Linus Torvalds Cc: Matthias Kaehlcke Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/machine_kexec_64.c | 1 + arch/x86/kernel/module.c | 1 + arch/x86/tools/relocs.c | 3 +++ 3 files changed, 5 insertions(+) --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -519,6 +519,7 @@ int arch_kexec_apply_relocations_add(con goto overflow; break; case R_X86_64_PC32: + case R_X86_64_PLT32: value -= (u64)address; *(u32 *)location = value; break; --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -189,6 +189,7 @@ int apply_relocate_add(Elf64_Shdr *sechd goto overflow; break; case R_X86_64_PC32: + case R_X86_64_PLT32: if (*(u32 *)loc != 0) goto invalid_relocation; val -= (u64)loc; --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -769,9 +769,12 @@ static int do_reloc64(struct section *se break; case R_X86_64_PC32: + case R_X86_64_PLT32: /* * PC relative relocations don't need to be adjusted unless * referencing a percpu symbol. + * + * NB: R_X86_64_PLT32 can be treated as R_X86_64_PC32. */ if (is_percpu_sym(sym, symname)) add_reloc(&relocs32neg, offset);