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From: Tulio Magno Quites Machado Filho <tuliom@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/ibm/2.30/master] i386: Use comdat instead of .gnu.linkonce for i386 setup pic register (BZ #20543) Date: Tue, 12 May 2020 18:43:08 +0000 (GMT) [thread overview] Message-ID: <20200512184308.36A9B386F02B@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1ce16683d9efa1cc611ed4632645e16742699d10 commit 1ce16683d9efa1cc611ed4632645e16742699d10 Author: Adhemerval Zanella <adhemerval.zanella@linaro.org> Date: Fri Feb 28 10:46:14 2020 -0300 i386: Use comdat instead of .gnu.linkonce for i386 setup pic register (BZ #20543) GCC has moved from using .gnu.linkonce for i386 setup pic register with minimum current version (as for binutils minimum binutils that support comdat). Trying to pinpoint when binutils has added comdat support for i686, it seems it was around 2004 [1]. I also checking with some ancient binutils older than 2.16 I see: test.o: In function `__x86.get_pc_thunk.bx': test.o(.text.__x86.get_pc_thunk.bx+0x0): multiple definition of `__x86.get_pc_thunk.bx' /usr/lib/gcc/x86_64-linux-gnu/5/../../../i386-linux-gnu/crti.o(.gnu.linkonce.t.__x86.get_pc_thunk.bx+0x0): first defined here Which seems that such version can not handle either comdat at all or a mix of linkonce and comdat. For binutils 2.16.1 I am getting a different issue trying to link a binary with and more recent ctri.o (unrecognized relocation (0x2b) in section `.init', which is R_386_GOT32X and old binutils won't generate it anyway). So I think that either unlikely someone will use an older binutils than the one used to glibc and even this scenario may fail with some issue as the R_386_GOT32X. Also, 2.16.1 is quite old and not really supported (glibc itself required 2.25). Checked on i686-linux-gnu. [1] https://gcc.gnu.org/ml/gcc/2004-05/msg00030.html (cherry picked from commit 35200fd3892f6caf867bf89bc8048e553906af28) Diff: --- NEWS | 1 + sysdeps/i386/sysdep.h | 5 +++-- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/NEWS b/NEWS index d966688a56..76cfbcaa16 100644 --- a/NEWS +++ b/NEWS @@ -24,6 +24,7 @@ CVE-2020-1752: A use-after-free vulnerability in the glob function when The following bugs are resolved with this release: + [20543] Please move from .gnu.linkonce to comdat [23518] login: Remove utmp backend jump tables [24682] localedata: zh_CN first weekday should be Monday per GB/T 7408-2005 diff --git a/sysdeps/i386/sysdep.h b/sysdeps/i386/sysdep.h index 749b55b077..eee6d586c1 100644 --- a/sysdeps/i386/sysdep.h +++ b/sysdeps/i386/sysdep.h @@ -61,7 +61,7 @@ lose: SYSCALL_PIC_SETUP \ # define SETUP_PIC_REG(reg) \ .ifndef GET_PC_THUNK(reg); \ - .section .gnu.linkonce.t.GET_PC_THUNK(reg),"ax",@progbits; \ + .section .text.GET_PC_THUNK(reg),"axG",@progbits,GET_PC_THUNK(reg),comdat; \ .globl GET_PC_THUNK(reg); \ .hidden GET_PC_THUNK(reg); \ .p2align 4; \ @@ -97,7 +97,8 @@ GET_PC_THUNK(reg): \ # define SETUP_PIC_REG_STR(reg) \ ".ifndef " GET_PC_THUNK_STR (reg) "\n" \ - ".section .gnu.linkonce.t." GET_PC_THUNK_STR (reg) ",\"ax\",@progbits\n" \ + ".section .text." GET_PC_THUNK_STR (reg) ",\"axG\",@progbits," \ + GET_PC_THUNK_STR (reg) ",comdat\n" \ ".globl " GET_PC_THUNK_STR (reg) "\n" \ ".hidden " GET_PC_THUNK_STR (reg) "\n" \ ".p2align 4\n" \
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