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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)
This commit is contained in:
Adhemerval Zanella 2020-02-28 10:46:14 -03:00
parent 6b11f60c70
commit 1ce16683d9
2 changed files with 4 additions and 2 deletions
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NEWS
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@ -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

5
sysdeps/i386/sysdep.h
View File

@ -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" \