https://sourceware.org/bugzilla/show_bug.cgi?id=20852
Bug ID: 20852
Summary: glibc/MIPS strfry call strlen by bal not jalr
Product: binutils
Version: 2.26
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: ambrosehua at 126 dot com
Target Milestone: ---
Fedora 21/loongson glibc 2.20 n64，function strfry.c is compiled with calling
strlen with jalr in strfry.os, but in
final libc-2.20.so, the function strfry is built with calling strlen with bal.
I think it has something to do with gcc's
-mrelax-pic-calls option.
++++++++++++++++++++++++++
strfry in libc.so
......
00000000000c0e00 <strfry>:
c0e00: 67bdffb0 daddiu sp,sp,-80
c0e04: ffbc0040 sd gp,64(sp)
c0e08: 3c1c0013 lui gp,0x13
c0e0c: 0399e02d daddu gp,gp,t9
c0e10: ffb10018 sd s1,24(sp)
c0e14: 679cea20 daddiu gp,gp,-5600
c0e18: ffb00010 sd s0,16(sp)
c0e1c: 0080802d move s0,a0
c0e20: df9180b0 ld s1,-32592(gp)
c0e24: ffbf0048 sd ra,72(sp)
c0e28: ffb50038 sd s5,56(sp)
c0e2c: 8e22b370 lw v0,-19600(s1)
c0e30: ffb40030 sd s4,48(sp)
c0e34: ffb30028 sd s3,40(sp)
c0e38: 1040002b beqz v0,c0ee8 <strfry+0xe8>
c0e3c: ffb20020 sd s2,32(sp)
c0e40: df9980d0 ld t9,-32560(gp) // t9
pointed to new strlen addr not the strlen in glibc when interposing
c0e44: 0411ef52 bal bcb90 <strlen> //here it
is, jalr is in strfry.os and libc_pic.os
c0e48: 0200202d move a0,s0
c0e4c: 0040882d move s1,v0
c0e50: 2c420002 sltiu v0,v0,2
c0e54: 14400018 bnez v0,c0eb8 <strfry+0xb8>
c0e58: df9280b0 ld s2,-32592(gp)
c0e5c: 6633ffff daddiu s3,s1,-1
c0e60: 0200a82d move s5,s0
c0e64: 0000a02d move s4,zero
c0e68: 6652b340 daddiu s2,s2,-19648
c0e6c: 00000000 nop
........
I also check the libc_pic.os, it has the same strfry as strfry.os, which is
used by ld in building final libc.so,
#. According to SVR4, global function strlen in glibc should be able to be
interposed, however, it is called by
bal not jalr, so is it a bug since the symbol interpositon for strlen in strfry
is unavailable?
#. Suppose the strlen in glibc is using gp. When strlen is being interposed,
the t9 is pointed to the new strlen, "bal strlen"
is calling strlen in glibc with wrong t9 and wrong gp. OOPS!
I also check Gentoo/MIPS glibc2.23 n32, O32/N64/gcc 4.8.5/binutils 2.24 p1.4,
same symptom as Fedora 21/loongson glibc-2.20
binutils 2.25 / gcc 4.9.3,
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