https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84790
Bug ID: 84790
Summary: Miscompilation for MIPS16 with -fpic and -Os or -O2
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mschif...@universe-factory.net
Target Milestone: ---
Created attachment 43609
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43609&action=edit
Reproducer C code
Compiling the following piece of C code:
void ext(void);
struct A {
unsigned v;
};
__attribute__((noinline))
void foo(void) {
ext();
}
__attribute__((noinline))
static void bar(struct A *a) {
if (a)
a->v--;
}
__attribute__((noinline))
static void baz(struct A *a) {
bar(a);
}
void test(struct A *a) {
baz(a);
foo();
baz(a);
}
using the command
mips-openwrt-linux-musl-gcc -Os -mips32r2 -mtune=24kc -mips16 -fpic -Wall
-Wextra -c -o reproducer.o reproducer.c
(current OpenWrt toolchain) generates the following code:
00000000 <bar>:
0: 2403 beqz a0,8 <bar+0x8>
2: 9c40 lw v0,0(a0)
4: 4aff addiu v0,-1
6: dc40 sw v0,0(a0)
8: e8a0 jrc ra
a: 6500 nop
0000000c <baz>:
c: f000 6a00 li v0,0
c: R_MIPS16_HI16 _gp_disp
10: f000 0b00 la v1,10 <baz+0x4>
10: R_MIPS16_LO16 _gp_disp
14: f400 3240 sll v0,16
18: e269 addu v0,v1
1a: 64c4 save 32,ra
1c: 659a move gp,v0
1e: d204 sw v0,16(sp)
20: 675c move v0,gp
22: f000 9a40 lw v0,0(v0)
22: R_MIPS16_GOT16 bar
26: f000 4a00 addiu v0,0
26: R_MIPS16_LO16 bar
2a: ea40 jalr v0
2c: 653a move t9,v0
2e: 6444 restore 32,ra
30: e8a0 jrc ra
32: 6500 nop
00000034 <foo>:
34: f000 6a00 li v0,0
34: R_MIPS16_HI16 _gp_disp
38: f000 0b00 la v1,38 <foo+0x4>
38: R_MIPS16_LO16 _gp_disp
3c: f400 3240 sll v0,16
40: e269 addu v0,v1
42: 64c4 save 32,ra
44: 659a move gp,v0
46: d204 sw v0,16(sp)
48: 675c move v0,gp
4a: f000 9a40 lw v0,0(v0)
4a: R_MIPS16_CALL16 ext
4e: ea40 jalr v0
50: 653a move t9,v0
52: 6444 restore 32,ra
54: e8a0 jrc ra
56: 6500 nop
00000058 <test>:
58: f000 6a00 li v0,0
58: R_MIPS16_HI16 _gp_disp
5c: f000 0b00 la v1,5c <test+0x4>
5c: R_MIPS16_LO16 _gp_disp
60: f400 3240 sll v0,16
64: e269 addu v0,v1
66: 659a move gp,v0
68: 677c move v1,gp
6a: 64f5 save 40,ra,s0-s1
6c: f000 9b00 lw s0,0(v1)
6c: R_MIPS16_GOT16 baz
70: d204 sw v0,16(sp)
72: f000 4800 addiu s0,0
72: R_MIPS16_LO16 baz
76: 6538 move t9,s0
78: e840 jalr s0
7a: 6724 move s1,a0
7c: 9604 lw a2,16(sp)
7e: f000 9b60 lw v1,0(v1)
7e: R_MIPS16_CALL16 foo
82: 659e move gp,a2
84: eb40 jalr v1
86: 653b move t9,v1
88: 6791 move a0,s1
8a: e840 jalr s0
8c: 6538 move t9,s0
8e: 6475 restore 40,ra,s0-s1
90: e8a0 jrc ra
92: 6500 nop
94: 6500 nop
96: 6500 nop
98: 6500 nop
9a: 6500 nop
9c: 6500 nop
9e: 6500 nop
This is incorrect: The GOT lookup for foo at 7e assumes that v1 still contains
the gp value set at 68, even though it is not valid anymore after the baz call
at 78.
We noticed this issue as it started to affect real software with GCC 7, but for
this reproducer code, GCC 5.4 and 5.5 produce identical code, so it is not a
regression per se.
Version: mips-openwrt-linux-musl-gcc -v
Reading specs from
/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/lib/gcc/mips-openwrt-linux-musl/7.3.0/specs
COLLECT_GCC=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/bin/mips-openwrt-linux-musl-gcc
COLLECT_LTO_WRAPPER=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/libexec/gcc/mips-openwrt-linux-musl/7.3.0/lto-wrapper
Target: mips-openwrt-linux-musl
Configured with:
/home/neoraider/Devel/OpenWrt/openwrt/build_dir/toolchain-mips_24kc_gcc-7.3.0_musl/gcc-7.3.0/configure
--with-bugurl=http://www.lede-project.org/bugs/ --with-pkgversion='OpenWrt GCC
7.3.0 r6401-edab12ec79aa'
--prefix=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=mips-openwrt-linux-musl --with-gnu-ld --enable-target-optspace
--disable-libgomp --disable-libmudflap --disable-multilib --disable-libmpx
--disable-nls --without-isl --without-cloog --with-host-libstdcxx=-lstdc++
--with-float=soft
--with-gmp=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/host
--with-mpfr=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/host
--with-mpc=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/host
--disable-decimal-float --with-mips-plt --with-diagnostics-color=auto-if-env
--disable-libssp --enable-__cxa_atexit
--with-headers=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/include
--disable-libsanitizer --enable-languages=c,c++ --enable-shared
--enable-threads
--with-slibdir=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/lib
--enable-lto
--with-libelf=/home/neoraider/Devel/OpenWrt/openwrt/staging_dir/host
Thread model: posix
gcc version 7.3.0 (OpenWrt GCC 7.3.0 r6401-edab12ec79aa)
