进入rootfs后，执行top命令，一段时间后，仍然出现Illegal instruction。于是开启core dump：
# ulimit -c unlimited
# echo "/tmp/core-%e-%s-%u-%g-%p-%t" > /proc/sys/kernel/core_pattern
启动top按enter快速刷新很快出现了core。使用gdb进行调试
$ ~/toolchain/crosstool-ipq50xx_32/bin/arm-linux-gnueabi-gdb bin/busybox /work/core-top-4-0-0-86-8580
GNU gdb (crosstool-NG 1.25.0) 11.2
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=x86_64-build_pc-linux-gnu --target=arm-linux-gnueabi".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from bin/busybox...
(No debugging symbols found in bin/busybox)
warning: Can't open file /bin/busybox during file-backed mapping note processing
warning: core file may not match specified executable file.
[New LWP 86]
Core was generated by `top'.
Program terminated with signal SIGILL, Illegal instruction.
#0 __memchr_neon () at ../sysdeps/arm/armv7/multiarch/memchr_neon.S:92
92 ../sysdeps/arm/armv7/multiarch/memchr_neon.S: No such file or directory.
(gdb) bt
#0 __memchr_neon () at ../sysdeps/arm/armv7/multiarch/memchr_neon.S:92
#1 0x76d815f0 in __GI__IO_getline_info (fp=fp@entry=0x11e540, buf=buf@entry=0x7ea95b2c "M\375\021", n=<optimized out>, delim=delim@entry=10,
extract_delim=1, extract_delim@entry=1179776, eof=eof@entry=0x0) at iogetline.c:85
#2 0x76d81728 in __GI__IO_getline (fp=fp@entry=0x11e540, buf=buf@entry=0x7ea95b2c "M\375\021", n=<optimized out>, delim=delim@entry=10,
extract_delim=extract_delim@entry=1) at iogetline.c:34
#3 0x76d8b30c in __GI___fgets_unlocked (buf=0x7ea95b2c "M\375\021", n=<optimized out>, fp=0x11e540) at iofgets_u.c:52
#4 0x0006b144 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
看起来是glibc的浮点数设置的不对：
yuan@yuan-vm:~/toolchain/crosstool-ipq50xx_32$ bin/arm-linux-gnueabi-readelf -A arm-linux-gnueabi/sysroot/lib/libc.so.6
Attribute Section: aeabi
File Attributes
Tag_CPU_name: "7-A"
Tag_CPU_arch: v7
Tag_CPU_arch_profile: Application
Tag_ARM_ISA_use: Yes
Tag_THUMB_ISA_use: Thumb-2
Tag_FP_arch: VFPv3
Tag_Advanced_SIMD_arch: NEONv1
Tag_ABI_PCS_wchar_t: 4
Tag_ABI_FP_rounding: Needed
Tag_ABI_FP_denormal: Needed
Tag_ABI_FP_exceptions: Needed
Tag_ABI_FP_user_exceptions: Needed
Tag_ABI_FP_number_model: IEEE 754
Tag_ABI_align_needed: 8-byte
Tag_ABI_enum_size: int
Tag_ABI_optimization_goals: Aggressive Speed
Tag_CPU_unaligned_access: v6
根据参考文档2，查看gcc的支持的arch。
~/toolchain/crosstool-ipq50xx_32$ echo | bin/arm-linux-gnueabi-gcc -v -E -
Using built-in specs.
COLLECT_GCC=bin/arm-linux-gnueabi-gcc
Target: arm-linux-gnueabi
Configured with: /work/git/Xrouter/staging/ipq50xx_32/toolchain/building_dir/arm-linux-gnueabi/src/gcc/configure --build=x86_64-build_pc-linux-gnu
--host=x86_64-build_pc-linux-gnu --target=arm-linux-gnueabi --prefix=/home/yuan/toolchain/crosstool-ipq50xx_32 --exec_prefix=/home/yuan/toolchain
/crosstool-ipq50xx_32 --with-sysroot=/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot --enable-languages=c,c++ --with-arch=armv
7-a --with-float=soft --with-pkgversion='crosstool-NG 1.25.0' --enable-__cxa_atexit --disable-libmudflap --disable-libgomp --disable-libssp --disa
ble-libquadmath --disable-libquadmath-support --disable-libsanitizer --disable-libmpx --disable-libstdcxx-verbose --with-gmp=/work/git/Xrouter/sta
ging/ipq50xx_32/toolchain/building_dir/arm-linux-gnueabi/buildtools --with-mpfr=/work/git/Xrouter/staging/ipq50xx_32/toolchain/building_dir/arm-li
nux-gnueabi/buildtools --with-mpc=/work/git/Xrouter/staging/ipq50xx_32/toolchain/building_dir/arm-linux-gnueabi/buildtools --with-isl=/work/git/Xr
outer/staging/ipq50xx_32/toolchain/building_dir/arm-linux-gnueabi/buildtools --enable-lto --enable-threads=posix --enable-target-optspace --disabl
e-plugin --disable-nls --disable-multilib --with-local-prefix=/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot --enable-long-lo
ng
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.2.0 (crosstool-NG 1.25.0)
COLLECT_GCC_OPTIONS='-v' '-E' '-mfloat-abi=soft' '-mtls-dialect=gnu' '-marm' '-mlibarch=armv7-a' '-march=armv7-a'
/home/yuan/toolchain/crosstool-ipq50xx_32/libexec/gcc/arm-linux-gnueabi/11.2.0/cc1 -E -quiet -v - -mfloat-abi=soft -mtls-dialect=gnu -marm -mlibarch=armv7-a -march=armv7-a -dumpbase -
ignoring nonexistent directory "/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot/home/yuan/toolchain/crosstool-ipq50xx_32/arm-l
inux-gnueabi/sysroot/include"
#include "..." search starts here:
#include <...> search starts here:
/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-linux-gnueabi/11.2.0/include
/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-linux-gnueabi/11.2.0/include-fixed
/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-linux-gnueabi/11.2.0/../../../../arm-linux-gnueabi/include
/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot/usr/include
End of search list.
# 0 "<stdin>"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "<stdin>"
COMPILER_PATH=/home/yuan/toolchain/crosstool-ipq50xx_32/libexec/gcc/arm-linux-gnueabi/11.2.0/:/home/yuan/toolchain/crosstool-ipq50xx_32/libexec/gc
c/arm-linux-gnueabi/11.2.0/:/home/yuan/toolchain/crosstool-ipq50xx_32/libexec/gcc/arm-linux-gnueabi/:/home/yuan/toolchain/crosstool-ipq50xx_32/lib
/gcc/arm-linux-gnueabi/11.2.0/:/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-linux-gnueabi/:/home/yuan/toolchain/crosstool-ipq50xx_32/lib/
gcc/arm-linux-gnueabi/11.2.0/../../../../arm-linux-gnueabi/bin/
LIBRARY_PATH=/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-linux-gnueabi/11.2.0/:/home/yuan/toolchain/crosstool-ipq50xx_32/lib/gcc/arm-lin
ux-gnueabi/11.2.0/../../../../arm-linux-gnueabi/lib/:/home/yuan/toolchain/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot/lib/:/home/yuan/toolchain
/crosstool-ipq50xx_32/arm-linux-gnueabi/sysroot/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-E' '-mfloat-abi=soft' '-mtls-dialect=gnu' '-marm' '-mlibarch=armv7-a' '-march=armv7-a'
$ ~/toolchain/crosstool-ipq50xx_32$ bin/arm-linux-gnueabi-gcc -Q --help=target
The following options are target specific:
-mabi= aapcs-linux
-mabort-on-noreturn [disabled]
-mandroid [disabled]
-mapcs [disabled]
-mapcs-frame [disabled]
-mapcs-reentrant [disabled]
-mapcs-stack-check [disabled]
-march= armv7-a
-marm [enabled]
-masm-syntax-unified [disabled]
-mbe32 [enabled]
-mbe8 [disabled]
-mbig-endian [disabled]
-mbionic [disabled]
-mbranch-cost= -1
-mcallee-super-interworking [disabled]
-mcaller-super-interworking [disabled]
-mcmse [disabled]
-mcpu=
-mfdpic [disabled]
-mfix-cortex-m3-ldrd [disabled]
-mflip-thumb [disabled]
-mfloat-abi= soft
-mfp16-format= none
-mfpu= auto
-mgeneral-regs-only [disabled]
-mglibc [enabled]
-mhard-float -mfloat-abi=hard
-mlibarch= armv7-a
-mlittle-endian [enabled]
-mlong-calls [disabled]
-mmusl [disabled]
-mneon-for-64bits [disabled]
-mpic-data-is-text-relative [enabled]
-mpic-register=
-mpoke-function-name [disabled]
-mprint-tune-info [disabled]
-mpure-code [disabled]
-mrestrict-it [disabled]
-msched-prolog [enabled]
-msingle-pic-base [disabled]
-mslow-flash-data [disabled]
-msoft-float -mfloat-abi=soft
-mstructure-size-boundary= 8
-mthumb [disabled]
-mthumb-interwork [disabled]
-mtls-dialect= gnu
-mtp= cp15
-mtpcs-frame [disabled]
-mtpcs-leaf-frame [disabled]
-mtune=
-muclibc [disabled]
-munaligned-access [enabled]
-mvectorize-with-neon-double [disabled]
-mvectorize-with-neon-quad [enabled]
-mword-relocations [disabled]
Known ARM ABIs (for use with the -mabi= option):
aapcs aapcs-linux apcs-gnu atpcs iwmmxt
Known __fp16 formats (for use with the -mfp16-format= option):
alternative ieee none
Known ARM FPUs (for use with the -mfpu= option):
auto crypto-neon-fp-armv8 fp-armv8 fpv4-sp-d16 fpv5-d16 fpv5-sp-d16 neon neon-fp-armv8 neon-fp16 neon-vfpv3 neon-vfpv4 vfp vfp3 vfpv2 vfpv3
vfpv3-d16 vfpv3-d16-fp16 vfpv3-fp16 vfpv3xd vfpv3xd-fp16 vfpv4 vfpv4-d16
Valid arguments to -mtp=:
auto cp15 soft
Known floating-point ABIs (for use with the -mfloat-abi= option):
hard soft softfp
TLS dialect to use:
gnu gnu2
其实是支持浮点数的，只是设置架构和cpu时，没有指定精确，导致c库是vfpv3。阅读gcc11的手册。发现-march -mtune -mcpu -mfpu -mfloat-abi，精确设置如下：
150 CT_ARCH="arm"
151 CT_ARCH_CHOICE_KSYM="ARM"
152 CT_ARCH_CPU=""
153 CT_ARCH_TUNE=""
154 CT_ARCH_ARM_SHOW=y
202 CT_ARCH_ARCH="armv7-a+neon-vfpv4"
203 CT_ARCH_FPU="neon-vfpv4"
204 # CT_ARCH_FLOAT_AUTO is not set
205 CT_ARCH_FLOAT_HW=y
206 # CT_ARCH_FLOAT_SOFTFP is not set
207 # CT_ARCH_FLOAT_SW is not set
208 CT_TARGET_CFLAGS=""
209 CT_TARGET_LDFLAGS=""
210 CT_ARCH_FLOAT="hard"
参考：
1 https://github.com/rust-lang/rust/issues/58414
2 https://stackoverflow.com/questions/11727855/obtaining-current-gcc-architecture
Bug 23031 - [arm] SIGILL in memchr
4 https://sourceware.org/bugzilla/show_bug.cgi?id=23031
5 https://stackoverflow.com/questions/5115613/core-dump-file-analysis