[COFF] Invalid symbol table entry in compiled Windows exectuable file, rejected by Golang PE/COFF parser #161030
Description
After upgrading Clang/LLVM from 20.1.8 to 21.1.1 in MSYS2 on Windows 11,
CGO stops working with the following error messages:
# runtime/cgo
cgo: cannot parse $WORK\b003\_cgo_.o as ELF, Mach-O, PE or XCOFF
offset 0 is before the start of string table
It turns out that invalid COFF file is produced by LLVM.
Some entries in symbol table have their 8 bytes of name field being all zero,
which corresponds to an invalid 0 offset to the string table.
The problem can be easily reproduced by a simple hello world program.
#include <stdio.h>
int main() {
printf("Hello World\n");
}clang -o hello.exe hello.c
The compiled executable runs successfully,
but objdump will expose the problem.
When objdump sees the invalid symbol names with offset 0,
it reads a string from the 4-byte header of the string table (which contains the size of the string table),
essentially reinterprets an integer into a string and outputs that string,
exposing the problem.
objdump.exe -t hello.exe
hello.exe: file format coff-x86-64
SYMBOL TABLE:
[ 0](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000000 .refptr._MINGW_INSTALL_DEBUG_MATHERR
...
[35](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x000015c0 _cexit
[36](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000878 ﾓ
...
[57](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x00001630 malloc
[58](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000908 ﾓ
[59](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x00001650 strlen
[60](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000918 ﾓ
[61](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x00001640 memcpy
[62](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000830 ﾓ
...
[67](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x00001620 exit
[68](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x000008c8 ﾓ
...
[145](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x000016e0 abort
[146](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x000008c0 ﾓ
...
[192](sec 1)(fl 0x00)(ty 20)(scl 2) (nx 0) 0x000017f0 strncmp
[193](sec 2)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000920 ﾓ
objdump.exe -d hello.exe
...
00000001400025c0 <_cexit>:
1400025c0: ff 25 b2 12 00 00 jmpq *0x12b2(%rip) # 0x140003878 <ﾓ
# >
...
0000000140002650 <strlen>:
140002650: ff 25 c2 12 00 00 jmpq *0x12c2(%rip) # 0x140003918 <ﾓ
# >
...
00000001400026e0 <abort>:
1400026e0: ff 25 da 11 00 00 jmpq *0x11da(%rip) # 0x1400038c0 <ﾓ
# >
...
00000001400027f0 <strncmp>:
1400027f0: ff 25 2a 11 00 00 jmpq *0x112a(%rip) # 0x140003920 <ﾓ
# >
...