Bug 23343 – ImportC: functions declared with asm label to set symbol name gets extra underscore prepended

Lots of libc functions on macOS are declared like: int open(const char *, int, ...) asm("_" "open" ); with the asm label to (pointlessly) set the symbol name. Apparently an extra underscore gets prepended at some point as the following C program will fail to link: --- // o.c int open(const char*, int, ...) asm("_" "open"); int main(){ int fd = open("/dev/null", 0); return fd >= 0 ? 0 : 1; } --- $ dmd o.c Undefined symbols for architecture x86_64: "__open", referenced from: _main in o.o ld: symbol(s) not found for architecture x86_64 Strangely though, if you write a D file to print the mangle of `open`: --- // op.d import o; pragma(msg, o.open.mangleof); // _open --- The extra underscore is not present. Output of `nm` also shows the extra underscore. $ nm -g o.o U __open 0000000000000000 T _main 0000000000000058 S _o.main.eh I don’t know if this issue affects other platforms.

This same issue also affects LDC.

The extra underscore is added by the backend/s, will take a look at fixing this

The _ prefix is added by obj_mangle2(): https://github.com/dlang/dmd/blob/master/compiler/src/dmd/backend/machobj.d#L2174

@WalterBright created dlang/dmd pull request #14485 "fix Issue 23343 - ImportC: functions declared with asm label to set s…" fixing this issue: - fix Issue 23343 - ImportC: functions declared with asm label to set symbol name gets extra underscore prepended https://github.com/dlang/dmd/pull/14485

@WalterBright created dlang/dmd pull request #14486 "fix Issue 23343 - ImportC: functions declared with asm label to set s…" fixing this issue: - fix Issue 23343 - ImportC: functions declared with asm label to set symbol name gets extra underscore prepended https://github.com/dlang/dmd/pull/14486