multiple definition of in Nim generated static libraries

[JDragan]

Example

lib_a.nim

proc foo(): int32 {.exportc.} = return 24

lib_b.nim

proc bar(): int32 {.exportc.} = return 42

app.c

#include "stdio.h"
int main() {
  printf("%i\n", foo());
  printf("%i\n", bar());
}

nim c -d:release --mm:arc --app:staticlib --noMain --nimMainPrefix:libA --nimcache:ncache --out:libA.a lib_a.nim
nim c -d:release --mm:arc --app:staticlib --noMain --nimMainPrefix:libB --nimcache:ncache --out:libB.a lib_b.nim
gcc app.c libA.a libB.a -o app

Current Output

/usr/bin/ld: libB.a(@mlib_b.nim.c.o): in function `PreMainInner':
@mlib_b.nim.c:(.text+0x10): multiple definition of `PreMainInner'; libA.a(@mlib_a.nim.c.o):@mlib_a.nim.c:(.text+0x10): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o): in function `PreMain':
@mlib_b.nim.c:(.text+0x20): multiple definition of `PreMain'; libA.a(@mlib_a.nim.c.o):@mlib_a.nim.c:(.text+0x20): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o): in function `NimMainInner':
@mlib_b.nim.c:(.text+0x40): multiple definition of `NimMainInner'; libA.a(@mlib_a.nim.c.o):@mlib_a.nim.c:(.text+0x40): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o): in function `NimMainModule':
@mlib_b.nim.c:(.text+0x70): multiple definition of `NimMainModule'; libA.a(@mlib_a.nim.c.o):@mlib_a.nim.c:(.text+0x70): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o):(.bss+0x0): multiple definition of `gEnv'; libA.a(@mlib_a.nim.c.o):(.bss+0x0): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o):(.bss+0x8): multiple definition of `cmdLine'; libA.a(@mlib_a.nim.c.o):(.bss+0x8): first defined here
/usr/bin/ld: libB.a(@mlib_b.nim.c.o):(.bss+0x10): multiple definition of `cmdCount'; libA.a(@mlib_a.nim.c.o):(.bss+0x10): first defined here
collect2: error: ld returned 1 exit status

Expected Output

24
42

Possible Solution

• Emit NimMainModule_source_name_qwerty12345() instead of NimMainModule()
• Emit cmdCount_source_name_qwerty12345() instead of cmdCount()
• etc, etc...

Additional Information

Tested with --mm:arc --mm:orc --mm:refc --mm:none + with the --header option

$ nim -v
Nim Compiler Version 1.7.1 [Linux: amd64]
git hash: 19001c070bbe7645ff45fcbd66ab221235715302

[ghost]

You have to use the --nimMainPrefix switch 7ff43d0 so that each static library has it's own prefixes.

[JDragan]

The thing is that only NimMain() is renamed to libANimMain().
NimMainInner(), PreMain(), PreMainInner() are not prefixed with libA/libB, so their symbols clash...

[deech]

This issue is currently blocking progress for me, any way to get it prioritized?

[JDragan]

Maybe this will help, works on Windows. On Linux however, gEnv, cmdCount and cmdLine are still in the generated code, which shouldn't happen since the --noMain switch is used

diff --git a/compiler/cgen.nim b/compiler/cgen.nim
index ad59b759f..bb91b8624 100644
--- a/compiler/cgen.nim
+++ b/compiler/cgen.nim
@@ -1322,7 +1322,7 @@ proc getSomeInitName(m: BModule, suffix: string): Rope =
 proc getInitName(m: BModule): Rope =
   if sfMainModule in m.module.flags:
     # generate constant name for main module, for "easy" debugging.
-    result = rope"NimMainModule"
+    result = rope m.config.nimMainPrefix & "NimMainModule"
   else:
     result = getSomeInitName(m, "Init000")
 
@@ -1351,11 +1351,11 @@ proc genMainProc(m: BModule) =
     preMainCode.add("\tvoid* rtl_handle;\L")
     preMainCode.add(loadLib("rtl_handle", "nimGC_setStackBottom"))
     preMainCode.add(hcrGetProcLoadCode(m, "nimGC_setStackBottom", "nimrtl_", "rtl_handle", "nimGetProcAddr"))
-    preMainCode.add("\tinner = PreMain;\L")
+    preMainCode.add("\tinner = " & m.config.nimMainPrefix & "PreMain;\L")
     preMainCode.add("\tinitStackBottomWith_actual((void *)&inner);\L")
     preMainCode.add("\t(*inner)();\L")
   else:
-    preMainCode.add("\tPreMain();\L")
+    preMainCode.add("\t" & m.config.nimMainPrefix & "PreMain();\L")
 
   const
     # not a big deal if we always compile these 3 global vars... makes the HCR code easier
@@ -1370,20 +1370,20 @@ proc genMainProc(m: BModule) =
 
     PreMainVolatileBody =
       "\tvoid (*volatile inner)(void);$N" &
-      "\tinner = PreMainInner;$N" &
+      "\tinner = $3PreMainInner;$N" &
       "$1" &
       "\t(*inner)();$N"
 
     PreMainNonVolatileBody =
       "$1" &
-      "\tPreMainInner();$N"
+      "\t$3PreMainInner();$N"
 
     PreMainBodyStart = "$N" &
-      "N_LIB_PRIVATE void PreMainInner(void) {$N" &
+      "N_LIB_PRIVATE void $3PreMainInner(void) {$N" &
       "$2" &
       "}$N$N" &
       PosixCmdLine &
-      "N_LIB_PRIVATE void PreMain(void) {$N"
+      "N_LIB_PRIVATE void $3PreMain(void) {$N"
 
     PreMainBodyEnd =
       "}$N$N"
@@ -1394,21 +1394,21 @@ proc genMainProc(m: BModule) =
     MainProcsWithResult =
       MainProcs & ("\treturn $1nim_program_result;$N")
 
-    NimMainInner = "N_LIB_PRIVATE N_CDECL(void, NimMainInner)(void) {$N" &
+    NimMainInner = "N_LIB_PRIVATE N_CDECL(void, $5NimMainInner)(void) {$N" &
         "$1" &
       "}$N$N"
 
     NimMainVolatileBody =
       "\tvoid (*volatile inner)(void);$N" &
       "$4" &
-      "\tinner = NimMainInner;$N" &
+      "\tinner = $5NimMainInner;$N" &
       "$2" &
       "\t(*inner)();$N"
 
     NimMainNonVolatileBody =
       "$4" &
       "$2" &
-      "\tNimMainInner();$N"
+      "\t$5NimMainInner();$N"
 
     NimMainProcStart =
       "N_CDECL(void, $5NimMain)(void) {$N"
@@ -1488,9 +1488,9 @@ proc genMainProc(m: BModule) =
     else: ropecg(m, "\t#initStackBottomWith((void *)&inner);$N", [])
   inc(m.labels)
   if m.config.selectedGC notin {gcNone, gcArc, gcOrc}:
-    appcg(m, m.s[cfsProcs], PreMainBodyStart & PreMainVolatileBody & PreMainBodyEnd, [m.g.mainDatInit, m.g.otherModsInit])
+    appcg(m, m.s[cfsProcs], PreMainBodyStart & PreMainVolatileBody & PreMainBodyEnd, [m.g.mainDatInit, m.g.otherModsInit, m.config.nimMainPrefix])
   else:
-    appcg(m, m.s[cfsProcs], PreMainBodyStart & PreMainNonVolatileBody & PreMainBodyEnd, [m.g.mainDatInit, m.g.otherModsInit])
+    appcg(m, m.s[cfsProcs], PreMainBodyStart & PreMainNonVolatileBody & PreMainBodyEnd, [m.g.mainDatInit, m.g.otherModsInit, m.config.nimMainPrefix])
 
   if m.config.target.targetOS == osWindows and
       m.config.globalOptions * {optGenGuiApp, optGenDynLib} != {}:

[deech]

This is nice for now but we really need symbol isolation otherwise it's impossible to create C ABIs for Nim libraries because any two will clash on any common parts of their respective dependency tree including the standard library. It might be worth generalizing --nimMainPrefix=... to something like --nimPrefix=... that will do to all other visible symbols what nimMainPrefix does for NimMain, there is still potential for unpleasant overlap if two people pick the same prefix and the binary that uses them will be a little bloated with some redundant symbols but IMO it's worth it to be able to use Nim from other languages.

[deech]

This also seems promising, I had no idea you could use objcopy this way. https://stackoverflow.com/questions/6940384/how-to-deal-with-symbol-collisions-between-statically-linked-libraries/6940389#6940389

[JDragan]

imo --nimMainPrefix shouldn't exist.

When using --app:staticlib, --noMain should be activated and the prefix for these functions should be taken from the --out:SomeLib.a switch (instead NimMain(), one will call the initialization with SomeLibMain()) and this would be general rule no matter if you compile 1 or 1000 libraries.

[deech]

I discovered that if you can use the cpp backend the --cppCompileToNamespace:myLib flag will wrap all the generated C++ code in a namespace and prevent symbol clashes.

[Araq]

This works now.

[dmknght]

Hello! I'm having similar issue trying to build a static lib in Nim and then use an other Nim script to import the lib. (It's for testing only). I got similar issue and add --passL:-Wl,--allow-multiple-definition to Nim worked for me.

[waruqi]

Hello! I'm having similar issue trying to build a static lib in Nim and then use an other Nim script to import the lib. (It's for testing only). I got similar issue and add --passL:-Wl,--allow-multiple-definition to Nim worked for me.

It does not work now.

ld: unknown option: --allow-multiple-definition
clang: error: linker command failed with exit code 1 (use -v to see invocati
on)

xmake-io/xmake#4042 (comment)

[dmknght]

ld: unknown option: --allow-multiple-definition
clang: error: linker command failed with exit code 1 (use -v to see invocati
on)

This is NOT the error mentioned in the issue. The error log showed the compiler was clang.

[waruqi]

ld: unknown option: --allow-multiple-definition
clang: error: linker command failed with exit code 1 (use -v to see invocati
on)

This is NOT the error mentioned in the issue. The error log showed the compiler was clang.

I know, but earlier I used this method to solve this issue as well, but now it doesn't work.

Also, nim always calls clang as a linker on my machine. if this flag is not available, how should I resolve this issue. multiple definition of NimMainModule