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Can't compile "iwlwifi" module in Linux (lemmy.world)

submitted 1 year ago by nothingness@lemmy.world to c/programming@programming.dev

7 comments fedilink hide all child comments

I'm trying to build iwlwifi module manually and for my needs.

https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/iwlwifi-fixes.git/tree/net/wireless/

When I run Makefile as make, I get:

subcmd-util.h: In function ‘xrealloc’:
subcmd-util.h:58:31: error: pointer ‘ptr’ may be used after ‘realloc’ [-Werror=use-after-free]
   58 |                         ret = realloc(ptr, 1);
      |                               ^~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to ‘realloc’ here
   52 |         void *ret = realloc(ptr, size);
      |                     ^~~~~~~~~~~~~~~~~~
subcmd-util.h:56:23: error: pointer ‘ptr’ may be used after ‘realloc’ [-Werror=use-after-free]
   56 |                 ret = realloc(ptr, size);
      |                       ^~~~~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to ‘realloc’ here
   52 |         void *ret = realloc(ptr, size);
      |                     ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[4]: *** [/data/iwlwifi-fixes/tools/build/Makefile.build:97: /data/iwlwifi-fixes/tools/objtool/help.o] Error 1
make[3]: *** [Makefile:59: /data/iwlwifi-fixes/tools/objtool/libsubcmd-in.o] Error 2
make[2]: *** [Makefile:63: /data/iwlwifi-fixes/tools/objtool/libsubcmd.a] Error 2
make[1]: *** [Makefile:69: objtool] Error 2
make: *** [Makefile:1349: tools/objtool] Error 2

Why is it? How to fix it?

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[–] cbarrick@lemmy.world 2 points 1 year ago* (last edited 1 year ago) (2 children)

Why is it?

The code hitting that error is here:

https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/iwlwifi-fixes.git/tree/tools/lib/subcmd/subcmd-util.h

It looks fine to me.

What you are seeing is a warning that your compiler may have found a use-after-free bug, but I think this is a false positive. Your build is configured to turn this warning into a hard error.

How to fix it?

I think it will be difficult to know how to fix this without knowing more about your build setup. Are you passing any custom CFLAGS? What compiler and version are you using?

Also, here is someone asking about the same issue (in the same code) on Stack Exchange using GGC 12.1:

https://unix.stackexchange.com/questions/709671/linux-kernel-5-15-54-compilation-errors-with-gcc-12-1

This was the top result when Googling linux "-Werror=use-after-free".

I believe you can disable this warning in this file by adding a pragma after the includes (line 8):

#pragma GCC diagnostic ignored "-Wuse-after-free"

See https://stackoverflow.com/questions/925179/selectively-remove-a-warning-message-using-gcc

Edit: If you don't want to change the code, try disabling the use-after-free warning from the make call:

make CFLAGS="-Wno-use-after-free"

[–] nothingness@lemmy.world 0 points 1 year ago (1 children)

I think it will be difficult to know how to fix this without knowing more about your build setup. Are you passing any custom CFLAGS? What compiler and version are you using?

No.

gcc --version
gcc (GCC) 13.2.1 20230801

The goal - simply compile it for now.

[–] cbarrick@lemmy.world 1 points 1 year ago

If you don't want to change the code, try disabling the use-after-free warning from the make call:

make CFLAGS="-Wno-use-after-free"

[–] litchralee@sh.itjust.works 0 points 1 year ago* (last edited 1 year ago)

No objections to your answer to the OP's question, but as a curiosity, I'm trying to figure out what the original xrealloc() function is trying to do.

So far as I can tell, it tries a normal realloc() with the requested size, but if that fails, tries again with size=1. But strangely, it that fails, tries using the requested size a second time. And if that still fails, tries once more with size=1.

The POSIX man page isn't giving me any hints as to why size=1 might be special, or if this is some sort of Linux-specific behavior or workaround. I wondered if you might have some insight why this function is the way it is.

Note: I'm on mobile, so haven't checked the Git Blame history yet.