Not related to this bug, can you mention your vi clone in ./USES which lists known projects using tcc.
C. -----Original Message----- From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=orange...@nongnu.org] On Behalf Of Kyryl Melekhin Sent: Tuesday, February 02, 2021 15:20 To: tinycc-devel@nongnu.org Subject: [Tinycc-devel] Jupm Optimizations regession bug Hello Grischka and Tcc community, I have found a regression bug in Tcc code gen (X86_64). Caused by this commit: 8227db3a23fd3cf11840eaa25eab5f3f5f813ac7 Sadly I don't have a small test case to reproduce it. But it is caused by stack allocation (unknown compile time alloca but in C99). You have to compile my text editor project, I get a crash in vfprintf in MuslC. The rsp pointer is corrupted. What is funny that crash is completely unrelated to the code that causes it, the reason I am 100% sure this is not a bug in any of my code is because first, I don't have any invalid accesses, tcc version compiled 1 commit behind from the commit above never crashes like that and also obviously it does not crash with any other compiler, gcc, clang, etc. Here is the 2 lines that cause invalid rsp instruction code gen. https://github.com/kyx0r/neatvi/blob/f6c46e9e8bdd8b1d4011d08019115936268e8536/vi.c#L1727 https://github.com/kyx0r/neatvi/blob/f6c46e9e8bdd8b1d4011d08019115936268e8536/vi.c#L1737 Why nobody had this dynamic array crashes before? As you can see the input for compiler is pretty complicated, there is a enclosed switch into if statements, and even more if statements everywhere. This is why I can't test the bug in more simple way, because it is unclear where the undefined behavior occurs in tcc. But from what I saw in that regression commit that if statements code gen was changed. Probably what happens now is the compiler places rsp restore instructions in the wrong places perhaps they are placed before the if statement inside switch. Also the code I linked does not have to run at all for it to crash, the only thing that has to happen is to be any of the cases of enclosing switch be true and execute. I can fix my code by simply not using the C99 stack allocated arrays in those spots, but that does not solve the obvious compiler bug. I will take a look into that commit more closely sometime later and maybe find a fix, but since grischka wrote it he may solve the bug before I do. Regards, Kyryl _______________________________________________ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel _______________________________________________ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
