[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 Michael Matz matz at gcc dot gnu.org changed: What|Removed |Added CC||matz at gcc dot gnu.org --- Comment #13 from Michael Matz matz at gcc dot gnu.org 2011-05-18 11:51:35 UTC --- The flag is for the compiler and tells it to no use (as in clobber) the red-zone.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #6 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-17 13:29:56 UTC --- (In reply to comment #5) Yeah, 128 bytes below %rsp can be freely used on x86_64, interrupts must not clobber those. I should have mentioned that this is kernel driver code, so then the interrupt does not change privilege level, and a stack switch will not occur. When an interrupt happens, the flags / cs / ip are stored at the next 24 bytes of stack, overwriting the variables in view here. I've seen this happen on a standard Suse 10 x86_64 Linux machine, so this would not be just theoretical...
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #7 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-17 13:42:23 UTC --- I think what is happening in the compiler BTW is that a sub $XX, %rsp is dropping out, perhaps as an optimization. If for example, you comment out the #define inline line in the test code, a stack adjustment appears: 0: 55 push %rbp 1: 48 89 e5mov%rsp,%rbp 4: 48 83 ec 10 sub$0x10,%rsp # SP adjustment here 8: 48 89 7d f8 mov%rdi,-0x8(%rbp) c: 89 75 f4mov%esi,-0xc(%rbp) etc. And as far as using stack space below your stack pointer, suppose someone has an operating system that runs applications at the same privilege level as the OS?
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #8 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-17 14:01:51 UTC --- It is of course fine if an interrupt uses the same stack, after all, user interrupts do that too. But the ABI says that 128 bytes below the %rsp are reserved, so the interrupt code first needs to subtract 128 from %rsp before calling any functions and must not modify that area. You can compile with -mno-red-zone to force no red zone. Apparently that's a flag x86_64-linux kernel uses during compilation and therefore probably doesn't bother to preserve the red zone during interrupts except when creating a user interrupt: arch/x86/Makefile has: KBUILD_CFLAGS += -mno-red-zone KBUILD_CFLAGS += -mcmodel=kernel Thus if you are compiling Linux kernel x86_64 code or modules without -mno-red-zone, it would be a user error.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #10 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-17 14:49:33 UTC --- And the compile (and the compile in the rc script here) is indeed specifying -mcmodel=kernel in the flags.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #9 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-17 14:47:34 UTC --- (In reply to comment #8) ... the ABI says that 128 bytes below the %rsp are reserved, so the interrupt code first needs to subtract 128 from %rsp before calling any functions and must not modify that area. Thanks for your reply, yet the interrupt itself will modify the next 24 bytes below %rsp, in storing flags / cs / rip. So then this area would be corrupted, which indeed I am seeing.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #11 from Mikael Pettersson mikpe at it dot uu.se 2011-05-17 16:58:02 UTC --- (In reply to comment #10) And the compile (and the compile in the rc script here) is indeed specifying -mcmodel=kernel in the flags. -mcmodel=kernel isn't enough, you're still failing to pass -mno-red-zone.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #12 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-17 18:42:47 UTC --- (In reply to comment #11) (In reply to comment #10) And the compile (and the compile in the rc script here) is indeed specifying -mcmodel=kernel in the flags. -mcmodel=kernel isn't enough, you're still failing to pass -mno-red-zone. That works, thanks! It does seem odd to tell it not to use the red zone, in order for it to um, properly use the red zone. :)
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #1 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-16 22:45:58 UTC --- Created attachment 24257 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=24257 The source file which generates the problem This file, when compiled via the attached rc script, will have references below the current stack pointer.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #2 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-16 22:49:14 UTC --- Created attachment 24258 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=24258 The output of running rc with -v -save-temps added. This is the output from running the rc script, with gcc parameters -v -save-temps added to the command line.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #4 from Andrew Pinski pinskia at gcc dot gnu.org 2011-05-16 23:09:13 UTC --- Well x86_64 ABI has a red zone which allows for these references to happen if they are under 128 bytes.
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 --- Comment #3 from Lee Merrill merrill_707_1 at yahoo dot com 2011-05-16 22:51:33 UTC --- A disassembly snippet to show the problem: fcPostWrite: 0: 55 push %rbp 1: 48 89 e5mov%rsp,%rbp # Note that these statements reference memory below the # current stack pointer. So any interrupt which occurs # here will corrupt these variables. 4: 48 89 7d e8 mov%rdi,-0x18(%rbp) 8: 89 75 e4mov%esi,-0x1c(%rbp) b: 8b 45 e4mov-0x1c(%rbp),%eax e: 89 45 fcmov%eax,-0x4(%rbp) 11: 48 8b 45 e8 mov-0x18(%rbp),%rax 15: 48 89 45 f0 mov%rax,-0x10(%rbp) 19: 48 8b 55 f0 mov-0x10(%rbp),%rdx 1d: 8b 45 fcmov-0x4(%rbp),%eax 20: 89 02 mov%eax,(%rdx) 22: c9 leaveq 23: c3 retq
[Bug c/49016] always_inline causes references below the current stack pointer
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49016 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED CC||jakub at gcc dot gnu.org Resolution||INVALID --- Comment #5 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-17 05:22:06 UTC --- Yeah, 128 bytes below %rsp can be freely used on x86_64, interrupts must not clobber those.
