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GCC 10 issues
From: |
Jerry James |
Subject: |
GCC 10 issues |
Date: |
Fri, 31 Jan 2020 14:02:29 -0700 |
Hi Camm,
The Fedora project is currently rebuilding all packages with what will
soon be GCC 10. I have encountered two issues so far and thought I
should give you a heads up.
GCC has long defaulted to -fcommon, but GCC 10 flips the default to
-fno-common. As a result, the link step fails with complaints about
lots of multiply-defined variables. A quick workaround is to add
-fcommon to the build flags. Otherwise, the code would have to be
altered to ensure that there is exactly one compilation unit
containing a definition for each variable.
After adding -fcommon, the build still fails like this:
COMPILER>
Error: ERROR "Caught fatal error [memory may be damaged]"
Signalled by EQUAL-TAIL-RECURSION-CHECK.
ERROR "Caught fatal error [memory may be damaged]"
Broken at SYSTEM::DO-BREAK-LEVEL. Type :H for Help.
1 Return to top level.
COMPILER>>2148155904 heap words available
NIL
COMPILER>>
NIL
COMPILER>>make[1]: *** [makefile:98: saved_pre_gcl] Error 255
Here is a disassembly of cclear_stack on an x86_64 machine:
0000000000005370 <cclear_stack>:
5370: f3 0f 1e fa endbr64
5374: 31 c0 xor %eax,%eax
5376: c3 retq
GCC 10 has concluded that it can optimize cclear_stack away, as that
simply returns 0. GCC may feel it is justified in doing so because of
this warning:
main.c: In function 'cclear_stack':
main.c:454:10: warning: function returns address of local variable
[
]8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wreturn-local-addr
-Wreturn-local-addr ]8;; ]
454 | return v;
| ^
In file included from /usr/include/stdlib.h:568,
from main.c:27:
main.c:452:11: note: declared here
452 | void *v=alloca(size);
| ^~~~~~
The same thing has happened with gcl_strncpy_chk; it just returns 0.
What are these functions supposed to do? EQUAL-TAIL-RECURSION-CHECK
in particular, even if cclear_stack is not optimized away, touches
memory it isn't allowed to touch, memory belonging to a stack frame
that has been popped. A conforming compiler is allowed to generate
code that segfaults (precisely what GCC 10 is doing).
I should also mention this output from the configure script:
checking finding default linker script... gawk: cmd. line:1: warning:
regexp escape sequence `\=' is not a known regexp operator
got it
Perhaps all of the "\=" should be "\\="?
Regards,
--
Jerry James
http://www.jamezone.org/
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