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Re: GCC 10 issues
Re: GCC 10 issues
Fri, 21 Feb 2020 14:16:30 -0500
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
Greetings! I've committed a fix for these to the Version_2_6_13pre
branch. Thanks for your report! Please let me know if problems
Jerry James <address@hidden> writes:
> 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:
> 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
> COMPILER>>make: *** [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
> -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 "\\="?
Camm Maguire address@hidden
"The earth is but one country, and mankind its citizens." -- Baha'u'llah