On systems which use src/gmalloc.c but don't define HYBRID_MALLOC that file defines global replacements for malloc and other memory management functions. Strictly speaking, this results in undefined behaviour according to ISO C11 (wg14 n1570 draft) 7.1.3 and 7.22.3. But it used to work. However, with recent gcc versions and the default optimization level (-O2), most of the definition of calloc is replaced with a call to calloc (which the linker resolves to a call to that same calloc). Chances are temacs crashes because some library calls calloc. This happens with the gcc 5.2.0 release and also with the 6.0.0 20151108 snapshot. Please find below a self-contained test program which shows the problem (try gcc5 -Wall -g -O2 callocopt.c -o callocopt && ./callocopt 666, and then with -O instead of -O2, or even with -O2 -fno-optimize-strlen). For comparison purposes, I note that, meanwhile, the issue has also surfaced here http://permalink.gmane.org/gmane.os.freebsd.devel.cvs.src/210733 Back to the problem with gmalloc.c, I'd suggest the simple toolchain-independent work-around given in the patch below. A real fix is to use hybrid malloc.
callocopt.c
Description: Test program
0001-src-gmalloc.c-Always-define-gmalloc-and-friends.patch
Description: gcc 5 optimization work-around for gmalloc
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