What does "alloca" stand for?

Question

The alloca() function allocates memory in the stack frame of the caller. What did alloca originally stand for? Are there any sources regarding the etymology of the name?

Answer 1

I did some sleuthing in historic sources, and it seems that the "a" suffix in "alloca" stands for "automatic". "Automatic" is probably used in the sense of "automatically freed" or "automatic variable" (as in auto, the default C storage class for local variables; see discussion in the comments).

This commit message by Alejandro Colomar suggests that alloca appeared (separately?) in UNIX/32V and PWB/UNIX (both from the late 1970s). In the source archives linked, I found that each of those contains an alloca.s assembly file, each of which in turn refers to alloca as "automatic":

32v/usr/src/libc/sys/alloca.s

# like alloc, but automatic
# automatic free in return
.globl  _alloca
_alloca:
    .word   0x0000
    subl2   4(ap),sp    # crude allocation
    movl    16(fp),r1   # pc
    movq    8(fp),ap    # new (old) ap and fp
    bicl2   $3,sp       # 4-byte align
    addl2   $7*4,sp     # reuse space of mscp
    movl    sp,r0       # return value
    jmp     (r1)        # funny return

spencer_pwb/sys/source/s4/util/alloca.s

/   wdptr = alloca(nbytes);
/ like alloc, but automatic
/ automatic free upon return from calling function
.globl _alloca
_alloca:
    mov (sp)+,r1    / return
    mov (sp),r0     /count
    inc r0
    bic $1,r0       / round up
    sub r0,sp       / take core
    mov sp,r0
    tst (r0)+       / returned value; will generate
                / a memory fault if there isn't enough core
    jmp (r1)
.data
    <@(#)alloca 1.1\0>

P.S. When they say "like alloc", the alloc function they're referring to seems be a predecessor of the modern malloc, based on this function definition in PWB:

spencer_pwb/sys/source/s4/alloc.c

/*      alloc - old-style memory allocator
 *      returns -1 on fail rather than 0
*/
alloc(n)
{
        register p;
        p = malloc(n);
        return(p?p:-1);
}