Asking gcc to generate assembler code from your test code I can see that gcc do not call/malloc any builtin it generates inline code so there is nothing to free.
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.file "check-va.c"
.text
.type passdown, @function
passdown:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $48, %rsp
movq %rdi, -40(%rbp)
movq %rsi, -48(%rbp)
leaq -32(%rbp), %rax
movq -48(%rbp), %rdx
movq (%rdx), %rcx
movq %rcx, (%rax)
movq 8(%rdx), %rcx
movq %rcx, 8(%rax)
movq 16(%rdx), %rdx
movq %rdx, 16(%rax)
leaq -32(%rbp), %rdx
movq -40(%rbp), %rax
movq %rdx, %rsi
movq %rax, %rdi
call vprintf
movl %eax, -4(%rbp)
movl -4(%rbp), %eax
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.size passdown, .-passdown
.type myprintf, @function
myprintf:
.LFB1:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $224, %rsp
movq %rsi, -168(%rbp)
movq %rdx, -160(%rbp)
movq %rcx, -152(%rbp)
movq %r8, -144(%rbp)
movq %r9, -136(%rbp)
testb %al, %al
je .L3
movaps %xmm0, -128(%rbp)
movaps %xmm1, -112(%rbp)
movaps %xmm2, -96(%rbp)
movaps %xmm3, -80(%rbp)
movaps %xmm4, -64(%rbp)
movaps %xmm5, -48(%rbp)
movaps %xmm6, -32(%rbp)
movaps %xmm7, -16(%rbp)
.L3:
movq %rdi, -216(%rbp)
movl $8, -200(%rbp)
movl $48, -196(%rbp)
leaq 16(%rbp), %rax
movq %rax, -192(%rbp)
leaq -176(%rbp), %rax
movq %rax, -184(%rbp)
leaq -200(%rbp), %rdx
movq -216(%rbp), %rax
movq %rdx, %rsi
movq %rax, %rdi
call passdown
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE1:
.size myprintf, .-myprintf
.section .rodata
.LC1:
.string "bla"
.LC2:
.string "%s %i %f\n"
.text
.globl main
.type main, @function
main:
.LFB2:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movsd .LC0(%rip), %xmm0
movl $42, %edx
movl $.LC1, %esi
movl $.LC2, %edi
movl $1, %eax
call myprintf
movl $0, %eax
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE2:
.size main, .-main
.section .rodata
.align 8
.LC0:
.long 2576980378
.long 1071225241
.ident "GCC: (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3"
.section .note.GNU-stack,"",@progbits