[cfe-dev] stack size issue

[Jonny Yu]

Hi Joerg,

Thanks for the reply.   I re-tried with -O0 so the my_assert function isn't inlined and the stack alloc is still 0x120.
 
Here's how I get the result.

clang -g -O0 -lstdc++  test_stack_alloc.cpp -o test_stack_alloc
otool -t -V test_stack_alloc | c++filt

recurse():
0000000100000cb0	pushq	%rbp
0000000100000cb1	movq	%rsp,%rbp
0000000100000cb4	subq	$0x00000120,%rsp
0000000100000cbb	movq	0x00000386(%rip),%rax
0000000100000cc2	movq	(%rax),%rax
0000000100000cc5	movq	%rax,0xf8(%rbp)
0000000100000cc9	callq	check_stack_limit()
0000000100000cce	leaq	0xfffffef0(%rbp),%rax
0000000100000cd5	movq	0x000003e4(%rip),%rcx
0000000100000cdc	subq	%rax,%rcx
0000000100000cdf	movq	%rcx,0xfffffee8(%rbp)
0000000100000ce6	cmpq	$0x0001e100,0xfffffee8(%rbp)
0000000100000cf1	jbe	0x100000cfc
0000000100000cf7	callq	my_assert()
0000000100000cfc	callq	recurse()
0000000100000d01	callq	recurse()
0000000100000d06	movq	0x0000033b(%rip),%rax
0000000100000d0d	movq	(%rax),%rax
0000000100000d10	movq	0xf8(%rbp),%rcx
0000000100000d14	cmpq	%rcx,%rax
0000000100000d17	jne	0x100000d26
0000000100000d1d	addq	$0x00000120,%rsp
0000000100000d24	popq	%rbp
0000000100000d25	ret
0000000100000d26	callq	0x100000d94	; symbol stub for: ___stack_chk_fail
0000000100000d2b	nopl	0x00(%rax,%rax)


Here's the LLVM GCC 4.2 .1 generates.

recurse():
0000000100000bc0	pushq	%rbp
0000000100000bc1	movq	%rsp,%rbp
0000000100000bc4	subq	$0x00000110,%rsp
0000000100000bcb	movq	0x0000047e(%rip),%rax
0000000100000bd2	movq	(%rax),%rax
0000000100000bd5	movq	%rax,0xf8(%rbp)
0000000100000bd9	callq	check_stack_limit()
0000000100000bde	movq	0x000004f3(%rip),%rax
0000000100000be5	leaq	0xfffffef8(%rbp),%rcx
0000000100000bec	subq	%rcx,%rax
0000000100000bef	movq	%rax,0xfffffef0(%rbp)
0000000100000bf6	movq	0xfffffef0(%rbp),%rax
0000000100000bfd	cmpq	$0x0001e100,%eax
0000000100000c03	jbe	0x100000c0a
0000000100000c05	callq	my_assert()
0000000100000c0a	callq	recurse()
0000000100000c0f	callq	recurse()
0000000100000c14	movq	0x00000435(%rip),%rax
0000000100000c1b	movq	(%rax),%rax
0000000100000c1e	movq	0xf8(%rbp),%rcx
0000000100000c22	cmpq	%rcx,%rax
0000000100000c25	jne	0x100000c30
0000000100000c27	addq	$0x00000110,%rsp
0000000100000c2e	popq	%rbp
0000000100000c2f	ret
0000000100000c30	callq	0x100000d46	; symbol stub for: ___stack_chk_fail
0000000100000c35	nopl	0x00(%rax,%rax)
0000000100000c3a	nopw	0x00(%rax,%rax)




On Mar 5, 2012, at 9:13 PM, Joerg Sonnenberger wrote:

> On Mon, Mar 05, 2012 at 06:40:47PM +0800, Yingshen Yu wrote:
>> Anyone can explain why clang needs alloc extra 16 bytes stack for the same
>> code?
> 
> my_assert is inlined and it uses the additional stack space for the
> arguments.
> 
> Joerg
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