interrupt handler calls functions with misaligned stack

[hjl-tools]

Bugzilla Link	26477
Version	trunk
OS	Linux
CC	@hfinkel

Extended Description

Incoming stack of x86 interrupt handler is aligned at 4 bytes (8 bytes for
64-bit). When it calls extern functions, it needs to realign the stack
to 16-byte aligned if it is required:

[hjl@gnu-6 interrupt-1]$ cat xx.i 
extern void bar (void);

extern int i;

void
 __attribute__ ((interrupt))
foo (void *frame)
{
  bar ();
  i = 0;
}
[hjl@gnu-6 interrupt-1]$ /export/build/gnu/gcc-5/build-x86_64-linux/gcc/xgcc -B/export/build/gnu/gcc-5/build-x86_64-linux/gcc/ -O2 xx.i -m32 -mno-sse -S
[hjl@gnu-6 interrupt-1]$  cat xx.s
	.file	"xx.i"
	.section	.text.unlikely,"ax",@progbits
.LCOLDB0:
	.text
.LHOTB0:
	.p2align 4,,15
	.globl	foo
	.type	foo, @function
foo:
.LFB0:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	pushl	%ecx
	pushl	%edx
	pushl	%eax
	andl	$-16, %esp  <<<<<<<<<<<< Align stack
	cld
	.cfi_offset 1, -12
	.cfi_offset 2, -16
	.cfi_offset 0, -20
	call	bar
	movl	$0, i
	leal	-12(%ebp), %esp
	popl	%eax
	.cfi_restore 0
	popl	%edx
	.cfi_restore 2
	popl	%ecx
	.cfi_restore 1
	popl	%ebp
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	iret
	.cfi_endproc
.LFE0:
	.size	foo, .-foo
	.section	.text.unlikely
.LCOLDE0:
	.text
.LHOTE0:
	.ident	"GCC: (GNU) 5.3.1 20160201"
	.section	.note.GNU-stack,"",@progbits
[hjl@gnu-6 interrupt-1]$ 

But clang doesn't align stack:

[hjl@gnu-6 interrupt-1]$ /net/gnu-mic-2//export/build/gnu/llvm-clang/build-x86_64-linux/bin/clang -O2 xx.i -m32 -mno-sse -S
[hjl@gnu-6 interrupt-1]$  cat xx.s
	.text
	.file	"xx.i"
	.globl	foo
	.p2align	4, 0x90
	.type	foo,@function
foo:                                    # @foo
# BB#0:
	pushl	%esp
	pushl	%edx
	pushl	%ecx
	pushl	%eax
	subl	$12, %esp
	calll	bar
	movl	$0, i
	addl	$12, %esp
	popl	%eax
	popl	%ecx
	popl	%edx
	popl	%esp
	iretl
.Lfunc_end0:
	.size	foo, .Lfunc_end0-foo


	.ident	"clang version 3.9.0 (http://llvm.org/git/clang.git bf1d31e84aa2722174da56b8aff311ae04f4d9e1) (http://llvm.org/git/llvm.git 6cced9c3cd18f529420a03b100970d97512bb9a4)"
	.section	".note.GNU-stack","",@progbits
[hjl@gnu-6 interrupt-1]$

[antangelo]

I am interested in working on this for the 32-bit case. I believe the 64-bit case is already solved.

[RKSimon]

Candidate Patch: https://reviews.llvm.org/D151400

[llvmbot]

@llvm/issue-subscribers-backend-x86